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Abstract
In this paper, we proposed and analyzed a simple circular slotted micro-channel photonic crystal fiber (MC-PCF) based surface plasmon resonance (SPR) sensor. Using finite element method (FEM) the numerical performances are investigated with an external sensing approach. Gold is a chemically stable material that is used in the purpose of plasmonic material at the thickness of 30nm. Simulation results show that the maximum wavelength sensitivity (WS) 25,000 nm/RIU having wavelength resolution (WR) of 4×10−6 RIU, maximum amplitude sensitivity (AS) is obtained about 1897 RIU-1 showing amplitude resolution (AR) of 6.25×10−6 RIU. In addition, figure of merit (FOM) is found about 277.77 RIU-1 for the analyte refractive index (RI) changes from 1.43-1.44 (RIU). The major nobility is that the proposed sensor shows a broad detection range from 1.33-1.47 RI with the wavelength range from 0.55 to 1.80 µm. Because of the promising sensitivity the proposed model can be applicable for biomolecules and biochemical (i.e., DNA, mRNA, sugar, proteins, carbohydrates, lipids and nucleic acids) sample detection and play the greatest role to detect antibody antigen interaction to find out genome sequences.
© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
In this present era of science and technology in the advancing world, very low cost and lightweight biosensor is one of the most appreciated topics. For the enormous application fields like biosensing, antigen antibody interaction, gas sensing, water testing, food quality measurements environment testing, biomedical applications, analyte detection etc. [1], the photonic crystal fiber based SPR biosensors are widely recommended. SPR biosensors detect biological samples by the mechanism of resonance for between metal surface free electrons and light beam evanescent electromagnetic wave from the core of the fiber. The term PCF refers to the circular optical fiber with air holes inside it. Those air holes act as lower density mediums for total internal reflection inside the fiber.
In very earlier, Kretchsmann configuration introduced as SPR sensor where the sensor had made using prism coupling [2] but this sensor could not last long due to its bulky size and very heavy unmovable mechanic parts. The configuration was eliminate by the fundamental idea of PCF, was firstly presented by Yeh et al. [3] in 1978 and implemented by Jorgenson in 1993, introducing optical fiber based SPR biosensor [4]. After various types of PCF like highly birefringence [5], ultra-flattened dispersion [6], double cladding [7] had been introduced. Because of its high sensitivity, smaller size, flexibility, stability, high detection range, this optical fiber based PCF-SPR sensor is being widely appreciated since then.
The sensing mechanism of the sensor is creating evanescent field of pole polarized light beams. When light is incident on the fiber core it creates evanescent field which produces pole polarized lights. This polarized light penetrates from the core and hit metal thin film surface surrounding the fiber and releases free electrons from the metal area. At a particular wavelength for identical refractive index (RI), the surface plasmon polariton (SPP) mode pole polarized light beams and the metal free electron frequencies matches with one another and creates resonance. At this resonance wavelength a huge energy is transferred from the fiber to the metal free electron. Observing this wavelength, we can detect unknown biological and chemical samples.
From the evaluation of sensors we know two kinds of sensing approach those are internal and external sensing approach. Firstly, internal sensing or nanowire-based [8] sensing the air hole is filled by the analyte and around the core the metal layer is placed [9]. Another sensing medium external sensing approach like slotted, micro channel and D shape sensors the plasmonic material is placed externally [10]. Because of internal sensing filled process is difficult and having more disadvantages so micro channel based slotted external sensing approach can be implemented easily to detect the bio-samples in practice.
The plasmonic material selection is one of the most important points to design a sensor. We introduced previously various plasmonic materials [11] like gold, silver, copper, titanium oxide, titanium nitride, aluminum, indium tin oxide and niobium. Gold is the most used plasmonic material for its chemical stability and highly shifted of resonance peak compare to others which is very important [10]. Silver is highly sensitive and gives sharper resonance peak but it is oxidized and becomes chemically unstable [12]. Fused silica uses as background material because of its low temperature sensitivity [13].
