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Abstract
Dopamine is a biomolecule that plays an important role in controlling brain function. The concentration of dopamine is a critical parameter in biotechnology. In the present research, a novel methodology for synthesis of a chitosan/polyaniline-gold-nanoparticle nanostructure layer by using the laser ablation technique is developed. The novel polyaniline nanostructure composite layer was coated on the surface of the photonic crystal with 28 alternating layers of SiO2 and TiO2 by an electron gun deposition machine. By implementing the reflectance set-up, a photonic crystal/chitosan/polyaniline-gold-nanoparticle was used to measure the low concentration of dopamine by the lowest concentration of dopamine set to 1 ppm. The results propose a new approach and future directions in sensor-based techniques.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
Corrections
5 April 2023: Minor corrections were made to the text.
1. Introduction
Dopamine is the main member of the catechol amine family that contains the benzene ring [1,2], and ethyl chain in the main structure. Dopamine has a main role in the brain for controlling the neuron activity and causes some neuro system damages including Parkinson [3], schizophrenia [4], attention defect hyperactivity [5], and Tourette syndrome [6,7].
The concentration of dopamine can be measured using analytical methods including liquid chromatography [8], mass spectroscopy [9], and electrophorese [10]. The optical methods, which are based on the absorption and emission of particular photon in the biomaterials, are the best candidate for spectroscopy of nephron components and measure the low concentration of dopamine. Hence, photoluminescence [11], Raman spectroscopy [12], colorimeter [13] and two photon absorption spectroscopies [14] were utilized to detect and measure the low concentration of dopamine and catechol amine family by the sensitivity in the range of 0.01-10pM. Among analytical methods, the electrochemical technique is a unique accurate and reliable method for detecting and recognizing biomolecules such as dopamine. Kıranşan et. al., investigated the amperometry method for detection of dopamine using pyronin Y in the graphene composite sheet structure to detect the dopamine [15]. The mentioned techniques for analyzing can be used to measure and analyze the dopamine, but the application of these techniques suffers from disadvantages such as the cost of the instrument, chemical knowledge, and analytical grade of dopamine for accurate calibration curve.
Moreover, the nanostructures were used to improve the sensitivity, response time, and selectivity of dopamine sensors. These nanostructures can be used to enhance the limit of detection of biosensor in the range of 200 fM-20 nM based on carbon quantum dots [16], graphene [17], tin oxide nanoparticles [18], Fe3O4 -nanoparticles [19] and gold nanocomponents [20] and also nice periodic structures, such as photonic crystals.
Photonic crystals (PCs) are periodic structures consisting of materials with different refractive indices and the photonic bandgap region as near zero group velocity spectra [21]. To use these structures as a sensor, scientists are required to manage the defect modes in the photonic band gap region based on the extra thin layer, polarization, or incidence angles. To design useful sensor with the minimum corresponding to the external parameters like as polarizations, Tamm plasmon (TP) is introduced. TP depends on the homogeneity of the medium on the border between two dielectric materials and can be observed at the interface of two Isotropic dielectrics that one of them is alternately inhomogeneous in the direction perpendicular to the boundary [20]. In the best structures, the refractive index of the dielectric that is formed before the gold layer, should be chosen in higher refractive index [22]. Unique properties of TP like as the formation of TP in transverse electric (TE) and transverse magnetic (TM) polarization modes, the excitation of TP in the normal radiation of light beam, and the generation of TP wave without the coupling tools (prism, grating and waveguide), have always attracted a lot of attention to use the TP in optical filters [23], optical switches [24], polariton laser [25], and optical sensor [26]. The dielectric loss of TP is less than the surface plasmon polariton (SPP), which it gives them advantages over SPP [25, 27] including the more stable and strong surface fields, sharper coupling, and longer propagation length. Therefore, the sensitivity [28], nonlinearity [24], and the optical properties of optical device [29] based on PC can be improved and develop using TPs. The advantages of the PC sensor and TP sensor are the simple analysis of results, flexibility in the experiment, the use of a broadband visible light source, fast response time, and no need for the complex calibration curve.
