Abstract

Optical fiber surface-enhanced Raman scattering (SERS) probes provide a novel platform for liquid-phase in situ and remote SERS detections. However, it is still a challenge to fabricate noble metal nanostructures with large SERS enhancement factor (EF) onto optical fiber surfaces. In this article, we successfully prepare Au-nanorod cluster structures on optical fiber facets by a laboratory-developed laser-induced evaporation self-assembly method. It is demonstrated that the optimized optical fiber SERS probes show high detection sensitivity (10−10 M for rhodamine 6G solution, and 10−8 M for malachite green or crystal violet solution) and excellent reproducibility (relative standard deviation less than 6%). As the laser-induced evaporation self-assembly method is a simple and low-cost method capable of achieving automatic and reproducible preparations of cluster patterned optical fiber SERS probes, this work may find important application prospects in various liquid-phase SERS detection areas.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. Introduction

Surface-enhanced Raman scattering (SERS) is a very sensitive molecule detection tool that has significant advantages such as simple pretreatment of the sample, short detection time, and fingerprint spectral characteristics [1,2]. Benefitting from the development of nanotechnology in recent decades, the performance of SERS detection has significantly improved, as evidenced by Raman enhancement factors (EFs) as high as 106-1012 being recently reported in the literature [3,4]. Owing to these advances, SERS technology has been widely applied in various areas such as food safety, chemistry, biology and environmental science. However, SERS is yet to become a general tool for practical detection applications, due to the difficulty in the fabrication of SERS substrates with macro-scale, uniform, and high-quality hotspots [5].

Recently, it has been shown that optical fiber SERS probes, which combine the SERS effect with the optical waveguide effect of optical fibers, are capable of realizing large SERS enhancement and good detection reproducibility, simultaneously [6,7]. Optical fiber SERS probes are usually formed by fabricating noble metal nanoparticles or nanostructures onto the surface of quartz optical fibers. During SERS detection, the Raman excitation laser is mode-propagated in the optical fiber for SERS excitation, and the SERS signals generated on the fiber surface are coupled back into the optical fiber, and collected in a backscattering arrangement [810]. On one hand, the guided-mode propagation characteristics of Raman excitation laser in optical fibers can effectively increase the light-matter interaction area, which may improve the generated SERS signal intensity, due to the significantly larger number of molecules stimulated. On the other hand, the SERS signals collected by the optical fiber probes are the integration over the whole SERS-active area, which greatly reduces the uniform distribution requirements of SERS hotspots, and improves the signal reproducibility [11,12]. In recent decades, optical fiber SERS probes have attracted considerable attention because of the potential advantages mentioned above, in addition to their liquid-phase in situ or remote SERS detection capability, which rendered them useful in such fields as environmental science [12], biosensing [13], and food safety [14]. Various nanofabrication techniques have been developed for the preparation of optical fiber SERS probes, including physical vapor deposition [15], chemical modification and immobilization [16], laser-induced reduction [17] and nanolithography [18]. However, due to the cylindrical surfaces and inert chemical property of quartz optical fibers, most of the SERS-active noble metal structures formed on optical fiber surfaces have the form of nanoparticle island films or scattered nanoparticles, which possess relatively low SERS EF that limits the SERS detection sensitivity of the optical fiber probes [9]. It remains a big challenge to fabricate noble metal nanostructures with large SERS EF on quartz optical fiber surfaces, which is crucial for improving the SERS sensitivity of these probes.

A nanoparticle cluster is one of the nanostructures that provide a very large SERS EF, due to the high local electric field enhancement that takes place in the small gaps between the particles [19,20]. Recently, a few methods have been proposed for the fabrication of nanoparticle clusters onto quartz optical fiber surfaces, to improve their SERS detection sensitivity. For example, Yap et al used template-guided self-assembly of gold nanoparticles to form a nanoparticle cluster array on the facet of an optical fiber, and realized a SERS EF of 107 [21]. However, the nanoparticles were randomly distributed on the template, duo to the lack of interparticle attraction, which limited the formation of high-quality hotspots. Recently, a method referred to as “decal transfer”, based on electron-beam lithography, may be used to fabricate nanoparticle cluster structures on optical fiber facets [18], but the method involved a complex fabrication process, and may not be suitable for probe preparation with high throughput.

In this article, we propose a novel laser-induced evaporation self-assembly method, to fabricate noble metal nanoparticle clusters on optical fiber facets. The method has significant advantages, such as low cost, simple operation, and the capability to realize automatic and reproducible high-throughput fabrication of cluster-patterned optical fiber SERS probes. Both the numerical simulations we performed using finite-difference time-domain (FDTD) method, and the experimental measurements, demonstrate that the nanocluster patterned fiber probes have excellent SERS detection sensitivity and good reproducibility, which may render them useful in important applications involving liquid-phase in situ detection.

2. Methods

2.1 Chemical and materials

Rhodamine 6G (R6G), malachite green (MG) and crystal violet (CV) were purchased from Sigma-Aldrich. Au nanorod colloid was purchased from NanoSeedz (Hong Kong). Multi-mode quartz optical fibers were purchased from Thorlabs. Milli-Q deionized water was used in all the experiments.

2.2 Preparation of optical fiber SERS probes

A laboratory-developed laser-induced evaporation self-assembly method was used to prepare the nanoparticle cluster patterned optical fiber SERS probes (Probe A). A 15-cm long multimode quartz optical fiber (200/220 µm, NA=0.22) was used for the preparation of the fiber SERS probes. One end of the fiber was connected with a 785-nm wavelength semiconductor laser, and the other end was cut by a fiber cleaver. In order to precisely control the position and movement of the fiber facet, the fiber was vertically fixed at the movable rod of a dip-coater that is controlled by a computer program to perform automatic pulling and dipping of the optical fiber. The probe fabrication process involved setting the laser source power to about 60 mW, then performing the dip-coating as follows: the fiber facet is first dipped into the colloid solution at a speed of 1000 µm/s and kept immersed for 3 s. Then, it is pulled out of the solution at a speed 250 µm/s, and kept suspended above the solution for 3 s. The total displacement was 0.5 mm. The initial position of the fiber facet was fixed at 0.15 - 0.2 mm above the solution surface.

Another kind of optical fiber SERS probes (Probe B) are fabricated by chemical modification and immobilization method, which has been the most widely used method for the fabrication of fiber SERS probes in the recent years [16,22]. Briefly, the sample was fabricated by first dipping the optical fiber facet in a 5% APTMS solution for 30 min for silane treatment, then immersing the treated fiber facet in Au nanorod colloid solution for 12 hours, and finally taking out the fiber facet and washing it with deionized water for several times.

2.3 Characterization and SERS measurements

Scanning electron microscopy (SEM) images of the fiber SERS probes were obtained with a high-resolution field-emission scanning electron microscope (SU8020, Hitachi, Japan). The SERS spectra were measured with a portable Raman spectrometer (QE-Pro, Ocean Optics, USA), using a laser excitation source with a wavelength of 785 nm. A laboratory-developed fiber Raman probe was used to couple the stimulating laser, the SERS probe, and the spectrometer. The modified end of the optical fiber SERS probe was completely soaked in the tested solution during the acquisition the SERS spectra. The power of the Raman excitation laser was set to 30 mW, and the spectral integration time was set to 2 s.

2.4 Simulation

Finite-difference time-domain (FDTD) method was used to calculate the near-field electric field distribution of the nanoparticle clusters, and perfectly matched layer (PML) boundary conditions were used in all the directions. The simulation size was set to 1 µm×1 µm ×1 µm, and the spatial grid size was 1 nm. The refractive index of gold was obtained from Palik [23]. The Au nanorods were 66 nm in length and 20 nm in diameter, according to the experimental data. The Au nanorods in the cluster were positioned and oriented according to the SEM images.

3. Results and discussion

3.1 General analysis of the evaporation self-assembly method

Evaporation induced self-assembly is a popular method used to fabricate noble metal nanostructures from their nanoparticle colloidal solutions [24,25]. When a droplet of nanoparticle colloid is dropped onto a planar substrate and left to dry naturally, a coffee-ring structure is most likely to form, due to the pinning effect of the contact line and the faster evaporation rate at the edge compared to that in the middle of the droplet [26,27]. Some methods, such as heating, can decrease the difference in the evaporation rate at different places of the droplet, leading to the formation of nanoparticles that are almost mono-dispersed in distribution [28,29]. In order to form the nanoparticle cluster structure, a hydrophilization or hydrophobization treatment of the substrate surface or the nanoparticle surface is usually required, where the slip effect of the droplet edge causes the aggregation of nanoparticles [30]. However, chemical modification of slippery omniphobic substrates is usually not easy to realize, and the intrinsic Raman signals of the modified molecules may influence the SERS detection of target molecules. Importantly, considering the small cross-section area of optical fibers, the above evaporation self-assembly methods is rarely used in the fabrication of optical fiber SERS probes.

The method we propose here, is a novel laser-induced evaporation self-assembly method to fabricate noble metal nanoparticle clusters directly on the fiber facet. Unlike the case with the droplet slip mechanism, the formation of clusters on the fiber facet by our method mainly originates from the inhomogeneous evaporation of a colloid droplet adhering to a fiber facet, as a result to the photothermal effect of noble metal nanoparticles, according to which noble metal nanoparticles in the colloid droplet absorb the laser energy and convert it to heat, thereby raising the local temperature and increasing the solvent evaporation rate near the nanoparticles. In addition, multiple laser-induced evaporation processes can be used to tune the nanoparticle number density on the optical fiber facet. We will show in this study that this laser-induced evaporation self-assembly method is simple, low in cost, and does not require any chemical modification pretreatment.

3.2 Self-assembly of Au nanorod clusters on fiber facet

The experimental setup of the laser-induced evaporation self-assembly method is shown in Fig. 1. In our experiment, a colloidal solution of Au nanorods (NR-20-780, optical density OD=10, Nanoseedz), with longitude plasmonic resonance wavelength of about 780 nm, is used as the nanoparticle colloid. Initially, the optical fiber flat facet is placed 0.15 mm above the colloidal solution surface. Then, it goes through multiple automatic dipping-pulling processes performed using the programmable dip-coater. During each slow pulling process, a colloid droplet adheres to the optical fiber facet due to surface tension [11], then undergoes a laser-induced evaporation in the air for several seconds, which results in the deposition of Au nanorods in the colloidal solution on the fiber facet.

 figure: Fig. 1.

Fig. 1. Experimental setup of the laser-induced evaporation self-assembly method.

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The process of self-assembly of Au nanorods on the optical fiber facet is studied. Figure 2 shows the SEM images of the optical fiber modified using 5, 10, 15 and 20 dipping-pulling cycles. Considering a flat-top electric field intensity distribution of 785-nm wavelength laser in the multimode optical fiber [31], the laser-induced self-assembly process of Au nanorods occurs in an almost identical manner at different places on the optical fiber facet, so, we choose to only show the SEM images within an area of 28×20 µm2 in the center of the optical fiber facet as representative of the entire sample surface. These SEM images show that many Au nanorod clusters appear on the optical fiber facet, and that increasing the number of dipping-pulling cycles increases the size of the Au nanorod cluster. Meanwhile, some new clusters are also formed, which leads to a visible increase in the cluster number density. Table 1 lists some relevant parameters obtained from Fig. 2. After 5 dipping-pulling cycles, a few Au nanorod clusters are seen sparsely distributed on the optical fiber facet [Fig. 2(a)], with a number density of only about 0.6 clusters/µm2, and the duty cycle of Au nanorods on the optical fiber facet of about 8%. The typical cluster in this case [inset in Fig. 2(a)] contains about 40 Au nanorods. When the number of dipping-pulling cycle is increased to 10, no obvious change in the cluster size was observed [Fig. 2(b)], while the typical cluster contained about 50 Au nanorods [inset in Fig. 2(b)]. However, the number density of the clusters, and the duty cycle of Au nanorods, both increase visibly. The number density of clusters for 10 dipping-pulling cycles is around 1.1 clusters/µm2, which is nearly twice as much as that of the 5 dipping-pulling cycles, and the duty cycle of Au nanorods is 13%. When the dipping-pulling cycle is further increased to 15, both the cluster number density and the cluster size increase again [Fig. 2(c)], as the typical nanocluster contains about 90 Au nanorods, the number density of clusters reaches 1.5 nanoclusters/µm2, and the duty cycle of Au nanorods increases to 23%. Meanwhile, we observe several much larger nanoclusters, which are formed by the merging of multiple neighboring clusters. As the dipping-pulling cycle number continues to increase, the number density of clusters begin to decrease, as more clusters are merging with each other, so the excessive heat from the photothermal effect of the large clusters may have caused the deformation of Au nanorods, as indicated by the spherical nanoparticles observed after 20 dipping-pulling cycles in Fig. 2(d).

 figure: Fig. 2.