Recently various micro channel PCF based biosensor had introduced. Akter et al. proposed two open channel hexagonal lattice sensor that performed maximum wavelength sensitivity Sw is 5000 nm/RIU and amplitude sensitivity SA is 396 RIU-1 [12]. Z. Yang et al. proposed a SPR based on concave-shaped square channel PCF sensor using indium tin oxide (ITO) that showing the maximum Sw 10700 nm per RIU [14]. Emranul et al. proposed a modified D shape PCF sensor that showing maximum Sw is 20000 nm/RIU and SA is 1054 RIU-1 [15]. Next Hasan et al. proposed a slotted PCF based plasmonic sensor that showing maximum Sw is 22000nm/RIU and SA is 1782.56 RIU-1 [16]. M. H. K. Anik el al. designed a quadruple D-shaped open channel PCF using Silicon nitride (Si3N4) and titanium oxide (TiO2) with gold that showing Sw is 21000 nm/RIU and SA is 914 RIU-1 [17]. All those previously reported micro channel based sensor having some limitations like less sensitivity, not wide range and complex structure with lower fabrication tolerable performance.
In order to more better sensing performance with broad detection range than previously above mentioned sensor, here propose a sensor simple in structure, miniature size and highly sensitive as shows maximum wavelength sensitivity of 25,000 nm/RIU with a wavelength resolution of 4×10−6 RIU and amplitude sensitivity of 1897.27 RIU-1 with amplitude resolution 6.25×10−6 RIU. Gold is used as plasmonic material and numerical analysis has been performed using finite element method (FEM) with perfectly matched layer (PML) and scattering boundary condition with finer mesh analysis. All the structural parameter like gold layer thickness, air hole diameter, pitch parameter, detection range, diameter of PCF have optimized to get maximum wavelength sensitivity, amplitude sensitivity, wavelength resolution, amplitude resolution and FOM and also the simulation has been optimized by using world recognized FEM based simulation tools Comsol Multiphysics software.
For high detection range, high resolution, high sensitivity, polynomial curve fitting characteristics, figure of merit (FOM) and showing highly fabrication tolerable performance this sensor can be an appropriate candidate in bio-sensing approach.
2. Description of the structural design
The schematic structure, presentation of the proposed plasmonic sensor is delimited in Fig. 1(a) and the 3D view represent in Fig. 1(b). The main structure is designed by two air hole rings. The distance between center of the PCF and the center of the first ring air hole is denoted by pitch (Λ). The inner ring is organized by hexagonal shape air holes 1, 2, 3, 4, 5 and 6 with 60o angle gap from each other. The outer air hole ring is also pitch distance from the first ring which is circular shape air holes with 30o angle gap each other 7, 9, 10, 11, 13, 15, 16, 17 with missing air holes 8, 12, 14 and 18 for adding slot. The proposed structure first hexagonal shape ring smaller air hole diameter d = 0.57Λ and the second circular ring air hole diameter d1 = 0.78Λ.
Fig. 1. (a) Schematic 2D cross sectional view Λ = 3 µm, d = 0.57Λ, d1 = 0.78Λ and tg = 30 nm, (b) 3D view of the sensor structure and (c) Stacked method fabrication process structure of the sensor.
Finally the external coating gold (Au) layer as sensing layer which is circularly slotted micro channel based structure. The gold layer thickness is tg = 30nm and here Λ = 3 µm. The light is penetrate from the core and control the evanescent field pole polarized light beam by maintaining the gap between air holes position 1 to 2, 3 to 4, 4 to 5 and 1 to 6 to control the light and hit the metal-dielectric surface at slot position easily for creating SPR phenomenon. Figure 1(c) represents the stacked fabrication process structure of the sensor where the solid rod capillary is used for the design. The second ring air holes are represented by thin wall capillary and smaller air holes are represented by thick wall capillary.
As gold (Au) is a chemically stable material used for external sensing layer which thickness (tg) is variable and developed thin film by chemical vapor deposition (CVD) [18] method. The main background material is fused silica because of its temperature effect stability [13]. The RI of the silica material is calculated by the Sellmier equation and denoted by [19]:
To diminish the reflection of light the next layer is placed PML is 1.5 µm and also applied the sensing scattering boundary condition to imbibe the incoming evanescent field wave which is radiated from the PCF.