On the other hand, Polyaniline is a conductive polymer with [C6H5NH2]n chemical formula and it has more application in biosensor, solar cell, supercapacitor, drug delivery, and display devices. The polyaniline in nanoform can be synthesized using microemulsion polymerization [30], chemical polymerization of aniline (with ammonium peroxydisulfate) [31], in-situ oxidative polymerization of aniline [32]. The main advantage of polyaniline nanostructure is improving the electrical property such as higher control in conductivity which is significant parameter in the plasmonic sensor.
In this study, the 28 alternating SiO2 and TiO2 layers were fabricated to exciting the Tamm plasmon optical mode and the polyaniline nanostructure and the gold nanoparticles are synthesized using laser ablation technique in the chitosan solution to interact with analyte. The chitosan-polyaniline-nanostructure/gold-nanoparticles (Chi-PANI/Au-NPs) layer is coated on the surface of 28 layers PC after characterizing the nanostructures using Fourier transform infrared (FTIR), X-ray diffraction (XRD), UV-visible (UV-vis) spectroscopies, energy dispersive X-ray (EDX) and field emission scanning electron microscopy (FESEM), the photonic system was used to measure the low concentration of dopamine based on Tamm plasmon.
2. Materials and methods
2.1 Material
The gold, TiO2, and SiO2 targets and chemical material including chitosan, aniline, and acetic acid were purchased in analytical grade from Sigma Aldrich Company and the vial Dopamine was provided from Caspian Tamin Pharmaceutical Company.
2.2 PC construction
The PC contains 28 alternating layers of the SiO2 and TiO2 which were deposited on the surface of BK7 glass (2 mm) using electron gun deposition system. The layers were designed in such a way that the wavelength and bandwidth are 650 nm and 150 nm, respectively. In this structure, the refractive indies of SiO2 and TiO2 layers were 1.45 and 2.21, respectively, and the layers were designed with quarter wave thicknesses of the 650 nm design wavelength.
2.3 Preparation of chitosan
0.5003 g of chitosan powder have been solved in the 100 ml acetic acid (0.2 N). The chitosan powder completely solved in the acetic acid solution after 48 hours at room temperature, and the clear solution was achieved to prepare the nanocomposite. The solution at pH 1.3 was used to prepare the polyaniline nanostructure.
2.4 Preparation of polyaniline tablet
A 100 ml solution containing 0.1 M aniline in IM H2SO4 was prepared by dissolution of 20 microliter of vacuum distilled aniline. The equimolar amount of ammonium proxy disulfate was separately prepared as oxidizing reagent. The prepared solutions were mixed together using stirrer for 1 h. The powder settled after 12 hours and the solution was decantated. To purification of powder, the precipitated polyaniline powder was washed and it was separated by centrifuging at 4000 rpm for 3 minutes. The procedure was repeated for three times to obtain the pure wet polyaniline power. The final green color polyaniline tablet (PANI-Tb) was achieved after drying in oven (90°C) for 3 hours.
2.5 Preparation of dopamine
The concentration of standard vial of dopamine was in the 40 mg/ml and it was systematically dissolved in the distilled water to prepare the low concentration of dopamine including 1,3,5, and 7 ppm in the separate dish.
2.6 Laser ablation setup
The laser ablation setup was presented in the Fig. 1(a). The setup contains Nd:YAG Q-switch laser in 1064 nm, with 10 Hz reputation rate and 50 mJ energy. The laser beam focused on the target using convex lens (f = 100 mm) and the target was immersed in the chitosan solution.
Fig. 1. a) The laser ablation setup for preparation of PANI-nanostructure and Au-NPs. The setup contains Nd:YAG laser, lens, lens holder, mirror and stand, optical stand, liquid tank and target. b) The sensing layer (Chi-PANI-Au-NPs) was drop casted on the surface of PC and c) the dopamine was contacted with the sensing layer (Chi-PANI-Au-NPs).