Fig. 2. SEM image of fiber facets with different dip-coating cycles: (a) 5 cycles (b) 10 cycles (c) 15 cycles, and (d) 20 cycles. Some of the newly-formed clusters are marked with red circles.

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Tables Icon

Table 1. Evolution of the dipping-pulling process.

3.3 The mechanism and the optimization of formation of Au nanorod clusters on optical fiber facet

3.3.1 The mechanism

In order to better understand the formation process of Au nanorod clusters on the optical fiber facet, we analyzed the growth mechanism in detail. The main differences between our laser-induced evaporation self-assembly method and the conventional evaporation self-assembly methods lie in two aspects:

  • (1) Multiple evaporation processes: in a conventional evaporation self-assembly on a planar substrate, a colloid droplet (with the volume of about 50 µl) is dropped onto a substrate, and only one evaporation process is needed to self-assemble enough clusters for the fabrication of the SERS substrates. However, when evaporation self-assembly takes place on an optical fiber, the infinitely small volume of the colloid droplet adhering to the optical fiber facet (around one nanoliter), requires multiple evaporation processes to ensure suitable size and number density of the clusters.
  • (2) Laser-induced evaporation process: unlike typical naturally-occurring evaporation process, the colloid droplet adhering to the optical fiber, undergoes a laser-induced rapid evaporation process with every dipping-pulling cycle. Because the longitude plasmonic resonance peak of Au nanorod colloid (780 nm) is close to the center wavelength of the induced laser (785 nm), the Au nanorods in the colloid droplet adhering to the optical fiber facet will absorb the laser energy intensely, and convert it into heat, which increases the local temperature near the Au nanorods, and increases the local evaporation rate.
The growth process can be divided into two stages: a seeding stage, and a growing stage. The first several dipping-pulling cycles are the seeding stage [ Figs. 3(a)–3(c)], in which Au nanorods dispersed in the colloid droplets absorb the laser energy and cause the rise of the local temperature near the nanorods. Since the nanoparticles are uniformly distributed in the colloid droplets, and due to the Brownian motion of the nanoparticles, the colloid droplets are evenly heated and evaporated [Figs. 3(a) and 3(b)]. The initial temperature of the droplet approximately equals to that of nanoparticle colloid. As the solvent in the droplet eventually evaporates, the mass and heat capacity of the droplet gradually decreases, so, with the same heating power (as the amount of nanoparticles remains the same), the temperature of droplet rises rapidly, which increases the evaporation rate of solvent. When the solvent is completely evaporated, the Au nanorods within the droplet are deposited onto the fiber facet nearly monodispersely [Fig. 3(c)]. These monodispersed Au nanorods will act as seeds for the subsequent formation of clusters. In the following dipping-pulling cycles, called the growing stage, the deposited nanoparticles gradually accumulate, and the number of Au nanorods deposited on the optical fiber facet becomes much larger than that in the colloid droplet, leading these deposited nanorods to become the major heat source for the evaporation of the colloid droplet. When the optical fiber is just lifted out of the colloid surface, the colloid droplet adheres onto the optical fiber facet under the effect of surface tension. Subsequently, the evaporation of the colloid droplet in air undergoes two steps depending on the ratio of the droplet thickness Hdroplet to the radius of the local high temperature region near the seeds Rheat. In the beginning, Hdroplet >> Rheat [Fig. 3(d)]. The evaporation of droplet in this case will only happen on its surface, and the local high temperature near the seeds on the optical fiber facet will therefore have little effect on the surface evaporation, and mostly even evaporation of the droplet will take place. With further evaporation of the solvent, the droplet thickness becomes thinner. When the droplet thickness becomes comparable with (or less than) the radius of local high temperature region near the seeds on the optical fiber facet, i.e. HdropletRheat, the local high temperature near the seeds may greatly affect the evaporation rates at different locations on the droplet surface, e.g. the evaporation on the points above the cluster seeds occurs faster than it does elsewhere [Fig. 3(e)]. The nearby colloids will therefore flow into the region near the deposited nanoparticles to replenish the evaporation loss, dragging along new Au nanorods to the seeds on the optical fiber facet [Fig. 3(g)], and causing the formation of cluster structures [Fig. 3(f)]. The gradual accumulation of Au nanorods with the increase in the number of dipping-pulling cycles, causes the average size of Au nanorod clusters to become larger and larger [see Figs. 2(a)–2(c)], but on the other hand, small amounts of Au nanoparticles will deposit on empty areas to form new cluster seeds (red circles in Fig. 2). This can be seen from Fig. 2, as the density of clusters increases from 0.6 clusters/µm2 (corresponding to 5 dipping-pulling cycles) to 1.5 clusters/µm2 (corresponding to 15 dipping-pulling cycle). It should be pointed out that although more and more Au nanorods deposited onto the optical fiber facet, the total time taken to completely evaporate the droplet is basically the same (typically in 1.5-2.5 s) for each dipping-pulling cycle. The reasons are analyzed as follows. On one hand, there is a “cooling effect” during two adjacent dipping-pulling cycle, as the optical fiber facet is immersed back into the Au nanorod colloid and kept immersed for 3 s. On the other hand, more deposited nanoparticles on optical fiber may bring an obvious increase in the facet reflection of fiber, thus reduces the transmitted laser power for droplet heating. With further increase in the number of dipping-pulling cycles, as the number of nanorods contained in one cluster accumulates and finally exceeds a threshold, a deformation stage takes places because the photothermal effect of the deposited clusters will generate too much heat, which can result in the deformation of Au nanorods in the cluster, causing them to change their shapes into the sphere-like nanoparticles seen in Fig. 2(d).

 figure: Fig. 3.

Fig. 3. Schematic diagram of the nanocluster formation. (a)–(c) The seeding stage: as the solvent in the colloid droplet eventually evaporates, the Au nanorods within the droplet are deposited onto the fiber facet nearly monodispersely; (d)–(f) The growing stage: as the deposited nanoparticles gradually accumulate, when the droplet thickness becomes comparable with the radius of local high temperature region near the seeds on the optical fiber facet, the local high temperature near the seeds may greatly affect the evaporation rates at different locations on the droplet surface, e.g. the evaporation on the points above the cluster seeds occurs faster than it does elsewhere (g), and finally causing the formation of cluster structures.

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In addition, to intuitively reveal the important role of laser-induced evaporation process in the formation of cluster structure, we compare our probes with another kind of optical fiber SERS probes with same fabrication parameters except the heating process, where the fiber facet is heated to 60 °C by an oven every time when it is pulled out of the colloids, to make the droplet completely evaporated. Figure 4(a) shows the SEM image of optical fiber SERS probes fabricated under 15 dipping-pulling cycles without the laser. By comparing with the results shown in Fig. 2(c), much less Au nanorods are deposited on the optical fiber facet, and it is less likely to form Au nanorod cluster structure. Still, the SERS spectra of R6G aqueous solution are measured by the two probes, depicted in Fig. 4(b). The black line corresponds to the SERS spectrum of 10−8 M R6G solution measured by the probe fabricated with laser irradiation of 60 mW, and the red line corresponds to the SERS spectrum of 10−7 M R6G solution measured by the probe fabricated without laser irradiation (in an 60 °C oven). Despite the concentration of R6G of the former is one tenth of the latter, the SERS intensity of the former is nearly ten times higher than the latter. These results clearly demonstrate that the laser-induced localized evaporation process is critical for the formation of cluster patterned optical fiber SERS probes.

 figure: Fig. 4.

Fig. 4. (a) The SEM image of optical fiber SERS probes fabricated without laser irradiation. The dipping-pulling cycle is 15. (b) SERS spectra of R6G solution obtained by optical fiber SERS probes fabricated with (black line) and without (red line) laser irradiation.

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3.3.2 Optimized preparation of Au nanorod cluster patterned optical fiber probes

As the above results show, Au nanorod clusters can be successfully prepared on optical fiber facets by the laser-induced evaporation self-assembly method. We expect this kind of cluster patterned optical fiber probe to provide a very large SERS EF. In the following, we discuss the influence of various preparation conditions on the SERS performance of the probes.

The number of dipping-pulling cycles is critical for the formation of Au nanorod clusters on the optical fiber facet. Here, we fabricated nine optical fiber probes by the laser-induced evaporation self-assembly method, with the same experimental parameters except for the number of dipping-pulling cycles. Aqueous R6G solution with concentration of 10−8 M was used for SERS detection. During the SERS measurements, the prepared probes were directly dipped into the target solution, and the backscattering SERS signals collected by the optical fiber were detected using a portable Raman spectrometer with the integration time of 2 s. The SERS spectra measured using the nine optical fiber probes are shown in Fig. 5(a). All of these spectra were corrected by subtracting the Raman background of the optical fiber itself. From Fig. 5(a), distinct Raman peaks of R6G at 1127cm-1, 1185 cm-1, 1311 cm-1, 1362 cm-1, 1508 cm-1, 1600 cm-1, and 1649 cm-1 can be observed, and the SERS intensities vary for different dipping-pulling cycles. For comparison, we obtained the peak intensities at 1508 cm-1 for each dipping-pulling cycle, and presented them in Fig. 5(b). It can clearly be seen that the SERS intensity increases with the number of dipping-pulling cycles up to a certain value, and then decreases with further increase in the number of cycles. The figure also shows that the maximum SERS signal occurs at 15 dip-coating cycles. The increase of the SERS intensity from 5 to 15 dipping-pulling cycles is attributed to the gradual increase of Au nanorod cluster density and size, while the decrease of SERS intensity from 15 to 20 cycles is mainly caused by the deformation of Au nanorods into sphere-like nanoparticles. Additionally, we also noticed that the change starts to slow down as the intensity approaches its maximum value at 15 cycles. For example, when the number of dipping-pulling cycles changes from 5 to 10, the SERS intensity increases from 3100 to 6300, while near 15 ± 2 dipping-pulling cycles, the intensity shows only a comparatively small increase, from 7200 to 7800. Such minimal change in the SERS intensity as the number of dipping-pulling cycles nears an optimal value, is helpful to ensure good reproducibility in the preparation of cluster patterned fiber SERS probes.

 figure: Fig. 5.

Fig. 5. (a) The SERS spectra of R6G aqueous solution measured by optical fiber SERS probes fabricated with different dipping-pulling cycles; (b) The change in SERS intensity of the Raman peak at 1508 cm-1 with the number of dipping-pulling cycles.

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In addition to the number of dipping-pulling cycles, the power of the evaporation-inducing laser, the pulling speed of the dip-coater, and the residence time in air will also influence the fabrication of the cluster patterned fiber SERS probes. In our experiments, we kept the power of the laser fixed at 60 mW, the pulling speed at 250 µm/s, and the residence time at 3 s. Generally, the heat from the photothermal effect of the metal nanoparticles in the colloid droplet adhering to the fiber facet, is proportional to the laser power. If the laser power is too low, the temperature rise caused by the photothermal effect will not be sufficient to form nanoparticle clusters on the optical fiber facet. If the laser power is too high, on the other hand, the strong photothermal effect may cause boiling and breaking up of the colloid droplet on the optical fiber facet, and micro-coffee-ring patterns, instead of the nanoparticle clusters, will be formed due to the hot-plate effect [12]. In our current study, the laser power suitable for cluster formation was from 55 mW to 65 mW. The pulling speed of the dip-coater also influences the probes fabrication process. In a previous study, we observed that by slowly pulling up the optical fiber facet out of the nanoparticle colloid solution, a meniscus can be formed under the effect of liquid surface tension, and that the photothermal effect of nanoparticles at the meniscus causes a considerable increase in the nanoparticle concentration near the fiber facet [11], which is beneficial for the rapid formation of clusters on the optical fiber facet. Therefore, a pulling speed that is too high is not suitable for the formation of meniscus structure, while when the speed is too low, it may increase the total preparation time of the cluster structure. The experimental results in our current study showed that the optimal pulling speed was 150 - 250 µm/s. The residence time, described as the duration that the optical fiber facet is kept in the air, i.e. the laser-induced evaporation time in air, is another parameter that must be optimized to fabricate the probes with the right specifications, since an excessively long residence time may probably cause the damage of deposited nanoparticle clusters. By contrast, insufficient residence time can lead to incomplete evaporation of the colloid droplet, and result in the failure of the nanoparticles to form clusters. Our experimental results designated an optimal residence time of 3 s under the laser irradiation power of 60 mW.