3. Simulation theory
The performance of the design PCF sensor is performed by master class numerical technique FEM based software COMSOL Multiphysics. During simulation the finer meshing elements are used and found that the number of total elements 19,424, number of vertex elements 100 numbers of boundary elements 1,562 and the quality of the element is 0.7722. The performance analysis of the proposed sensor by calculating the loss of the sensor by the following formula [22]:
where, Im(neff) refers to the core mode effective mode index imaginary part, ${k_0} = \frac{{2\pi }}{\lambda }$ is the propagation constant and λ is the operating wavelength [23].The performance analysis of the proposed sensor main subject is the wavelength sensitivity and amplitude sensitivity. Both of them are calculated based on the interrogation method. The wavelength sensitivity of the proposed plasmonic sensor calculated from the following formula [24].
where Δλpeak is the wavelength difference of the two adjacent analytes resonance peak and Δn is the RI difference of the two adjacent analytes. The amplitude sensitivity of the proposed plasmonic sensor can be calculated from the following formula [25]:To identify the sensing ability of the sensor resolution is the very important parameter. The formula for the calculation of sensor resolution [26]:
where Δna is the two adjacent refractive index changes, Δλpeak is the two adjacent resonance peak wavelength difference, Δλmin is the minimum sensing resolution. Another important performance parameter is FOM which is calculated by the equation [27]: where FWHM means the full width at half maximum. More FOM exhibits a higher sensing performance. From the equation we observe that higher FOM can be obtained by increasing sensitivity and decreasing FWHM.The plasmonic material constants value can be expressed by Drude-Lorentz model [28]. The dielectric function equation is given below:
The free electron effects inner band part $\varepsilon _r^f(\mathrm{\omega } )$ of the dielectric function is described by Drude model [29]:
The inter band part of the dielectric function $\varepsilon _r^b(\mathrm{\omega } )$ is described by Lorentz model [30]:
Here ${\mathrm{\omega }^p}$ is plasma frequency, K is the number of oscillators with frequency ${\mathrm{\omega }_j}$, strength ${f_j}$, lifetime ${{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 \Gamma }} \right.}\!\lower0.7ex\hbox{$\Gamma $}}_j}$ and $\Omega {\; _p} = \sqrt {{f_{o\; }}} {\mathrm{\omega }^p}$.
In this sensor design results analysis, the noble materials are gold (Au), Silver (Ag) and copper (Cu) impact on sensor performance. The values of the plasma frequencies are 9.03ev, 9.01ev and 10.83ev for Au, Ag and Cu respectively [31]. The values of Drude-Lorents model parameters are received from Ref. [31].
4. Simulation and results analysis
4.1 Phase matching and surface plasmon wave generating
The main working phenomenon of this biosensor is to sensing biomolecules and biochemical analytes by their refractive index detecting. Generally, the biological sample refractive index is in the range of 1.33-1.48 [32]. The main working principle of the SPR sensor is based on the guided evanescent field [33]. By properly designing the geometry of core and cladding the guided evanescent mode hit the metallic surface and stimulates free electrons from the metallic surface. When the wavelength or frequency of the core guided fields is same to the wavelength or frequency of the metal surface then a surface plasmon wave (SPW) is generated. Those SPWs are sensitive to the adjacent layer refractive index. So that by changing the analyte that means changes RI the SPWs is changes to another wavelength. For a particular analyte the SPWs generated at particular wavelength.
This is denoted by phase matching properties which represented in Fig. 2(d). Where the fundamental core guided mode and the SPP mode are matched for particular analyte at 1.45. From the figure we found that the real part of core mode and the SPP mode are intersect at the point wavelength 1.06µm. This wavelength is called phase matching wavelength and at this wavelength sharp resonance apex is observed. At the resonance wavelength maximum energy transfers from the core mode to the plasmonic mode. Figures 2 (a)-(c) shows the EM field of the x-polarized core mode, y-polarized core mode and the SPP mode.
Fig. 2. EM field distribution of fundamental (a) x-polarized core mode, (b) y-polarized core mode, (c) y-polarized SPP mode and (d) dispersion phase matching relation between the fundamental core mode and SPP mode at na = 1.45 and tg = 30 nm.
The performance of the sensor is investigated in terms of amplitude sensitivity, wavelength sensitivity, sensor resolution, resonance wavelength polynomial curve fitting characteristics, FOM fabrication tolerance performance and effect of plasmonic material change.
4.2 Analyte variation and sensitivity
In sensor performance calculation, confinement loss plays essential role because PCF biosensor works based on lossy behavior and it is obtained by using the Eq. (3). In Fig. 3(a) we plot the loss with respect to wavelength and we found that with the analyte variation the resonance loss peak shifted to different wavelength.