In this experiment, at first the target of PANI was immersed in the chitosan solution and it was ablated to form the PANI nanostructure in the chitosan solution. The solution was tested analytical method to confirm that the PANI nanostructure formed in the solution. After that, the pure gold target (99.99%, Sigma Aldrich) was immersed into the mentioned solution to fabricate the gold nanoparticles (Au-NPs) in the solution contains the PANI nanostructure. The final solution was tested using UV-vis and XRD spectroscopies to confirm the formation of PANI- Au-NPs in the chitosan solution. The chitosan/PANI-Au-NPs was coated on the surface of PC from the gold coated side using drop casting method.
2.7 Preparation of the layer
The gold layer with the thickness of 30 nm was deposited on the surface of TiO2 layer using sputtering coating method before to do experiment. After that, 3 drops of Chi-PANI-Au-NPs solution (equivalent of 0.15 ml (3 × 0.05 ml)) were dropped on the surface of gold thin layer using syringe contains needle (Fig. 1(b) and 1(c)). The sensing layer (Chi-PANI-Au-NPs) was dried after 24 hours and it was ready to sense the analyte.
2.8 Optical setup
Optical setup (Fig. 2) contains the broadband light source, pinhole, two lenses, rotation stage and spectrometer. The light beam focused on the surface of PC using first lens (f = 100 mm) after passing through the pinhole, and the second lens (f = 50 mm) focused the reflected light beam from the surface of PC to the spectrometer.
Fig. 2. Optical setup contains broadband light source (Xenon lamp), fiber optics holder, pinhole, lens (100 mm) lens holder, sample holder, rotation stage, lens (50 mm), lens holder, fiber optics holder, spectrometer.
The dopamine was contacted to the PC from Chi/PANI-Au-NPs side which was placed on the rotation stage and the intensity of signals was registered for the wavelength in the range of 400 to 1000 nm at 46°. The signals were registered in the different time to obtain the variation of signal intensity with time for evaluation of response time. The experiment was repeated for different concentration of dopamine. The prepared samples were characterized using UV-visible spectroscopy (RAYLEIGH), energy dispersive X-ray (EDX, Silicon Drift 2017), Fourier transform infrared (Bruker Tensor 27), X-ray diffraction (Philips pw3710) and field emission scanning electron microscopy (FEI ESEM QUANTA 200)
In order to design the 1D photonic crystal, the thickness and the refractive index of the layer were satisfied the matrix form of Fresnel’s equation for multilayer system. The one-dimensional photonic crystal contains the non-adsorbing layer. The Fresnel’s equation can be considering when the energy is stable and the layer is uniform. When the optical path is the same for high and low reflective index media (nLdL = nHdH), The lattice follows $\lambda /4$ condition and have a quarter wave stack [33]. For a dielectric layer, the matrix is written as follows:
The optical phase ( $\delta $) is $\delta = \frac{\pi }{2} + \varepsilon $ where $\varepsilon $ is constant and very small, then the M matrix of layer obtains as follows:
1D photonic crystal contains the alternating dielectric materials; so, the structure can be written as, substrate/ H/ L/…/ L/air, in which the matrix obtained by multiplying the matrix of each layer was written as follows:3. Results and discussion
PANI has low bandgap energy which implies smooth π–π* electronic [35,36]. Figure 3 shows the UV-vis spectra of PANI nanostructure for 1, 2 and 3 mins ablation time in the chitosan solution. The main peaks appeared at 279, 282, and 285 nm and are assigned the π–π* transition of nitrogen excitation [35] belong to benzenoid segments of PANI nanostructure and the observed red shit was related to the increase of the PANI chain. The peaks at 443, 453 and 459 nm are related to shift of polariton to π* band of PANI [35,37,38]. The UV-vis spectra exhibit the localized surface plasmon resonance of gold nanoparticles (Au-NPs) at 531 and 528 nm. It confirmed that Au-NPs formed in chitosan- PANI solution in the spherical shape and the blue shift authenticated the particle size decreased by increasing the ablation time.