3.4 SERS applications of Au nanorod clusters patterned optical fiber probes

In this section, we demonstrate the applicability of the probes fabricated by our new method. A series of Au-nanorod-clusters patterned optical fiber SERS probes were fabricated by the laser-induced evaporation self-assembly method, with the optimized experimental parameters as follows: the inducing-laser power was 60 mW, the number of dipping-pulling cycles was 15, the pulling speed was set to 200 µm/s, and the residence time in air set to 3 s. We should point out that it is simple to realize rapid, repeatable, and automatic preparation of optical fiber SERS probes with the help of a programmable dip-coater. Then, the reproducibility and sensitivity for SERS detections by the obtained probes were evaluated in detail. Finally, the high-performance probes were used for in situ SERS detection of MG and CV, which are toxic bactericide that are officially prohibited, but are still illegally being used as bactericides in aquaculture.

3.4.1 SERS detection reproducibility

Figure 6(a) displays the SERS spectra of 10−8 M R6G solution measured using ten different probes fabricated under the optimized experimental conditions. Good accordance between the results obtained using the ten probes can be observed. For comparison, the SERS intensities of three Raman peaks at 1182 cm-1, 1313 cm-1 and 1508 cm-1 were plotted in Fig. 6(b). The relative standard deviation (RSD) values for the three peak intensities were 4.5%, 3.8%, and 5.6%, respectively. The excellent SERS detection reproducibility originates from the following reasons. First, the SERS signals collected by optical fiber SERS probes are the integration of the whole SERS-active area, which effectively reduces the requirement of the uniformity throughout the cluster structures. Second, the laser-induced evaporation self-assembly method possesses good tolerance for the probe fabrication. As mentioned before, there is a tolerance range for the dipping-pulling cycles near the optimal value of 15, such that changing the dipping-pulling cycles near 15 ± 2, for example, had only a small influence on the SERS detection intensities. Third, the preparation of the optical fiber probes is controlled by a programmable dip-coater, which eliminates human errors and improves the repeatability of the fiber probes preparation process.

 figure: Fig. 6.

Fig. 6. The detection reproducibility of Au-nanorod-clusters patterned fiber SERS probes: (a) SERS spectra of 10−8 M R6G solution measured by ten fiber SERS probes (b) SERS intensities obtained from (a), for peaks at 1182 cm-1, 1313 cm-1, and 1508 cm-1.

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3.4.2 SERS detection sensitivity

To assess the detection sensitivity of the probes fabricated in our present work, the SERS spectra of R6G solutions with different concentrations from 10−7 M to 10−10 M were measured. Four probes were fabricated by the laser-induced evaporation self-assembly method under optimized conditions, then were individually dipped into R6G solutions with different concentrations for SERS detections. The measured results are given in Fig. 7(a), and show that the SERS intensity gradually decreased with the decrease in the sample concentration. The results also show that visible SERS peaks characteristic of R6G can be observed at a concentration as low as 10−10 M. Therefore, a limit of detection (LOD) lower than 10−10 M for R6G can be achieved with the probes fabricated using our new method. It should be noticed that our experiments used direct liquid-phase in situ detection, and that all the SERS spectra were acquired using only a portable Raman spectrometer and with an integration time as short as 2 s. Nevertheless, the detection sensitivity was comparable to or even better than other recently reported dry-state SERS detection results, which detected R6G using confocal Raman spectrometers with longer spectral integration time [32,33].

 figure: Fig. 7.

Fig. 7. (a) SERS spectra of R6G solutions with concentration of 10−7 M to 10−10 M, obtained with Au-nanorod-clusters patterned fiber SERS probes; (b) Comparison between the cluster patterned fiber SERS probes and typical fiber SERS probes fabricated using the chemical modification and immobilization method.

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Next, in order to obtain an intuitive understanding of the detection sensitivity, we compare the SERS detection results of R6G solution measured by the Au nanorod clusters patterned optical fiber SERS probes (hereinafter called probe A), versus optical fiber SERS probes fabricated with the widely used chemical modification and immobilization method (CMIM) (probes B) [34]. Figure 7(b) shows the comparison results. We can see that despite the concentration being 100 times lower, the peak intensity for probe A is still about 5 times higher than that for probe B. This highly superior detection sensitivity for probe A mainly originates from the higher SERS EF for the cluster structure. Figures 8(a) and 8(b) displays the calculated electric-field intensity distribution using FDTD method, for a cluster containing 82 Au nanorods and 82 mono-dispersed Au nanorods, respectively. The orientation of the Au nanorods is arranged according to the cluster shown in the inset of Fig. 2(c). According to our simulation results, the maximal local electric field enhancement factor ($|{E/{E_0}} |$) in the narrow gaps of the cluster structure is as large as 193, while for a single Au nanorod, the maximal electric field EF is 61. Here, for comparison, the color scales of Figs. 8(a) and 8(b) are identical, and the electric field ($|{E/{E_0}} |$) larger than 40 is represented as red. It is well known that SERS EF is approximately proportional to the fourth power of the local electric field enhancement factor [35]. Here, we calculate the average of ${|{E/{E_0}} |^4}$ in the whole area shown in Figs. 8(a) and 8(b), including the empty area with no nanoparticles. Theoretically, this should be proportional to the total Raman signal intensity. The calculated mean value of ${|{E/{E_0}} |^4}$ for Au nanorod cluster and mono-dispersed Au nanorods were 5.3×104 and 1.2×102, respectively. The ratio of the former to the latter is about 420, which is in good agreement with the experimental results.

 figure: Fig. 8.

Fig. 8. Theoretical electric-field intensity distribution, calculated for (a) an Au nanorod cluster, and (b) isolated Au nanorods, respectively. The total numbers of Au nanorods are the same for both cases. For comparison, the color bar is identical for both (a) and (b).

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3.4.3 Applications

From above analyses, we conclude that the Au-nanorod-clusters patterned optical fiber SERS probes can simultaneously achieve high sensitivity and excellent reproducibility in SERS detection applications, and are especially suitable for liquid-phase in situ SERS detections, benefitting from the optical propagation characteristics of the optical fiber. As a demonstration of a practical application, we tried to use this kind of optical fiber probes to realize highly sensitive, rapid and in situ SERS detection of two illegal bactericides widely used in aquaculture. MG and CV, as two kinds of triphenyl methane dyes, were commonly used as water bactericides in aquaculture for disease prevention and treatment, due to their broad-spectrum bactericidal effect, low cost, and easy access [36]. However, recent studies have proved that MG and CV have high toxicity, high residue and carcinogenic risk, and the two chemicals have been forbidden from use in aquaculture therapeutic applications [37,38]. Here, we obtained some water from a local fishpond, which did not contain MG or CV. After multiple centrifugations, the aquaculture water was used as the solvent to prepare MG or CV solutions with different concentrations. Considering that most portable Raman spectrometers are equipped with minicentrifuges, this centrifugation operation does not add extra difficulty for field detection. By dipping the as-prepared Au nanorod cluster patterned optical fiber SERS probes into the MG or CV solutions, the direct liquid-phase in situ SERS spectra were recorded and shown in Fig. 9. The background signal from the aquaculture water itself were removed for all the spectra, and the main Raman peaks for CV and MG were both observed. It is notable that in the practical SERS detections in field, if a “pure” aquaculture water (not contain the target molecules) is not easy to be acquired, the deionized water in laboratory can be used to obtain the background removement for the spectra, although it may bring some noise. Even though the SERS detection was performed using a portable Raman spectrometer, and with a short integration time of only 2 s, the sensitivity of the liquid-phase in situ SERS detection was better than 10−8 M for both CV and MG, which shows that the probes fabricated in our new method may find important application in the field of rapid inspection of illegal additives in the aquaculture or food industry.

 figure: Fig. 9.

Fig. 9. SERS spectra obtained by Au-nanorod-clusters patterned optical fiber SERS probes for (a) CV and (b) MG solutions.

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4. Conclusions

In this work, Au nanorod clusters were successfully fabricated on optical fiber facets by a simple and low-cost laser-induced evaporation self-assembly method. The formation mechanism of the Au nanorod clusters on optical fiber facet was analyzed in detail, revealing that under the irradiation of the laser propagating in an optical fiber, the photothermal effect of noble metal nanoparticles may cause obvious increase in the local temperature near the nanoparticles, which causes the evaporation of a colloid droplet adhering to the optical fiber facet to change from uniform to non-uniform evaporation. The non-uniform evaporation in the droplet causes the nanoparticles in the colloid to migrate towards previously deposited nanoparticles, and form nanoparticle clusters. With multiple dipping-pulling cycles, the clusters become larger and larger, and some new clusters appear on the optical fiber facet, which gradually increases the cluster density.

Using optimized fabrication parameters, the as prepared Au-nanorod-clusters patterned optical fiber probes demonstrated high SERS detection sensitivity, and excellent detection reproducibility. The probes were successfully used for liquid-phase in situ detection of 10−10 M of R6G, and the RSD of SERS intensity was less than 6%. To demonstrate the practical applicability of this kind of probes, they were used to detect the presence of two illegal bactericides, MG and CV, in aquaculture water, achieving rapid (spectral integration time of 2 s) and highly sensitive (10−8 M for both MG and CV) in situ SERS detection. The use of a programmable dip-coater allowed the automatic preparation of batches of optical fiber SERS probes that performed with high sensitivity and excellent reproducibility. The probes fabricated using our new method may find important applications in liquid-phase in situ detection fields such as food safety, environmental science, and biosensing.

Funding

National Natural Science Foundation of China (11874111, 51771189, 61771138); Science and Technology Planning Project of Guangdong Province (2017A010102019); Dongguan Social Science and Technology Development Project (2019507140172).

Disclosures

The authors declare no conflicts of interest.

References

1. B. Sharma, R. R. Frontiera, A. I. Henry, E. Ringe, and R. P. Van Duyne, “SERS: Materials, applications, and the future,” Mater. Today 15(1-2), 16–25 (2012). [CrossRef]  

2. N. M. B. Perney, J. J. Baumberg, M. E. Zoorob, M. D. B. Charlton, S. Mahnkopf, and C. M. Netti, “Tuning localized plasmons in nanostructured substrates for surface- enhanced Raman scattering,” Opt. Express 14(2), 847–857 (2006). [CrossRef]  

3. G. K. Pandey, N. K. Pathak, A. Ji, H. Pathak, and R. P. Sharma, “Study of Surface Enhanced Raman Scattering of Single Molecule Adsorbed on the Surface of Metal Nanogeometries: Electrostatic Approach,” Plasmonics 11(5), 1343–1349 (2016). [CrossRef]  

4. J. Song, J. H. Xian, M. H. Yu, D. Wang, S. Ye, H. B. Niu, X. Peng, and J. L. Qu, “Ultrahigh Enhancement Factor by Using a Silver Nanoshell With a Gain Core Above a Silver Substrate for Surface-Enhanced Raman Scattering at the Single-Molecule Level,” IEEE Photonics J. 7(5), 1–8 (2015). [CrossRef]  

5. R. Panneerselvam, G. K. Liu, Y. H. Wang, J. Y. Liu, S. Y. Ding, J. F. Li, D. Y. Wu, and Z. Q. Tian, “Surface-enhanced Raman spectroscopy: bottlenecks and future directions,” Chem. Commun. 54(1), 10–25 (2018). [CrossRef]  

6. Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015). [CrossRef]  

7. T. Hutter, S. R. Elliott, and S. Mahajan, “Optical fibre-tip probes for SERS: numerical study for design considerations,” Opt. Express 26(12), 15539–15550 (2018). [CrossRef]  

8. Y. Zhu, R. A. Dluhy, and Y. P. Zhao, “Development of silver nanorod array based fiber optic probes for SERS detection,” Sens. Actuators, B 157(1), 42–50 (2011). [CrossRef]  

9. C. Wang, L. H. Zeng, Z. Li, and D. L. Li, “Review of optical fibre probes for enhanced Raman sensing,” J. Raman Spectrosc. 48(8), 1040–1055 (2017). [CrossRef]  

10. M. Pisco, F. Galeotti, G. Quero, A. Iadicicco, M. Giordano, and A. Cusano, “Miniaturized Sensing Probes Based on Metallic Dielectric Crystals Self-Assembled on Optical Fiber Tips,” ACS Photonics 1(10), 917–927 (2014). [CrossRef]  