Fig. 3. (a) Analyte RI changing loss characteristic curve from 1.33 to 1.47 and (b) Amplitude Sensitivity curve with Λ = 3μm, d = 0.57 Λ, d1 = 0.78 Λ, and tg = 30 nm.
We observed that rising RI from 1.33-1.47 with step size increasing 0.01 the loss depth also increasing drastically because of the lower contrast of the core-clad refractive index as the effective mode index of core and cladding is reducing. The fused silica RI is approximately 1.44 so as when the analyte RI near to the silica RI the loss is increasing because of strongly coupling. So that this indicates the red shift as the individual RI loss peak, the phase matching point shifted to greater wavelengths.
Here, we plot only the y-polarized core mode and maximum loss depth is found 16.4656 dB/cm at analyte RI 1.47 and wavelength at 1.58μm. Greater loss depth leads to more guided mode penetrate to the cladding region so that the interaction with the analytes increases. By using wavelength interrogation method the wavelength sensitivity is found by using Eq. (4):
Therefore, the RI of analyte changes from 1.33 to 1.34, 1.34 to 1.35, 1.35 to 1.36, 1.36 to 1.37, 1.37 to 1.38, 1.38 to 1.39, 1.39 to 1.40, 1.40 to 1.41, 1.41 to 1.42, 1.42 to 1.43, 1.43 to 1.44, 1.44 to 1.45, 1.45 to 1.46 and 1.46 to 1.47. The wavelength sensitivities are calculated to 2000nm/RIU, 1000 nm/RIU, 1000 nm/RIU, 2000nm/RIU, 3000 nm/RIU, 2000nm/RIU, 4000 nm/RIU, 5000 nm/RIU, 7000 nm/RIU, 9000 nm/RIU, 13000 nm/RIU, 25000 nm/RIU, 15000 nm/RIU and 13000 nm/RIU respectively.
By using Eq. (6) to measure performance ability the maximum sensor wavelength resolution is found 4×10−6 RIU. The designed sensor can detect order of 10−6 at the analyte RIs variation.
By using Eq. (5) we calculate amplitude sensitivity and in Fig. 3(b) we plot the amplitude sensitivity with respect to wavelength with the analyte RI variation from 1.37 to 1.45. From the figure it is evident that the amplitude sensitivity increasing monotonically but at 1.45 RI the amplitude sensitivity is increasing drastically and maximum 1897.27 RIU-1. The maximum amplitude sensitivity is found at wavelength 1.46μm. Again, according to Eq. (6) the maximum amplitude resolution is found 6.25×10−6 RIU. For those reason our sensor can be sensed order of 10−6 with changing smallest RI change.
4.3 Performance analysis of gold layer thickness variation
The performances of the sensor are greatly affected the variation of the gold layer thickness. According to Fig. 4 we observed that the loss characteristics curve peak is decreases as increases of gold layer thickness because when the gold layer is thin then the light is strongly coupling at the SPP mode and core mode. The resonance wavelength is shifted slightly with the variation of gold layer thickness and for RI change the red shift characteristics is occurred. For the analyte RI at 1.45 the maximum loss depth are found 9.48 dB/cm, 9.17 dB/cm, 7.30dB/cm and 5.25dB/cm at the resonance wavelength of 1.32μm 1.3μm, 1.28μm and 1.27μm with the gold layer thickness of 25nm, 30nm, 40nm and 50nm respectively. Again, for the analyte RI at 1.46 the maximum loss depth are found 35.24dB/cm, 15.88dB/cm, 11.90dB/cm and 7.53dB/cm at the resonance wavelength of 1.47μm, 1.45μm, 1.41μm and 1.40μm with the gold layer thickness of 25nm, 30nm, 40nm and 50nm respectively.
Fig. 4. Gold layer thicknesses variation and loss for 1.45 and 1.46 and thickness of tg = 25 nm, 30 nm, 40 nm, and 50 nm.
Also from the Fig. 5 for the analyte RI at 1.45 the maximum amplitude sensitivity are found 1468.78 RIU-1, 1897.2 RIU-1, 852.11 RIU-1 and 290.98 RIU-1 with the gold layer thickness 25nm, 30 nm, 40 nm and 50 nm respectively. From Fig. 5 we noticed that with the rising the gold layer thickness the loss depth and amplitude sensitivity reducing but for 25nm the amplitude sensitivity value is lower. Therefore, the optimum gold layer thickness is selected as 30 nm; see Table 1.