Figures 4(a-c) exhibit the morphology of Chi-PANI nanostructure. The FESEM image confirmed that the PANI nanostructure formed in the chitosan solution using laser ablation and the polymer chain grow up with increasing the ablation time. All the figures were achieved with the 50 K and the scale bar was 1 µm. The aggregation and low specific surface area were obtained due to drastic surface tension [35,39,40] and the large agglomeration of PANI nanostructure were generated in the chitosan solution in the range of 187.5 to 86.15$\mu $V ppm-1 cm-2 [41]. PANI nanostructures are generally formed due to ablate the polyaniline tablet [42].
Fig. 4. The FE-SEM image of PANI in the chitosan for different ablation times including a) 1 min, b) 2 mins, and c) 3 mins. d) the EDX spectrum, e) the analysis area for achievement the EDX spectrum, f) FESEM of Chi-PANI-Au-NPs for 3 mins, g) analysis the FESEM image and the XRD spectra of h) PANI nanostructure and i) PANI-Au-NPs nanocomposite.
Figure 4(d) show EDX spectrum and the main peaks confirmed that the Au, N, O and S are present in the composite. The weight percentage for C, N, O and Au are 16.11%, 4.31%, 26% and 52.68%, respectively at the red point in Fig. 4(e). Figure 4(f) shows the morphology of Au-NPs in 3 mins ablation time and Fig. 4(g) depicts the FESEM image analyzed using Image J software ver.2. The FESEM image authenticated the Au-NPs were distributed in the spherical shape on the surface of Chi-PANI nanostructure and the particle size is about 50 nm.
Figure 4(h) depicts the XRD spectrum for PANI nanostructure and the analysis results were sorted in Table 1. As a result, the main peaks appeared at 8.8°, 17.71°, 26.80°, and 35.87°. d-spacing was obtained from Debye–Scherrer equation, $n\lambda = 2dsin\theta $, using the Bragg relation [43]. Where n, $\lambda $, d are an integer, the wavelength (Cu target is 1.54 Å) of the X-ray, and d-spacing which is the distance among the planes. θ is the angle between the diffraction plans and path of X-ray. The d spacing, FWHM have been listed in the Table 1 for mentioned peaks. The broad peak in the range of 20°-30° is related to chitosan and the sharp peak at 8.81° assigned the acetic acid molecules [44] as a solution for chitosan in the tunnels between the PANI chains. The peak at 17.71° and 26.80° indicates the inter-chain distance between adjoining benzene rings in PANI, and the dispersion of PANI chains at an interplanar distance [45]. The peaks at 36.58°, 44.41°, and 66.85° are corresponded the crystalline structure of Au-NPs (Fig. 4(i)). The peaks assigned the standard crystalline Bragg plans including (111), (200), and (220) and the peaks confirmed the Au nanoparticles formed in the face centers cubic lattice [46].