11. Y. Liu, Z. L. Huang, F. Zhou, X. Lei, B. Yao, G. W. Meng, and Q. H. Mao, “Highly sensitive fibre surface-enhanced Raman scattering probes fabricated using laser-induced self-assembly in a meniscus,” Nanoscale 8(20), 10607–10614 (2016). [CrossRef]  

12. Y. Liu, F. Zhou, H. Wang, X. Huang, and D. Ling, “Micro-coffee-ring-patterned fiber SERS probes and their in situ detection application in complex liquid environments,” Sens. Actuators, B 299, 126990 (2019). [CrossRef]  

13. Y. Liu, J. Y. Guang, C. Liu, S. Bi, Q. Liu, P. Li, N. Zhang, S. M. Chen, H. Z. Yuan, D. P. Zhou, and W. Peng, “Simple and Low-Cost Plasmonic Fiber-Optic Probe as SERS and Biosensing Platform,” Adv. Opt. Mater. 7(19), 1900337 (2019). [CrossRef]  

14. V. Tran, B. Walkenfort, M. Konig, M. Salehi, and S. Schlucker, “Rapid, Quantitative, and Ultrasensitive Point-of-Care Testing: A Portable SERS Reader for Lateral Flow Assays in Clinical Chemistry,” Angew. Chem. Int. Ed. 58(2), 442–446 (2019). [CrossRef]  

15. C. G. Danny, A. Subrahmanyam, and V. V. R. Sai, “Development of plasmonic U-bent plastic optical fiber probes for surface enhanced Raman scattering based biosensing,” J. Raman Spectrosc. 49(10), 1607–1616 (2018). [CrossRef]  

16. Z. L. Huang, X. Lei, Y. Liu, Z. W. Wang, X. J. Wang, Z. M. Wang, Q. H. Mao, and G. W. Meng, “Tapered Optical Fiber Probe Assembled with Plasmonic Nanostructures for Surface-Enhanced Raman Scattering Application,” ACS Appl. Mater. Interfaces 7(31), 17247–17254 (2015). [CrossRef]  

17. Z. Yin, Y. F. Geng, Q. L. Xie, X. M. Hong, X. L. Tan, Y. Z. Chen, L. L. Wang, W. J. Wang, and X. J. Li, “Photoreduced silver nanoparticles grown on femtosecond laser ablated, D-shaped fiber probe for surface-enhanced Raman scattering,” Appl. Opt. 55(20), 5408–5412 (2016). [CrossRef]  

18. E. J. Smythe, M. D. Dickey, J. M. Bao, G. M. Whitesides, and F. Capasso, “Optical Antenna Arrays on a Fiber Facet for in Situ Surface-Enhanced Raman Scattering Detection,” Nano Lett. 9(3), 1132–1138 (2009). [CrossRef]  

19. A. Ali, E. Y. Hwang, J. Choo, and D. W. Lim, “PEGylated nanographene-mediated metallic nanoparticle clusters for surface enhanced Raman scattering-based biosensing,” Analyst 143(11), 2604–2615 (2018). [CrossRef]  

20. A. Khaleque, E. G. Mironov, J. H. Osorio, Z. Y. Li, C. M. B. Cordeiro, L. M. Liu, M. A. R. Franco, J. L. Liow, and H. T. Hattori, “Integration of bow-tie plasmonic nano-antennas on tapered fibers,” Opt. Express 25(8), 8986–8996 (2017). [CrossRef]  

21. F. L. Yap, P. Thoniyot, S. Krishnan, and S. Krishnamoorthy, “Nanoparticle Cluster Arrays for High-Performance SERS through Directed Self-Assembly on Flat Substrates and on Optical Fibers,” ACS Nano 6(3), 2056–2070 (2012). [CrossRef]  

22. P. Vaiano, B. Carotenuto, M. Pisco, A. Ricciardi, G. Quero, M. Consales, A. Crescitelli, E. Esposito, and A. Cusano, “Lab on Fiber Technology for biological sensing applications,” Laser Photonics Rev. 10(6), 922–961 (2016). [CrossRef]  

23. E. D. Palik, Handbook of Optical Constants of Solids (Academic, 1997).

24. P. H. Qiu, C. Jensen, N. Charity, R. Towner, and C. B. Mao, “Oil Phase Evaporation-Induced Self-Assembly of Hydrophobic Nanoparticles into Spherical Clusters with Controlled Surface Chemistry in an Oil-in-Water Dispersion and Comparison of Behaviors of Individual and Clustered Iron Oxide Nanoparticles,” J. Am. Chem. Soc. 132(50), 17724–17732 (2010). [CrossRef]  

25. J. Xu, J. F. Xia, and Z. Q. Lin, “Evaporation-induced self-assembly of nanoparticles from a sphere-on-flat geometry,” Angew. Chem. Int. Ed. 46(11), 1860–1863 (2007). [CrossRef]  

26. R. D. Deegan, O. Bakajin, T. F. Dupont, G. Huber, S. R. Nagel, and T. A. Witten, “Capillary flow as the cause of ring stains from dried liquid drops,” Nature 389(6653), 827–829 (1997). [CrossRef]  

27. X. Y. Shen, C. M. Ho, and T. S. Wong, “Minimal Size of Coffee Ring Structure,” J. Phys. Chem. B 114(16), 5269–5274 (2010). [CrossRef]  

28. P. J. Yunker, T. Still, M. A. Lohr, and A. G. Yodh, “Suppression of the coffee-ring effect by shape-dependent capillary interactions,” Nature 476(7360), 308–311 (2011). [CrossRef]  

29. H. Hu and R. G. Larson, “Marangoni Effect Reverses Coffee-Ring Depositions,” J. Phys. Chem. B 110(14), 7090–7094 (2006). [CrossRef]  

30. S. K. Yang, X. M. Dai, B. B. Stogin, and T. S. Wong, “Ultrasensitive surface-enhanced Raman scattering detection in common fluids,” Proc. Natl. Acad. Sci. U. S. A. 113(2), 268–273 (2016). [CrossRef]  

31. K. Okamoto, Fundamentals of Optical Waveguides 2nd Edition (Academic, 2005).

32. Q. Zhang, Y. F. Yuan, C. P. Wang, Z. J. Zhou, L. Li, S. J. Zhang, and J. H. Xu, “Design considerations for SERS detection in colloidal solution: reduce spectral intensity fluctuation,” J. Raman Spectrosc. 47(4), 395–401 (2016). [CrossRef]  

33. K. B. Zhang, T. X. Zeng, X. L. Tan, W. D. Wu, Y. J. Tang, and H. B. Zhang, “A facile surface-enhanced Raman scattering (SERS) detection of rhodamine 6G and crystal violet using Au nanoparticle substrates,” Appl. Surf. Sci. 347, 569–573 (2015). [CrossRef]  

34. Y. Ran, P. Strobbia, V. Cupil-Garcia, and T. Vo-Dinh, “Fiber-optrode SERS probes using plasmonic silver-coated gold nanostars,” Sens. Actuators, B 287, 95–101 (2019). [CrossRef]  

35. P. L. Stiles, J. A. Dieringer, N. C. Shah, and R. R. Van Duyne, “Surface-Enhanced Raman Spectroscopy,” Annu. Rev. Anal. Chem. 1(1), 601–626 (2008). [CrossRef]  

36. D. J. Alderman, “Malachite green: a review,” J. Fish Dis. 8(3), 289–298 (1985). [CrossRef]  

37. J. C. Hashimoto, J. A. R. Paschoal, J. F. de Queiroz, and F. G. R. Reyes, “Considerations on the Use of Malachite Green in Aquaculture and Analytical Aspects of Determining the Residues in Fish: A Review,” J. Aquat. Food Prod. Technol. 20(3), 273–294 (2011). [CrossRef]  

38. J. B. Lee, H. Y. Kim, Y. M. Jang, J. Y. Song, S. M. Woo, M. S. Park, H. S. Lee, S. K. Lee, and M. Kim, “Determination of malachite green and crystal violet in processed fish products,” Food Addit. Contam., Part A 27(7), 953–961 (2010). [CrossRef]  

References

  • View by:

  1. B. Sharma, R. R. Frontiera, A. I. Henry, E. Ringe, and R. P. Van Duyne, “SERS: Materials, applications, and the future,” Mater. Today 15(1-2), 16–25 (2012).
    [Crossref]
  2. N. M. B. Perney, J. J. Baumberg, M. E. Zoorob, M. D. B. Charlton, S. Mahnkopf, and C. M. Netti, “Tuning localized plasmons in nanostructured substrates for surface- enhanced Raman scattering,” Opt. Express 14(2), 847–857 (2006).
    [Crossref]
  3. G. K. Pandey, N. K. Pathak, A. Ji, H. Pathak, and R. P. Sharma, “Study of Surface Enhanced Raman Scattering of Single Molecule Adsorbed on the Surface of Metal Nanogeometries: Electrostatic Approach,” Plasmonics 11(5), 1343–1349 (2016).
    [Crossref]
  4. J. Song, J. H. Xian, M. H. Yu, D. Wang, S. Ye, H. B. Niu, X. Peng, and J. L. Qu, “Ultrahigh Enhancement Factor by Using a Silver Nanoshell With a Gain Core Above a Silver Substrate for Surface-Enhanced Raman Scattering at the Single-Molecule Level,” IEEE Photonics J. 7(5), 1–8 (2015).
    [Crossref]
  5. R. Panneerselvam, G. K. Liu, Y. H. Wang, J. Y. Liu, S. Y. Ding, J. F. Li, D. Y. Wu, and Z. Q. Tian, “Surface-enhanced Raman spectroscopy: bottlenecks and future directions,” Chem. Commun. 54(1), 10–25 (2018).
    [Crossref]
  6. Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
    [Crossref]
  7. T. Hutter, S. R. Elliott, and S. Mahajan, “Optical fibre-tip probes for SERS: numerical study for design considerations,” Opt. Express 26(12), 15539–15550 (2018).
    [Crossref]
  8. Y. Zhu, R. A. Dluhy, and Y. P. Zhao, “Development of silver nanorod array based fiber optic probes for SERS detection,” Sens. Actuators, B 157(1), 42–50 (2011).
    [Crossref]
  9. C. Wang, L. H. Zeng, Z. Li, and D. L. Li, “Review of optical fibre probes for enhanced Raman sensing,” J. Raman Spectrosc. 48(8), 1040–1055 (2017).
    [Crossref]
  10. M. Pisco, F. Galeotti, G. Quero, A. Iadicicco, M. Giordano, and A. Cusano, “Miniaturized Sensing Probes Based on Metallic Dielectric Crystals Self-Assembled on Optical Fiber Tips,” ACS Photonics 1(10), 917–927 (2014).
    [Crossref]
  11. Y. Liu, Z. L. Huang, F. Zhou, X. Lei, B. Yao, G. W. Meng, and Q. H. Mao, “Highly sensitive fibre surface-enhanced Raman scattering probes fabricated using laser-induced self-assembly in a meniscus,” Nanoscale 8(20), 10607–10614 (2016).
    [Crossref]
  12. Y. Liu, F. Zhou, H. Wang, X. Huang, and D. Ling, “Micro-coffee-ring-patterned fiber SERS probes and their in situ detection application in complex liquid environments,” Sens. Actuators, B 299, 126990 (2019).
    [Crossref]
  13. Y. Liu, J. Y. Guang, C. Liu, S. Bi, Q. Liu, P. Li, N. Zhang, S. M. Chen, H. Z. Yuan, D. P. Zhou, and W. Peng, “Simple and Low-Cost Plasmonic Fiber-Optic Probe as SERS and Biosensing Platform,” Adv. Opt. Mater. 7(19), 1900337 (2019).
    [Crossref]
  14. V. Tran, B. Walkenfort, M. Konig, M. Salehi, and S. Schlucker, “Rapid, Quantitative, and Ultrasensitive Point-of-Care Testing: A Portable SERS Reader for Lateral Flow Assays in Clinical Chemistry,” Angew. Chem. Int. Ed. 58(2), 442–446 (2019).
    [Crossref]
  15. C. G. Danny, A. Subrahmanyam, and V. V. R. Sai, “Development of plasmonic U-bent plastic optical fiber probes for surface enhanced Raman scattering based biosensing,” J. Raman Spectrosc. 49(10), 1607–1616 (2018).
    [Crossref]
  16. Z. L. Huang, X. Lei, Y. Liu, Z. W. Wang, X. J. Wang, Z. M. Wang, Q. H. Mao, and G. W. Meng, “Tapered Optical Fiber Probe Assembled with Plasmonic Nanostructures for Surface-Enhanced Raman Scattering Application,” ACS Appl. Mater. Interfaces 7(31), 17247–17254 (2015).
    [Crossref]
  17. Z. Yin, Y. F. Geng, Q. L. Xie, X. M. Hong, X. L. Tan, Y. Z. Chen, L. L. Wang, W. J. Wang, and X. J. Li, “Photoreduced silver nanoparticles grown on femtosecond laser ablated, D-shaped fiber probe for surface-enhanced Raman scattering,” Appl. Opt. 55(20), 5408–5412 (2016).
    [Crossref]
  18. E. J. Smythe, M. D. Dickey, J. M. Bao, G. M. Whitesides, and F. Capasso, “Optical Antenna Arrays on a Fiber Facet for in Situ Surface-Enhanced Raman Scattering Detection,” Nano Lett. 9(3), 1132–1138 (2009).
    [Crossref]
  19. A. Ali, E. Y. Hwang, J. Choo, and D. W. Lim, “PEGylated nanographene-mediated metallic nanoparticle clusters for surface enhanced Raman scattering-based biosensing,” Analyst 143(11), 2604–2615 (2018).
    [Crossref]
  20. A. Khaleque, E. G. Mironov, J. H. Osorio, Z. Y. Li, C. M. B. Cordeiro, L. M. Liu, M. A. R. Franco, J. L. Liow, and H. T. Hattori, “Integration of bow-tie plasmonic nano-antennas on tapered fibers,” Opt. Express 25(8), 8986–8996 (2017).
    [Crossref]
  21. F. L. Yap, P. Thoniyot, S. Krishnan, and S. Krishnamoorthy, “Nanoparticle Cluster Arrays for High-Performance SERS through Directed Self-Assembly on Flat Substrates and on Optical Fibers,” ACS Nano 6(3), 2056–2070 (2012).
    [Crossref]
  22. P. Vaiano, B. Carotenuto, M. Pisco, A. Ricciardi, G. Quero, M. Consales, A. Crescitelli, E. Esposito, and A. Cusano, “Lab on Fiber Technology for biological sensing applications,” Laser Photonics Rev. 10(6), 922–961 (2016).
    [Crossref]
  23. E. D. Palik, Handbook of Optical Constants of Solids (Academic, 1997).
  24. P. H. Qiu, C. Jensen, N. Charity, R. Towner, and C. B. Mao, “Oil Phase Evaporation-Induced Self-Assembly of Hydrophobic Nanoparticles into Spherical Clusters with Controlled Surface Chemistry in an Oil-in-Water Dispersion and Comparison of Behaviors of Individual and Clustered Iron Oxide Nanoparticles,” J. Am. Chem. Soc. 132(50), 17724–17732 (2010).
    [Crossref]
  25. J. Xu, J. F. Xia, and Z. Q. Lin, “Evaporation-induced self-assembly of nanoparticles from a sphere-on-flat geometry,” Angew. Chem. Int. Ed. 46(11), 1860–1863 (2007).
    [Crossref]
  26. R. D. Deegan, O. Bakajin, T. F. Dupont, G. Huber, S. R. Nagel, and T. A. Witten, “Capillary flow as the cause of ring stains from dried liquid drops,” Nature 389(6653), 827–829 (1997).
    [Crossref]
  27. X. Y. Shen, C. M. Ho, and T. S. Wong, “Minimal Size of Coffee Ring Structure,” J. Phys. Chem. B 114(16), 5269–5274 (2010).
    [Crossref]
  28. P. J. Yunker, T. Still, M. A. Lohr, and A. G. Yodh, “Suppression of the coffee-ring effect by shape-dependent capillary interactions,” Nature 476(7360), 308–311 (2011).
    [Crossref]
  29. H. Hu and R. G. Larson, “Marangoni Effect Reverses Coffee-Ring Depositions,” J. Phys. Chem. B 110(14), 7090–7094 (2006).
    [Crossref]
  30. S. K. Yang, X. M. Dai, B. B. Stogin, and T. S. Wong, “Ultrasensitive surface-enhanced Raman scattering detection in common fluids,” Proc. Natl. Acad. Sci. U. S. A. 113(2), 268–273 (2016).
    [Crossref]
  31. K. Okamoto, Fundamentals of Optical Waveguides 2nd Edition (Academic, 2005).
  32. Q. Zhang, Y. F. Yuan, C. P. Wang, Z. J. Zhou, L. Li, S. J. Zhang, and J. H. Xu, “Design considerations for SERS detection in colloidal solution: reduce spectral intensity fluctuation,” J. Raman Spectrosc. 47(4), 395–401 (2016).
    [Crossref]
  33. K. B. Zhang, T. X. Zeng, X. L. Tan, W. D. Wu, Y. J. Tang, and H. B. Zhang, “A facile surface-enhanced Raman scattering (SERS) detection of rhodamine 6G and crystal violet using Au nanoparticle substrates,” Appl. Surf. Sci. 347, 569–573 (2015).
    [Crossref]
  34. Y. Ran, P. Strobbia, V. Cupil-Garcia, and T. Vo-Dinh, “Fiber-optrode SERS probes using plasmonic silver-coated gold nanostars,” Sens. Actuators, B 287, 95–101 (2019).
    [Crossref]
  35. P. L. Stiles, J. A. Dieringer, N. C. Shah, and R. R. Van Duyne, “Surface-Enhanced Raman Spectroscopy,” Annu. Rev. Anal. Chem. 1(1), 601–626 (2008).
    [Crossref]
  36. D. J. Alderman, “Malachite green: a review,” J. Fish Dis. 8(3), 289–298 (1985).
    [Crossref]
  37. J. C. Hashimoto, J. A. R. Paschoal, J. F. de Queiroz, and F. G. R. Reyes, “Considerations on the Use of Malachite Green in Aquaculture and Analytical Aspects of Determining the Residues in Fish: A Review,” J. Aquat. Food Prod. Technol. 20(3), 273–294 (2011).
    [Crossref]
  38. J. B. Lee, H. Y. Kim, Y. M. Jang, J. Y. Song, S. M. Woo, M. S. Park, H. S. Lee, S. K. Lee, and M. Kim, “Determination of malachite green and crystal violet in processed fish products,” Food Addit. Contam., Part A 27(7), 953–961 (2010).
    [Crossref]

2019 (4)

Y. Liu, F. Zhou, H. Wang, X. Huang, and D. Ling, “Micro-coffee-ring-patterned fiber SERS probes and their in situ detection application in complex liquid environments,” Sens. Actuators, B 299, 126990 (2019).
[Crossref]

Y. Liu, J. Y. Guang, C. Liu, S. Bi, Q. Liu, P. Li, N. Zhang, S. M. Chen, H. Z. Yuan, D. P. Zhou, and W. Peng, “Simple and Low-Cost Plasmonic Fiber-Optic Probe as SERS and Biosensing Platform,” Adv. Opt. Mater. 7(19), 1900337 (2019).
[Crossref]

V. Tran, B. Walkenfort, M. Konig, M. Salehi, and S. Schlucker, “Rapid, Quantitative, and Ultrasensitive Point-of-Care Testing: A Portable SERS Reader for Lateral Flow Assays in Clinical Chemistry,” Angew. Chem. Int. Ed. 58(2), 442–446 (2019).
[Crossref]

Y. Ran, P. Strobbia, V. Cupil-Garcia, and T. Vo-Dinh, “Fiber-optrode SERS probes using plasmonic silver-coated gold nanostars,” Sens. Actuators, B 287, 95–101 (2019).
[Crossref]

2018 (4)

A. Ali, E. Y. Hwang, J. Choo, and D. W. Lim, “PEGylated nanographene-mediated metallic nanoparticle clusters for surface enhanced Raman scattering-based biosensing,” Analyst 143(11), 2604–2615 (2018).
[Crossref]

C. G. Danny, A. Subrahmanyam, and V. V. R. Sai, “Development of plasmonic U-bent plastic optical fiber probes for surface enhanced Raman scattering based biosensing,” J. Raman Spectrosc. 49(10), 1607–1616 (2018).
[Crossref]

R. Panneerselvam, G. K. Liu, Y. H. Wang, J. Y. Liu, S. Y. Ding, J. F. Li, D. Y. Wu, and Z. Q. Tian, “Surface-enhanced Raman spectroscopy: bottlenecks and future directions,” Chem. Commun. 54(1), 10–25 (2018).
[Crossref]

T. Hutter, S. R. Elliott, and S. Mahajan, “Optical fibre-tip probes for SERS: numerical study for design considerations,” Opt. Express 26(12), 15539–15550 (2018).
[Crossref]

2017 (2)

2016 (6)

Y. Liu, Z. L. Huang, F. Zhou, X. Lei, B. Yao, G. W. Meng, and Q. H. Mao, “Highly sensitive fibre surface-enhanced Raman scattering probes fabricated using laser-induced self-assembly in a meniscus,” Nanoscale 8(20), 10607–10614 (2016).
[Crossref]

P. Vaiano, B. Carotenuto, M. Pisco, A. Ricciardi, G. Quero, M. Consales, A. Crescitelli, E. Esposito, and A. Cusano, “Lab on Fiber Technology for biological sensing applications,” Laser Photonics Rev. 10(6), 922–961 (2016).
[Crossref]

S. K. Yang, X. M. Dai, B. B. Stogin, and T. S. Wong, “Ultrasensitive surface-enhanced Raman scattering detection in common fluids,” Proc. Natl. Acad. Sci. U. S. A. 113(2), 268–273 (2016).
[Crossref]

Q. Zhang, Y. F. Yuan, C. P. Wang, Z. J. Zhou, L. Li, S. J. Zhang, and J. H. Xu, “Design considerations for SERS detection in colloidal solution: reduce spectral intensity fluctuation,” J. Raman Spectrosc. 47(4), 395–401 (2016).
[Crossref]

Z. Yin, Y. F. Geng, Q. L. Xie, X. M. Hong, X. L. Tan, Y. Z. Chen, L. L. Wang, W. J. Wang, and X. J. Li, “Photoreduced silver nanoparticles grown on femtosecond laser ablated, D-shaped fiber probe for surface-enhanced Raman scattering,” Appl. Opt. 55(20), 5408–5412 (2016).
[Crossref]

G. K. Pandey, N. K. Pathak, A. Ji, H. Pathak, and R. P. Sharma, “Study of Surface Enhanced Raman Scattering of Single Molecule Adsorbed on the Surface of Metal Nanogeometries: Electrostatic Approach,” Plasmonics 11(5), 1343–1349 (2016).
[Crossref]

2015 (4)

J. Song, J. H. Xian, M. H. Yu, D. Wang, S. Ye, H. B. Niu, X. Peng, and J. L. Qu, “Ultrahigh Enhancement Factor by Using a Silver Nanoshell With a Gain Core Above a Silver Substrate for Surface-Enhanced Raman Scattering at the Single-Molecule Level,” IEEE Photonics J. 7(5), 1–8 (2015).
[Crossref]

Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
[Crossref]

Z. L. Huang, X. Lei, Y. Liu, Z. W. Wang, X. J. Wang, Z. M. Wang, Q. H. Mao, and G. W. Meng, “Tapered Optical Fiber Probe Assembled with Plasmonic Nanostructures for Surface-Enhanced Raman Scattering Application,” ACS Appl. Mater. Interfaces 7(31), 17247–17254 (2015).
[Crossref]

K. B. Zhang, T. X. Zeng, X. L. Tan, W. D. Wu, Y. J. Tang, and H. B. Zhang, “A facile surface-enhanced Raman scattering (SERS) detection of rhodamine 6G and crystal violet using Au nanoparticle substrates,” Appl. Surf. Sci. 347, 569–573 (2015).
[Crossref]

2014 (1)

M. Pisco, F. Galeotti, G. Quero, A. Iadicicco, M. Giordano, and A. Cusano, “Miniaturized Sensing Probes Based on Metallic Dielectric Crystals Self-Assembled on Optical Fiber Tips,” ACS Photonics 1(10), 917–927 (2014).
[Crossref]

2012 (2)

B. Sharma, R. R. Frontiera, A. I. Henry, E. Ringe, and R. P. Van Duyne, “SERS: Materials, applications, and the future,” Mater. Today 15(1-2), 16–25 (2012).
[Crossref]