Fig. 5. Amplitude sensitivity with thickness variation tg = 25 nm, 30 nm, 40 nm and 50 nm at na=1.45.
4.4 Performance analysis of pitch variation on the sensor
Pitch (Λ) means the center to center distance of two air holes. It is found that the variation of Λ greatly influence on sensing performance. Because when the pitch value increases then the distance between core and cladding also increases so that the loss depth decreases because more light passing through the core mode. From Fig. 6(a) we see that the pitch value increases from 2 to 3μm the loss depth is decreases 16.82 dB/cm to 6.95 dB/cm at analyte na=1.44μm and also found that red shifted phenomenon is observed as the resonance wavelength is shifted 0.90 to 1.05μm. Same types of results are found as the Λ increases from 3 to 3.5μm.
Fig. 6. (a) Loss Spectrum with the pitch (Λ) variation at 2μm, 3μm and 3.5μm for analyte 1.44 and 1.45, (b) Analyte variation (1.35 to 1.46) for Λ=3.5μm and (c) Amplitude Sensitivity curve with the pitch (Λ) variations at 2μm, 3μm and 3.5μm and the other parameter at tg = 30 nm, d = 0.57 Λ, d1 = 0.78 Λ.
All the results from Fig. 6(a) is put on the Table 2. From the Table 2 we see that the highest WS is found as 31000 nm/RIU for Λ=3.5 μm. The analyte variation RI range from 1.35 to 1.46 put on Fig. 6(b) but from Fig. 3(a) for Λ=3μm the analyte RI variation is found 1.33 to 1.47 that better sensing range.
Table 1. Optimization of gold layer thickness
Table 2. Results analysis by virtue of pitch changing on Loss peak, Resonance Wavelength (RW), Wavelength Sensitivity (WS) and Amplitude Sensitivity with constant tg = 30 nm, d = 0.57 Λ, d1 = 0.78 Λ.
We also found from the Fig. 6(c) that as the Λ value increases the maximum AS is decreases. We see that for the analyte 1.45 when the Λ value at 2μm, 3μm and 3.5μm the maximum AS is found 2186.90 RIU-1, 1897.27 RIU-1and 1217.28 RIU-1, respectively. So that we found at 3.5μm the AS is less only 1217.28 RIU-1.
On the other hand at Λ=2μm the AS value is more 2186.90 RIU-1 but WS less only16000 nm/RIU. To sum up we optimize the Λ value at 3μm with AS 1897.27 RIU-1 and WS 25000 nm/RIU also better sensing range 1.33 to 1.47 RIU.
4.5 Resonance wavelength CL intensity profile and polynomial curve fitting characteristics with the function of RI
The sensing performance is highly depended on the adding ability between the core guided mode and the plasmonic mode. Figure 7(a) shows the confinement loss (CL) intensity profile in normalized form. We see that with the increasing refractive index (RI) the coupling efficiency is also increasing. At RI 1.33 the intensity is minimum and RI 1.47 the intensity is maximum as the loss increasing with increasing of RI of the resonance wavelength.
Fig. 7. (a) Intensity loss profile normalized form and, (b) Polynomial curve fitting characteristics of RW with respect to RI with na (1.33 to 1.46), Λ = 3μm, tg = 30 nm, d = 0.57 Λ, and d1 = 0.78 Λ.
Curve fitting characteristics of the Resonance Wavelength (RW) is very important for the analysis of the sensor performance. It is needed for optimizing the sensor structure. In Fig. 7(b) we plot RW with respect to RI (1.33 to 1.47 at the y polarized core mode) and we see that polynomial curve fitting characteristics found where dot sign represents the resonance wavelength and solid lines represents the polynomial curve fitting. Here, we also found that a polynomial equation is
Given equation is a fourth order polynomial equation where x is the RI value and y is the RW value and also the most important value highly adjusted R2=0.9981 which is close to unity value. So that the proposed circular slotted Micro Channel based plasmonic biosensor practically implement efficiently. The detail values of the Fig. 7 are inserted on Table 3.