Table 1. The pertinent parameter for XRD spectra for PANI and PANI-Au-NPs
Figure 5 depicts the FTIR spectra for Chi-PANI nanostructure, Chi-PANI-Au-NPs, respectively. The main and significant peaks occurred at 3423.45, 3352.09, 3236.36, 2941.27, 2925.84, 2642.32, 1625.90, 1622.04, 1527.53, 1500.53, 1379.02, 1346.23, 1288.37, 1174.58, 1149.50, 1114.79, 1082.00, 1080.07, 1012.57, 939.28, 877.56, 815.84, 752.19, 613.32, 601.75, 555.46, and 441.67 cm-1. The peaks at 3423.45, 3352.09 and 3236.37 cm-1 assigned the O-H, symmetric and asymmetric NH2 and N-H stretching of PANI and chitosan that overlapped together in the chitosan solution. The peaks at 2925.84, 2941.27 cm-1 related to C-H in the chitosan [47] and aromatic aniline ring of PANI. As a result, the peak at 2925.84 cm-1 shifted to 2942.27 cm-1 which caused the interact with the dopamine and the peak at 2642.32 cm-1 shows the amide group in dopamine which appeared in the FTIR spectrum (Fig. 7(b)) after integration of Chi-PANI-Au-NPs. The N-H and the C-O stretching in the chitosan confirmed with the peaks at 1625.90 and 1622.04 cm-1. The strong peaks at 1527.53, 1500.53 cm-1 correspond to C = C quinoid ring stretching of PANI. The peak at 1471.60 cm-1 correspond to C-H bending of aromatic group in the dopamine [48]. The peaks at 1379.02 and 1346.23 cm-1 assigned the C-N stretching of benzenoid ring and CH2-OH binding in the chitosan [46] structure, respectively. The peaks at 1082, 1080.07, 613.32, and 601.75 cm-1 related to C-O-C stretching, ortho substitutions, 1,2 di-substitution in benzene ring of chitosan and PANI structures, respectively. The peaks at 441.67 and 555.46 cm-1 are the finger print of Au nanoparticles and due to the interaction of dopamine with layer, the peak is shifted from 441.67 to 555.46 cm-1. Other peaks at 1174.58, 1149.50, 1114.79, 1012.57, 939.28, 877.56, 815.84, 752.19 cm-1 relate to C-O, C-H, and C = O functional group of dopamine that appeared at the FTIR spectrum after interaction of dopamine with the Chi-PANI-Au-NPs. The peak shift in the functional group of C-O and N-H confirmed the interaction of dopamine with the Chi-PANI-Au-NPs.
Fig. 5. The FTIR spectra for a) before and b) after the contacting of Chi-PANI-Au-NPs layer with dopamine.
In the final step, the main sample was used as 1D-PC/ Chi-PANI-Au NPs in the main sensing setup. The Tamm plasmon can exited at the interface of the gold and 1D PC based on 28 alternating the SiO2 and TiO2 layers. The layers were well known that 1D-PC with cover layer like as Au ones, shows main mode in the middle of photonic band gap as Tamm plasmon mode without sensitivity to incidence polarizations. The experimental setup was adjusted onto 46-degree incidence angle and after verifying the main Tamm mode, this mode was used to sense the dopamine with four different concentrations (1, 3, 5 and 7 ppm) as F1 to F4 samples and at seven different times (26, 30, 33, 37, 42, 76 and 79 min) as t1 to t7.
The blue shift observed in the main mode of the photonic crystal for the concentration of F1 and over time in the Fig. 6. From a wavelength of 600 nm without the presence of dopamine, it shifted to 604 nm in 26 minutes and then reached a wavelength of 594 nm with a redshift after 42 minutes. This behavior is associated with redshift over time. This behavior is repeated at other concentrations, and at the maximum concentration of F4, it encounters more wavelength shifting.
Fig. 6. Reflection of the sensor in four different concentrations (a) F1 (1 ppm), (b) F2(3 ppm), (c) F3(5 ppm) and (d) F4 (7 ppm) and seven elapsed times.
The measurement is reliable in the short time and the response of sensor is fast. It can be explained by this fact that the main optical mode shifted and saturation state in the interaction of dopamine with gold NPs as it is confirmed beforehand by the observed shift in the functional group of C-O and N-H group shown in Fig. 7(b).