F. L. Yap, P. Thoniyot, S. Krishnan, and S. Krishnamoorthy, “Nanoparticle Cluster Arrays for High-Performance SERS through Directed Self-Assembly on Flat Substrates and on Optical Fibers,” ACS Nano 6(3), 2056–2070 (2012).
[Crossref]

2011 (3)

P. J. Yunker, T. Still, M. A. Lohr, and A. G. Yodh, “Suppression of the coffee-ring effect by shape-dependent capillary interactions,” Nature 476(7360), 308–311 (2011).
[Crossref]

J. C. Hashimoto, J. A. R. Paschoal, J. F. de Queiroz, and F. G. R. Reyes, “Considerations on the Use of Malachite Green in Aquaculture and Analytical Aspects of Determining the Residues in Fish: A Review,” J. Aquat. Food Prod. Technol. 20(3), 273–294 (2011).
[Crossref]

Y. Zhu, R. A. Dluhy, and Y. P. Zhao, “Development of silver nanorod array based fiber optic probes for SERS detection,” Sens. Actuators, B 157(1), 42–50 (2011).
[Crossref]

2010 (3)

J. B. Lee, H. Y. Kim, Y. M. Jang, J. Y. Song, S. M. Woo, M. S. Park, H. S. Lee, S. K. Lee, and M. Kim, “Determination of malachite green and crystal violet in processed fish products,” Food Addit. Contam., Part A 27(7), 953–961 (2010).
[Crossref]

X. Y. Shen, C. M. Ho, and T. S. Wong, “Minimal Size of Coffee Ring Structure,” J. Phys. Chem. B 114(16), 5269–5274 (2010).
[Crossref]

P. H. Qiu, C. Jensen, N. Charity, R. Towner, and C. B. Mao, “Oil Phase Evaporation-Induced Self-Assembly of Hydrophobic Nanoparticles into Spherical Clusters with Controlled Surface Chemistry in an Oil-in-Water Dispersion and Comparison of Behaviors of Individual and Clustered Iron Oxide Nanoparticles,” J. Am. Chem. Soc. 132(50), 17724–17732 (2010).
[Crossref]

2009 (1)

E. J. Smythe, M. D. Dickey, J. M. Bao, G. M. Whitesides, and F. Capasso, “Optical Antenna Arrays on a Fiber Facet for in Situ Surface-Enhanced Raman Scattering Detection,” Nano Lett. 9(3), 1132–1138 (2009).
[Crossref]

2008 (1)

P. L. Stiles, J. A. Dieringer, N. C. Shah, and R. R. Van Duyne, “Surface-Enhanced Raman Spectroscopy,” Annu. Rev. Anal. Chem. 1(1), 601–626 (2008).
[Crossref]

2007 (1)

J. Xu, J. F. Xia, and Z. Q. Lin, “Evaporation-induced self-assembly of nanoparticles from a sphere-on-flat geometry,” Angew. Chem. Int. Ed. 46(11), 1860–1863 (2007).
[Crossref]

2006 (2)

1997 (1)

R. D. Deegan, O. Bakajin, T. F. Dupont, G. Huber, S. R. Nagel, and T. A. Witten, “Capillary flow as the cause of ring stains from dried liquid drops,” Nature 389(6653), 827–829 (1997).
[Crossref]

1985 (1)

D. J. Alderman, “Malachite green: a review,” J. Fish Dis. 8(3), 289–298 (1985).
[Crossref]

Alderman, D. J.

D. J. Alderman, “Malachite green: a review,” J. Fish Dis. 8(3), 289–298 (1985).
[Crossref]

Ali, A.

A. Ali, E. Y. Hwang, J. Choo, and D. W. Lim, “PEGylated nanographene-mediated metallic nanoparticle clusters for surface enhanced Raman scattering-based biosensing,” Analyst 143(11), 2604–2615 (2018).
[Crossref]

Bakajin, O.

R. D. Deegan, O. Bakajin, T. F. Dupont, G. Huber, S. R. Nagel, and T. A. Witten, “Capillary flow as the cause of ring stains from dried liquid drops,” Nature 389(6653), 827–829 (1997).
[Crossref]

Bao, J. M.

E. J. Smythe, M. D. Dickey, J. M. Bao, G. M. Whitesides, and F. Capasso, “Optical Antenna Arrays on a Fiber Facet for in Situ Surface-Enhanced Raman Scattering Detection,” Nano Lett. 9(3), 1132–1138 (2009).
[Crossref]

Baumberg, J. J.

Bi, S.

Y. Liu, J. Y. Guang, C. Liu, S. Bi, Q. Liu, P. Li, N. Zhang, S. M. Chen, H. Z. Yuan, D. P. Zhou, and W. Peng, “Simple and Low-Cost Plasmonic Fiber-Optic Probe as SERS and Biosensing Platform,” Adv. Opt. Mater. 7(19), 1900337 (2019).
[Crossref]

Capasso, F.

E. J. Smythe, M. D. Dickey, J. M. Bao, G. M. Whitesides, and F. Capasso, “Optical Antenna Arrays on a Fiber Facet for in Situ Surface-Enhanced Raman Scattering Detection,” Nano Lett. 9(3), 1132–1138 (2009).
[Crossref]

Carotenuto, B.

P. Vaiano, B. Carotenuto, M. Pisco, A. Ricciardi, G. Quero, M. Consales, A. Crescitelli, E. Esposito, and A. Cusano, “Lab on Fiber Technology for biological sensing applications,” Laser Photonics Rev. 10(6), 922–961 (2016).
[Crossref]

Charity, N.

P. H. Qiu, C. Jensen, N. Charity, R. Towner, and C. B. Mao, “Oil Phase Evaporation-Induced Self-Assembly of Hydrophobic Nanoparticles into Spherical Clusters with Controlled Surface Chemistry in an Oil-in-Water Dispersion and Comparison of Behaviors of Individual and Clustered Iron Oxide Nanoparticles,” J. Am. Chem. Soc. 132(50), 17724–17732 (2010).
[Crossref]

Charlton, M. D. B.

Chen, J.

Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
[Crossref]

Chen, S. M.

Y. Liu, J. Y. Guang, C. Liu, S. Bi, Q. Liu, P. Li, N. Zhang, S. M. Chen, H. Z. Yuan, D. P. Zhou, and W. Peng, “Simple and Low-Cost Plasmonic Fiber-Optic Probe as SERS and Biosensing Platform,” Adv. Opt. Mater. 7(19), 1900337 (2019).
[Crossref]

Chen, Y. Z.

Choo, J.

A. Ali, E. Y. Hwang, J. Choo, and D. W. Lim, “PEGylated nanographene-mediated metallic nanoparticle clusters for surface enhanced Raman scattering-based biosensing,” Analyst 143(11), 2604–2615 (2018).
[Crossref]

Consales, M.

P. Vaiano, B. Carotenuto, M. Pisco, A. Ricciardi, G. Quero, M. Consales, A. Crescitelli, E. Esposito, and A. Cusano, “Lab on Fiber Technology for biological sensing applications,” Laser Photonics Rev. 10(6), 922–961 (2016).
[Crossref]

Cordeiro, C. M. B.

Crescitelli, A.

P. Vaiano, B. Carotenuto, M. Pisco, A. Ricciardi, G. Quero, M. Consales, A. Crescitelli, E. Esposito, and A. Cusano, “Lab on Fiber Technology for biological sensing applications,” Laser Photonics Rev. 10(6), 922–961 (2016).
[Crossref]

Cui, L.

Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
[Crossref]

Cupil-Garcia, V.

Y. Ran, P. Strobbia, V. Cupil-Garcia, and T. Vo-Dinh, “Fiber-optrode SERS probes using plasmonic silver-coated gold nanostars,” Sens. Actuators, B 287, 95–101 (2019).
[Crossref]

Cusano, A.

P. Vaiano, B. Carotenuto, M. Pisco, A. Ricciardi, G. Quero, M. Consales, A. Crescitelli, E. Esposito, and A. Cusano, “Lab on Fiber Technology for biological sensing applications,” Laser Photonics Rev. 10(6), 922–961 (2016).
[Crossref]

M. Pisco, F. Galeotti, G. Quero, A. Iadicicco, M. Giordano, and A. Cusano, “Miniaturized Sensing Probes Based on Metallic Dielectric Crystals Self-Assembled on Optical Fiber Tips,” ACS Photonics 1(10), 917–927 (2014).
[Crossref]

Dai, X. M.

S. K. Yang, X. M. Dai, B. B. Stogin, and T. S. Wong, “Ultrasensitive surface-enhanced Raman scattering detection in common fluids,” Proc. Natl. Acad. Sci. U. S. A. 113(2), 268–273 (2016).
[Crossref]

Danny, C. G.

C. G. Danny, A. Subrahmanyam, and V. V. R. Sai, “Development of plasmonic U-bent plastic optical fiber probes for surface enhanced Raman scattering based biosensing,” J. Raman Spectrosc. 49(10), 1607–1616 (2018).
[Crossref]

de Queiroz, J. F.

J. C. Hashimoto, J. A. R. Paschoal, J. F. de Queiroz, and F. G. R. Reyes, “Considerations on the Use of Malachite Green in Aquaculture and Analytical Aspects of Determining the Residues in Fish: A Review,” J. Aquat. Food Prod. Technol. 20(3), 273–294 (2011).
[Crossref]

Deegan, R. D.

R. D. Deegan, O. Bakajin, T. F. Dupont, G. Huber, S. R. Nagel, and T. A. Witten, “Capillary flow as the cause of ring stains from dried liquid drops,” Nature 389(6653), 827–829 (1997).
[Crossref]

Dickey, M. D.

E. J. Smythe, M. D. Dickey, J. M. Bao, G. M. Whitesides, and F. Capasso, “Optical Antenna Arrays on a Fiber Facet for in Situ Surface-Enhanced Raman Scattering Detection,” Nano Lett. 9(3), 1132–1138 (2009).
[Crossref]

Dieringer, J. A.

P. L. Stiles, J. A. Dieringer, N. C. Shah, and R. R. Van Duyne, “Surface-Enhanced Raman Spectroscopy,” Annu. Rev. Anal. Chem. 1(1), 601–626 (2008).
[Crossref]

Ding, S. Y.

R. Panneerselvam, G. K. Liu, Y. H. Wang, J. Y. Liu, S. Y. Ding, J. F. Li, D. Y. Wu, and Z. Q. Tian, “Surface-enhanced Raman spectroscopy: bottlenecks and future directions,” Chem. Commun. 54(1), 10–25 (2018).
[Crossref]

Dluhy, R. A.

Y. Zhu, R. A. Dluhy, and Y. P. Zhao, “Development of silver nanorod array based fiber optic probes for SERS detection,” Sens. Actuators, B 157(1), 42–50 (2011).
[Crossref]

Dupont, T. F.

R. D. Deegan, O. Bakajin, T. F. Dupont, G. Huber, S. R. Nagel, and T. A. Witten, “Capillary flow as the cause of ring stains from dried liquid drops,” Nature 389(6653), 827–829 (1997).
[Crossref]

Elliott, S. R.

Esposito, E.

P. Vaiano, B. Carotenuto, M. Pisco, A. Ricciardi, G. Quero, M. Consales, A. Crescitelli, E. Esposito, and A. Cusano, “Lab on Fiber Technology for biological sensing applications,” Laser Photonics Rev. 10(6), 922–961 (2016).
[Crossref]

Feng, S. F.

Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
[Crossref]

Franco, M. A. R.

Frontiera, R. R.

B. Sharma, R. R. Frontiera, A. I. Henry, E. Ringe, and R. P. Van Duyne, “SERS: Materials, applications, and the future,” Mater. Today 15(1-2), 16–25 (2012).
[Crossref]

Galeotti, F.

M. Pisco, F. Galeotti, G. Quero, A. Iadicicco, M. Giordano, and A. Cusano, “Miniaturized Sensing Probes Based on Metallic Dielectric Crystals Self-Assembled on Optical Fiber Tips,” ACS Photonics 1(10), 917–927 (2014).
[Crossref]

Geng, Y. F.

Giordano, M.

M. Pisco, F. Galeotti, G. Quero, A. Iadicicco, M. Giordano, and A. Cusano, “Miniaturized Sensing Probes Based on Metallic Dielectric Crystals Self-Assembled on Optical Fiber Tips,” ACS Photonics 1(10), 917–927 (2014).
[Crossref]

Guang, J. Y.

Y. Liu, J. Y. Guang, C. Liu, S. Bi, Q. Liu, P. Li, N. Zhang, S. M. Chen, H. Z. Yuan, D. P. Zhou, and W. Peng, “Simple and Low-Cost Plasmonic Fiber-Optic Probe as SERS and Biosensing Platform,” Adv. Opt. Mater. 7(19), 1900337 (2019).
[Crossref]

Han, P.

Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
[Crossref]

Hashimoto, J. C.

J. C. Hashimoto, J. A. R. Paschoal, J. F. de Queiroz, and F. G. R. Reyes, “Considerations on the Use of Malachite Green in Aquaculture and Analytical Aspects of Determining the Residues in Fish: A Review,” J. Aquat. Food Prod. Technol. 20(3), 273–294 (2011).
[Crossref]

Hattori, H. T.

Henry, A. I.

B. Sharma, R. R. Frontiera, A. I. Henry, E. Ringe, and R. P. Van Duyne, “SERS: Materials, applications, and the future,” Mater. Today 15(1-2), 16–25 (2012).
[Crossref]

Ho, C. M.

X. Y. Shen, C. M. Ho, and T. S. Wong, “Minimal Size of Coffee Ring Structure,” J. Phys. Chem. B 114(16), 5269–5274 (2010).
[Crossref]

Hong, X. M.

Hu, H.

H. Hu and R. G. Larson, “Marangoni Effect Reverses Coffee-Ring Depositions,” J. Phys. Chem. B 110(14), 7090–7094 (2006).
[Crossref]

Huang, X.

Y. Liu, F. Zhou, H. Wang, X. Huang, and D. Ling, “Micro-coffee-ring-patterned fiber SERS probes and their in situ detection application in complex liquid environments,” Sens. Actuators, B 299, 126990 (2019).
[Crossref]

Huang, Z. L.

Y. Liu, Z. L. Huang, F. Zhou, X. Lei, B. Yao, G. W. Meng, and Q. H. Mao, “Highly sensitive fibre surface-enhanced Raman scattering probes fabricated using laser-induced self-assembly in a meniscus,” Nanoscale 8(20), 10607–10614 (2016).
[Crossref]

Z. L. Huang, X. Lei, Y. Liu, Z. W. Wang, X. J. Wang, Z. M. Wang, Q. H. Mao, and G. W. Meng, “Tapered Optical Fiber Probe Assembled with Plasmonic Nanostructures for Surface-Enhanced Raman Scattering Application,” ACS Appl. Mater. Interfaces 7(31), 17247–17254 (2015).
[Crossref]

Huber, G.

R. D. Deegan, O. Bakajin, T. F. Dupont, G. Huber, S. R. Nagel, and T. A. Witten, “Capillary flow as the cause of ring stains from dried liquid drops,” Nature 389(6653), 827–829 (1997).
[Crossref]

Hutter, T.

Hwang, E. Y.

A. Ali, E. Y. Hwang, J. Choo, and D. W. Lim, “PEGylated nanographene-mediated metallic nanoparticle clusters for surface enhanced Raman scattering-based biosensing,” Analyst 143(11), 2604–2615 (2018).
[Crossref]

Iadicicco, A.

M. Pisco, F. Galeotti, G. Quero, A. Iadicicco, M. Giordano, and A. Cusano, “Miniaturized Sensing Probes Based on Metallic Dielectric Crystals Self-Assembled on Optical Fiber Tips,” ACS Photonics 1(10), 917–927 (2014).
[Crossref]

Jang, Y. M.

J. B. Lee, H. Y. Kim, Y. M. Jang, J. Y. Song, S. M. Woo, M. S. Park, H. S. Lee, S. K. Lee, and M. Kim, “Determination of malachite green and crystal violet in processed fish products,” Food Addit. Contam., Part A 27(7), 953–961 (2010).
[Crossref]

Jensen, C.

P. H. Qiu, C. Jensen, N. Charity, R. Towner, and C. B. Mao, “Oil Phase Evaporation-Induced Self-Assembly of Hydrophobic Nanoparticles into Spherical Clusters with Controlled Surface Chemistry in an Oil-in-Water Dispersion and Comparison of Behaviors of Individual and Clustered Iron Oxide Nanoparticles,” J. Am. Chem. Soc. 132(50), 17724–17732 (2010).
[Crossref]

Ji, A.

G. K. Pandey, N. K. Pathak, A. Ji, H. Pathak, and R. P. Sharma, “Study of Surface Enhanced Raman Scattering of Single Molecule Adsorbed on the Surface of Metal Nanogeometries: Electrostatic Approach,” Plasmonics 11(5), 1343–1349 (2016).
[Crossref]

Khaleque, A.

Kim, H. Y.

J. B. Lee, H. Y. Kim, Y. M. Jang, J. Y. Song, S. M. Woo, M. S. Park, H. S. Lee, S. K. Lee, and M. Kim, “Determination of malachite green and crystal violet in processed fish products,” Food Addit. Contam., Part A 27(7), 953–961 (2010).
[Crossref]

Kim, M.

J. B. Lee, H. Y. Kim, Y. M. Jang, J. Y. Song, S. M. Woo, M. S. Park, H. S. Lee, S. K. Lee, and M. Kim, “Determination of malachite green and crystal violet in processed fish products,” Food Addit. Contam., Part A 27(7), 953–961 (2010).
[Crossref]

Klar, P. J.

Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
[Crossref]

Konig, M.

V. Tran, B. Walkenfort, M. Konig, M. Salehi, and S. Schlucker, “Rapid, Quantitative, and Ultrasensitive Point-of-Care Testing: A Portable SERS Reader for Lateral Flow Assays in Clinical Chemistry,” Angew. Chem. Int. Ed. 58(2), 442–446 (2019).
[Crossref]

Krishnamoorthy, S.

F. L. Yap, P. Thoniyot, S. Krishnan, and S. Krishnamoorthy, “Nanoparticle Cluster Arrays for High-Performance SERS through Directed Self-Assembly on Flat Substrates and on Optical Fibers,” ACS Nano 6(3), 2056–2070 (2012).
[Crossref]

Krishnan, S.

F. L. Yap, P. Thoniyot, S. Krishnan, and S. Krishnamoorthy, “Nanoparticle Cluster Arrays for High-Performance SERS through Directed Self-Assembly on Flat Substrates and on Optical Fibers,” ACS Nano 6(3), 2056–2070 (2012).
[Crossref]

Larson, R. G.

H. Hu and R. G. Larson, “Marangoni Effect Reverses Coffee-Ring Depositions,” J. Phys. Chem. B 110(14), 7090–7094 (2006).
[Crossref]

Lee, H. S.

J. B. Lee, H. Y. Kim, Y. M. Jang, J. Y. Song, S. M. Woo, M. S. Park, H. S. Lee, S. K. Lee, and M. Kim, “Determination of malachite green and crystal violet in processed fish products,” Food Addit. Contam., Part A 27(7), 953–961 (2010).
[Crossref]

Lee, J. B.

J. B. Lee, H. Y. Kim, Y. M. Jang, J. Y. Song, S. M. Woo, M. S. Park, H. S. Lee, S. K. Lee, and M. Kim, “Determination of malachite green and crystal violet in processed fish products,” Food Addit. Contam., Part A 27(7), 953–961 (2010).
[Crossref]

Lee, S. K.

J. B. Lee, H. Y. Kim, Y. M. Jang, J. Y. Song, S. M. Woo, M. S. Park, H. S. Lee, S. K. Lee, and M. Kim, “Determination of malachite green and crystal violet in processed fish products,” Food Addit. Contam., Part A 27(7), 953–961 (2010).
[Crossref]

Lei, X.

Y. Liu, Z. L. Huang, F. Zhou, X. Lei, B. Yao, G. W. Meng, and Q. H. Mao, “Highly sensitive fibre surface-enhanced Raman scattering probes fabricated using laser-induced self-assembly in a meniscus,” Nanoscale 8(20), 10607–10614 (2016).
[Crossref]

Z. L. Huang, X. Lei, Y. Liu, Z. W. Wang, X. J. Wang, Z. M. Wang, Q. H. Mao, and G. W. Meng, “Tapered Optical Fiber Probe Assembled with Plasmonic Nanostructures for Surface-Enhanced Raman Scattering Application,” ACS Appl. Mater. Interfaces 7(31), 17247–17254 (2015).
[Crossref]

Li, D. L.

C. Wang, L. H. Zeng, Z. Li, and D. L. Li, “Review of optical fibre probes for enhanced Raman sensing,” J. Raman Spectrosc. 48(8), 1040–1055 (2017).
[Crossref]

Li, J. F.

R. Panneerselvam, G. K. Liu, Y. H. Wang, J. Y. Liu, S. Y. Ding, J. F. Li, D. Y. Wu, and Z. Q. Tian, “Surface-enhanced Raman spectroscopy: bottlenecks and future directions,” Chem. Commun. 54(1), 10–25 (2018).
[Crossref]

Li, L.

Q. Zhang, Y. F. Yuan, C. P. Wang, Z. J. Zhou, L. Li, S. J. Zhang, and J. H. Xu, “Design considerations for SERS detection in colloidal solution: reduce spectral intensity fluctuation,” J. Raman Spectrosc. 47(4), 395–401 (2016).
[Crossref]

Li, P.

Y. Liu, J. Y. Guang, C. Liu, S. Bi, Q. Liu, P. Li, N. Zhang, S. M. Chen, H. Z. Yuan, D. P. Zhou, and W. Peng, “Simple and Low-Cost Plasmonic Fiber-Optic Probe as SERS and Biosensing Platform,” Adv. Opt. Mater. 7(19), 1900337 (2019).
[Crossref]

Li, X. J.

Li, Z.

C. Wang, L. H. Zeng, Z. Li, and D. L. Li, “Review of optical fibre probes for enhanced Raman sensing,” J. Raman Spectrosc. 48(8), 1040–1055 (2017).
[Crossref]

Li, Z. Y.

Lim, D. W.

A. Ali, E. Y. Hwang, J. Choo, and D. W. Lim, “PEGylated nanographene-mediated metallic nanoparticle clusters for surface enhanced Raman scattering-based biosensing,” Analyst 143(11), 2604–2615 (2018).
[Crossref]

Lin, Z. Q.

J. Xu, J. F. Xia, and Z. Q. Lin, “Evaporation-induced self-assembly of nanoparticles from a sphere-on-flat geometry,” Angew. Chem. Int. Ed. 46(11), 1860–1863 (2007).
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Ling, D.

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J. Xu, J. F. Xia, and Z. Q. Lin, “Evaporation-induced self-assembly of nanoparticles from a sphere-on-flat geometry,” Angew. Chem. Int. Ed. 46(11), 1860–1863 (2007).
[Crossref]

Xian, J. H.

J. Song, J. H. Xian, M. H. Yu, D. Wang, S. Ye, H. B. Niu, X. Peng, and J. L. Qu, “Ultrahigh Enhancement Factor by Using a Silver Nanoshell With a Gain Core Above a Silver Substrate for Surface-Enhanced Raman Scattering at the Single-Molecule Level,” IEEE Photonics J. 7(5), 1–8 (2015).
[Crossref]

Xie, Q. L.

Xie, Z. W.

Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
[Crossref]

Xu, J.

J. Xu, J. F. Xia, and Z. Q. Lin, “Evaporation-induced self-assembly of nanoparticles from a sphere-on-flat geometry,” Angew. Chem. Int. Ed. 46(11), 1860–1863 (2007).
[Crossref]

Xu, J. H.

Q. Zhang, Y. F. Yuan, C. P. Wang, Z. J. Zhou, L. Li, S. J. Zhang, and J. H. Xu, “Design considerations for SERS detection in colloidal solution: reduce spectral intensity fluctuation,” J. Raman Spectrosc. 47(4), 395–401 (2016).
[Crossref]

Yang, S. K.

S. K. Yang, X. M. Dai, B. B. Stogin, and T. S. Wong, “Ultrasensitive surface-enhanced Raman scattering detection in common fluids,” Proc. Natl. Acad. Sci. U. S. A. 113(2), 268–273 (2016).
[Crossref]

Yao, B.

Y. Liu, Z. L. Huang, F. Zhou, X. Lei, B. Yao, G. W. Meng, and Q. H. Mao, “Highly sensitive fibre surface-enhanced Raman scattering probes fabricated using laser-induced self-assembly in a meniscus,” Nanoscale 8(20), 10607–10614 (2016).
[Crossref]

Yap, F. L.