Repetition in the main mode shift after the elapsed time from the sample are also summarized in Fig. 7(a). As shown in this figure, for all four concentrations, in 42 min (t5) we reach to the maximum shift in the Tamm plasmon mode with the same trend and after that due to the uncoupling of C-O and N-H groups after time lapses it decreases. The gold nanoparticles contain the free electron and it is dispersed in the chitosan-PANI solution. Chitosan has an affinity to the transition of Au-NPs and PANI due to amino (-NH2) and hydroxy groups. The NH group of PANI is another candidate to cap the gold nanoparticles using the Van der Waals connection (Fig. 7(b)). Therefore, the gold nanoparticles increased the conductivity and affinity of the composite to connect with other molecules. Dopamine has two hydroxyls and one amino group that they can interact with gold nanoparticles and PANI. Therefore, dopamine attached to Chi-PANI-Au-NPs and surface adsorption occurred; therefore, this has affected the optical properties of Chi-PANI-Au-NPs. Due to the interaction of dopamine with the PANI-Au-NPs, the blue shift occurred and the blue shift was observed until the saturated in the first bind layer and after that, the red shift occurred. As mentioned above, the blue shift and red shift were observed due to binding the different concentrations of dopamine in the surface of the Chi-PANI-Au-NPs layer and the same trend was observed. So, it confirms the repeatability of the sensor’s response to different concentrations of dopamine and it authenticates the surface stability.
Fig. 7. a) Tamm plasmon mode shifting as a function of elapsed time from t1 to t7 for F1 (1 ppm), F2(3 ppm), F3 (5 ppm) and F4 (7 ppm), b) the molecular model for interaction of Dopamine with the Chi-PANI-Au-NPs composite.
The sensitivity of sensor is the variation of sensor output (shift in wavelength) with the variation of dopamine concentration as follows [49]:
Figures 8(a) and 8(b) show the variation of wavelength shift in the presence of Chi-PANI-Au-NPs sensing layer and PC without any sensing layer, respectively. The response Tamm plasmon sensor can be calculated from the slope of each line (Eq. (9)). Therefore, the response of sensor increased 3.158 times when the experiment was carried out with Chi-PANI-Au-NPs.
Fig. 8. The variation of wavelength with different concentration of dopamine a) without sensing layer (slope:16.96${\pm} 4.13415$) b) with sensing layer (slope:53.5647${\pm} 6.28$).
In this study, the Chi-PANI-Au-NPs was used to detect dopamine. Chitosan is a natural polymer and it is a good candidate to cap the nanoparticles also. Consequently, the chitosan has a matrix role to sustain the nanoparticles. Moreover, chitosan contains amino (-NH2) tail in the chain and it causes to increase in the cross-section of binding. The PANI is a polymer conductive and the main role was to capture the analyte, and PANI increased the cross-sectional area of the interaction of the sensing layer with dopamine via functional groups including NH + . Moreover, the Au-NPs increased the plasmonic and conductivity of PANI. The sensing layer (Chi-PANI-Au-NPs) was coated on the surface of the gold layer because the surface plasmon wave can generate at the interface of the gold thin layer dielectric layer. The system of the sensing layer was designed to improve the sensitivity and the cross-sectional area of the interaction of the sensing layer with dopamine. This is suggested to increase the stability, reliability for a long time, and sensitivity the matrix for sustaining the nanoparticles should be added to other polymers or chitosan should be modified with the crass linker. Another suggestion is that use silver nanoparticles instead of gold nanoparticles.
4. Conclusions
In summary, we designed and fabricated one dimensional photonic crystal with cover metallic layer as 1D-PC/Chi-PANI-Au NPs structure as new kind of Tamm plasmon based Dopamine sensor. After complete characterization of the main sensor head, we dropped four different concentrations of dopamine onto that and recorded the Tamm plasmon mode shifting. Our results show the maximum shift in the Tamm plasmon mode with the same trend for four different concentrations, afterward it decreases due to the uncoupling of C-O and N-H groups by elapsed time. Our results here provide strong basis for future Dopamine biosensors by means of photonic structures.
Acknowledgments
Author Contribution. Farnaz Amouyan measured, analyzed and wrote the main text of the manuscript, A. R. Sadrolhosseini and S. M. Hamidi supervised the work and checked all of the measurements and the writing process, M. Kazemzad fabricated the chitosan sample and M. Hamzezadeh helped in editing and analyzing the process.
Disclosures
The authors declare that they have no conflict of interest.
Data availability
All of data in this paper available by request.
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