F. L. Yap, P. Thoniyot, S. Krishnan, and S. Krishnamoorthy, “Nanoparticle Cluster Arrays for High-Performance SERS through Directed Self-Assembly on Flat Substrates and on Optical Fibers,” ACS Nano 6(3), 2056–2070 (2012).
[Crossref]

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Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
[Crossref]

Ye, S.

J. Song, J. H. Xian, M. H. Yu, D. Wang, S. Ye, H. B. Niu, X. Peng, and J. L. Qu, “Ultrahigh Enhancement Factor by Using a Silver Nanoshell With a Gain Core Above a Silver Substrate for Surface-Enhanced Raman Scattering at the Single-Molecule Level,” IEEE Photonics J. 7(5), 1–8 (2015).
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Yin, Z.

Yodh, A. G.

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[Crossref]

Yu, M. H.

J. Song, J. H. Xian, M. H. Yu, D. Wang, S. Ye, H. B. Niu, X. Peng, and J. L. Qu, “Ultrahigh Enhancement Factor by Using a Silver Nanoshell With a Gain Core Above a Silver Substrate for Surface-Enhanced Raman Scattering at the Single-Molecule Level,” IEEE Photonics J. 7(5), 1–8 (2015).
[Crossref]

Yuan, H. Z.

Y. Liu, J. Y. Guang, C. Liu, S. Bi, Q. Liu, P. Li, N. Zhang, S. M. Chen, H. Z. Yuan, D. P. Zhou, and W. Peng, “Simple and Low-Cost Plasmonic Fiber-Optic Probe as SERS and Biosensing Platform,” Adv. Opt. Mater. 7(19), 1900337 (2019).
[Crossref]

Yuan, Y. F.

Q. Zhang, Y. F. Yuan, C. P. Wang, Z. J. Zhou, L. Li, S. J. Zhang, and J. H. Xu, “Design considerations for SERS detection in colloidal solution: reduce spectral intensity fluctuation,” J. Raman Spectrosc. 47(4), 395–401 (2016).
[Crossref]

Yunker, P. J.

P. J. Yunker, T. Still, M. A. Lohr, and A. G. Yodh, “Suppression of the coffee-ring effect by shape-dependent capillary interactions,” Nature 476(7360), 308–311 (2011).
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C. Wang, L. H. Zeng, Z. Li, and D. L. Li, “Review of optical fibre probes for enhanced Raman sensing,” J. Raman Spectrosc. 48(8), 1040–1055 (2017).
[Crossref]

Zeng, T. X.

K. B. Zhang, T. X. Zeng, X. L. Tan, W. D. Wu, Y. J. Tang, and H. B. Zhang, “A facile surface-enhanced Raman scattering (SERS) detection of rhodamine 6G and crystal violet using Au nanoparticle substrates,” Appl. Surf. Sci. 347, 569–573 (2015).
[Crossref]

Zhai, T. R.

Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
[Crossref]

Zhang, H. B.

K. B. Zhang, T. X. Zeng, X. L. Tan, W. D. Wu, Y. J. Tang, and H. B. Zhang, “A facile surface-enhanced Raman scattering (SERS) detection of rhodamine 6G and crystal violet using Au nanoparticle substrates,” Appl. Surf. Sci. 347, 569–573 (2015).
[Crossref]

Zhang, K. B.

K. B. Zhang, T. X. Zeng, X. L. Tan, W. D. Wu, Y. J. Tang, and H. B. Zhang, “A facile surface-enhanced Raman scattering (SERS) detection of rhodamine 6G and crystal violet using Au nanoparticle substrates,” Appl. Surf. Sci. 347, 569–573 (2015).
[Crossref]

Zhang, L. S.

Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
[Crossref]

Zhang, N.

Y. Liu, J. Y. Guang, C. Liu, S. Bi, Q. Liu, P. Li, N. Zhang, S. M. Chen, H. Z. Yuan, D. P. Zhou, and W. Peng, “Simple and Low-Cost Plasmonic Fiber-Optic Probe as SERS and Biosensing Platform,” Adv. Opt. Mater. 7(19), 1900337 (2019).
[Crossref]

Zhang, Q.

Q. Zhang, Y. F. Yuan, C. P. Wang, Z. J. Zhou, L. Li, S. J. Zhang, and J. H. Xu, “Design considerations for SERS detection in colloidal solution: reduce spectral intensity fluctuation,” J. Raman Spectrosc. 47(4), 395–401 (2016).
[Crossref]

Zhang, S. J.

Q. Zhang, Y. F. Yuan, C. P. Wang, Z. J. Zhou, L. Li, S. J. Zhang, and J. H. Xu, “Design considerations for SERS detection in colloidal solution: reduce spectral intensity fluctuation,” J. Raman Spectrosc. 47(4), 395–401 (2016).
[Crossref]

Zhang, Y.

Z. W. Xie, S. F. Feng, P. J. Wang, L. S. Zhang, X. Ren, L. Cui, T. R. Zhai, J. Chen, Y. L. Wang, X. K. Wang, W. F. Sun, J. S. Ye, P. Han, P. J. Klar, and Y. Zhang, “Demonstration of a 3D Radar-Like SERS Sensor Micro- and Nanofabricated on an Optical Fiber,” Adv. Opt. Mater. 3(9), 1232–1239 (2015).
[Crossref]

Zhao, Y. P.

Y. Zhu, R. A. Dluhy, and Y. P. Zhao, “Development of silver nanorod array based fiber optic probes for SERS detection,” Sens. Actuators, B 157(1), 42–50 (2011).
[Crossref]

Zhou, D. P.

Y. Liu, J. Y. Guang, C. Liu, S. Bi, Q. Liu, P. Li, N. Zhang, S. M. Chen, H. Z. Yuan, D. P. Zhou, and W. Peng, “Simple and Low-Cost Plasmonic Fiber-Optic Probe as SERS and Biosensing Platform,” Adv. Opt. Mater. 7(19), 1900337 (2019).
[Crossref]

Zhou, F.

Y. Liu, F. Zhou, H. Wang, X. Huang, and D. Ling, “Micro-coffee-ring-patterned fiber SERS probes and their in situ detection application in complex liquid environments,” Sens. Actuators, B 299, 126990 (2019).
[Crossref]

Y. Liu, Z. L. Huang, F. Zhou, X. Lei, B. Yao, G. W. Meng, and Q. H. Mao, “Highly sensitive fibre surface-enhanced Raman scattering probes fabricated using laser-induced self-assembly in a meniscus,” Nanoscale 8(20), 10607–10614 (2016).
[Crossref]

Zhou, Z. J.

Q. Zhang, Y. F. Yuan, C. P. Wang, Z. J. Zhou, L. Li, S. J. Zhang, and J. H. Xu, “Design considerations for SERS detection in colloidal solution: reduce spectral intensity fluctuation,” J. Raman Spectrosc. 47(4), 395–401 (2016).
[Crossref]

Zhu, Y.

Y. Zhu, R. A. Dluhy, and Y. P. Zhao, “Development of silver nanorod array based fiber optic probes for SERS detection,” Sens. Actuators, B 157(1), 42–50 (2011).
[Crossref]

Zoorob, M. E.

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Z. L. Huang, X. Lei, Y. Liu, Z. W. Wang, X. J. Wang, Z. M. Wang, Q. H. Mao, and G. W. Meng, “Tapered Optical Fiber Probe Assembled with Plasmonic Nanostructures for Surface-Enhanced Raman Scattering Application,” ACS Appl. Mater. Interfaces 7(31), 17247–17254 (2015).
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ACS Nano (1)

F. L. Yap, P. Thoniyot, S. Krishnan, and S. Krishnamoorthy, “Nanoparticle Cluster Arrays for High-Performance SERS through Directed Self-Assembly on Flat Substrates and on Optical Fibers,” ACS Nano 6(3), 2056–2070 (2012).
[Crossref]

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[Crossref]

Y. Liu, J. Y. Guang, C. Liu, S. Bi, Q. Liu, P. Li, N. Zhang, S. M. Chen, H. Z. Yuan, D. P. Zhou, and W. Peng, “Simple and Low-Cost Plasmonic Fiber-Optic Probe as SERS and Biosensing Platform,” Adv. Opt. Mater. 7(19), 1900337 (2019).
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V. Tran, B. Walkenfort, M. Konig, M. Salehi, and S. Schlucker, “Rapid, Quantitative, and Ultrasensitive Point-of-Care Testing: A Portable SERS Reader for Lateral Flow Assays in Clinical Chemistry,” Angew. Chem. Int. Ed. 58(2), 442–446 (2019).
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J. Xu, J. F. Xia, and Z. Q. Lin, “Evaporation-induced self-assembly of nanoparticles from a sphere-on-flat geometry,” Angew. Chem. Int. Ed. 46(11), 1860–1863 (2007).
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Appl. Opt. (1)

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K. B. Zhang, T. X. Zeng, X. L. Tan, W. D. Wu, Y. J. Tang, and H. B. Zhang, “A facile surface-enhanced Raman scattering (SERS) detection of rhodamine 6G and crystal violet using Au nanoparticle substrates,” Appl. Surf. Sci. 347, 569–573 (2015).
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Chem. Commun. (1)

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J. Song, J. H. Xian, M. H. Yu, D. Wang, S. Ye, H. B. Niu, X. Peng, and J. L. Qu, “Ultrahigh Enhancement Factor by Using a Silver Nanoshell With a Gain Core Above a Silver Substrate for Surface-Enhanced Raman Scattering at the Single-Molecule Level,” IEEE Photonics J. 7(5), 1–8 (2015).
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C. Wang, L. H. Zeng, Z. Li, and D. L. Li, “Review of optical fibre probes for enhanced Raman sensing,” J. Raman Spectrosc. 48(8), 1040–1055 (2017).
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Figures (9)

Fig. 1.
Fig. 1. Experimental setup of the laser-induced evaporation self-assembly method.
Fig. 2.
Fig. 2. SEM image of fiber facets with different dip-coating cycles: (a) 5 cycles (b) 10 cycles (c) 15 cycles, and (d) 20 cycles. Some of the newly-formed clusters are marked with red circles.
Fig. 3.
Fig. 3. Schematic diagram of the nanocluster formation. (a)–(c) The seeding stage: as the solvent in the colloid droplet eventually evaporates, the Au nanorods within the droplet are deposited onto the fiber facet nearly monodispersely; (d)–(f) The growing stage: as the deposited nanoparticles gradually accumulate, when the droplet thickness becomes comparable with the radius of local high temperature region near the seeds on the optical fiber facet, the local high temperature near the seeds may greatly affect the evaporation rates at different locations on the droplet surface, e.g. the evaporation on the points above the cluster seeds occurs faster than it does elsewhere (g), and finally causing the formation of cluster structures.
Fig. 4.
Fig. 4. (a) The SEM image of optical fiber SERS probes fabricated without laser irradiation. The dipping-pulling cycle is 15. (b) SERS spectra of R6G solution obtained by optical fiber SERS probes fabricated with (black line) and without (red line) laser irradiation.
Fig. 5.
Fig. 5. (a) The SERS spectra of R6G aqueous solution measured by optical fiber SERS probes fabricated with different dipping-pulling cycles; (b) The change in SERS intensity of the Raman peak at 1508 cm-1 with the number of dipping-pulling cycles.
Fig. 6.
Fig. 6. The detection reproducibility of Au-nanorod-clusters patterned fiber SERS probes: (a) SERS spectra of 10−8 M R6G solution measured by ten fiber SERS probes (b) SERS intensities obtained from (a), for peaks at 1182 cm-1, 1313 cm-1, and 1508 cm-1.
Fig. 7.
Fig. 7. (a) SERS spectra of R6G solutions with concentration of 10−7 M to 10−10 M, obtained with Au-nanorod-clusters patterned fiber SERS probes; (b) Comparison between the cluster patterned fiber SERS probes and typical fiber SERS probes fabricated using the chemical modification and immobilization method.
Fig. 8.
Fig. 8. Theoretical electric-field intensity distribution, calculated for (a) an Au nanorod cluster, and (b) isolated Au nanorods, respectively. The total numbers of Au nanorods are the same for both cases. For comparison, the color bar is identical for both (a) and (b).
Fig. 9.
Fig. 9. SERS spectra obtained by Au-nanorod-clusters patterned optical fiber SERS probes for (a) CV and (b) MG solutions.

Tables (1)

Tables Icon

Table 1. Evolution of the dipping-pulling process.

Metrics