Table 3. Performance analysis details results-
4.6 Performance analysis on figure of merit
For the performance analysis of better sensor measuring FOM is must. The higher value of FOM defines the master class performance of the sensor. FOM is called the signal to noise ratio (SNR) but for the performance analysis of the sensor sensitivity is the major topic. From the Eq. (7) we calculate the FOM value where define that FOM is the ratio of the sensitivity and the FWHM (Full width at half maximum). So that higher FOM indicates better performance that means more sensitivity value. According to Eq. (7) we plot FOM in Fig. 8. We take FOM with respect to RI (from 1.33 to 1.44) and it is visible that with the increasing analyte refractive index (na) the sensitivity is increasing and the FWHM reduce as the narrow resonance peak is observed according to the Fig. 3(a) and the description of section 4.2. For RI 1.44 the WS value is 25000nm/RIU and FWHM value is 90nm therefore, the maximum FOM is found 277.77 RIU-1 at RI na = 1.44. The detail calculation of FOM value of Fig. 8 is inserted on Table 3.
4.7 Fabrication tolerance performance analysis
Fabrication tolerance test is very important performance analysis for fabrication. During fabricate it is very difficult to fabricate accurately according to desire parameter. So that performance of fluctuation how much is observed by fabrication tolerance test. In this sensor design here test the fabrication tolerance two major ways such as thickness of gold layer tolerance test and pitch tolerance test.
4.7.1 Gold layer thickness fabrication tolerance test
Here test the thickness variation of gold layer to ±5% and ±10% concerning optimized thickness value. The optimized thickness value is 30 nm. The fabrication tolerance performance of thickness variation has showed in Fig. 9. From the Fig. 9(a) we observe that the loss characteristic curve during rising almost same for ±5% and ±10% both parameters. But during peak and decaying loss characteristic curve is slightly shifted. And also from Fig. 9(b) the amplitude sensitivity curve of the fabrication tolerance test for RI 1.45 with ±5% and ±10% is slightly shifted the amplitude sensitivity value. However we say that the gold layer thickness fabrication test shows highly tolerable performance for ±5% and ±10% thickness variation concerning optimized value.
Fig. 9. (a) Loss characteristic curve of fabrication tolerance test, (b) Amplitude sensitivity curve of fabrication tolerance test at ±5% and ±10% of gold layer thickness 30 nm.
4.7.2 Fabrication tolerance test of pitch value
Figure 10(a) shows the fabrication tolerance test loss characteristic curve of pitch value at ± 2.5% and ±5% concerning optimize pitch value at 3μm and Fig. 10(b) shows the fabrication tolerance test amplitude sensitivity of pitch value at ± 2.5% and ±5% concerning optimize pitch value at 3μm. From the both figure we observe that due to pitch value change the loss curve and amplitude sensitivity curve are almost same not major impact on performance. So that proposed sensor can be showed the highly tolerable performance for both cases.
Fig. 10. (a) Loss characteristic curve of fabrication tolerance test, (b) Amplitude sensitivity curve of fabrication tolerance test at ±2.5% and ±5% of pitch value 3μm.
4.8 Effect of plasmonic material change on sensing performance
In this sensor design results analysis we observe the noble materials are gold (Au), Silver (Ag) and copper (Cu) impact on sensor performance. From the Fig. 11 we observe that the loss peak shifted equal for the three materials so that the wavelength sensitivity is almost same to 25000nm/RIU. Gold is a stable material with less sensitive to temperature and humid issues than silver than copper (Cu) so that here selected gold the best plasmonic material for the sensor design. The details results of Fig. 11 are put on the Table 4.
Table 4. Selection of suitable plasmonic material for the sensor-
4.9 Practically experimental set up process of the proposed sensor
After completed fabrication process of the proposed sensor next target will be the practically implementation. Figure 12 shows the practically implementation process of the proposed sensor. The sensor is connected with a single mode fiber (SMF). The sensing sample analyte is passed through by a pump from input to output analyte layer of the sensor. So that the inter activity between the sensing layer and analyte observed by the optical spectral analyzer (OSA) and the results display in the computer. In display results if the sensing response shift to the longer wavelength with concerning reference is called red shift on the other hand shorter wavelength is called blue shift. From this technique we can be detected the unknown analyte very easily and so fast.
To prove performance ability of our designed sensor all the performance parameter calculated results compare with the existing sensor put on the Table 5. From the table it is evident that our proposed sensor shows better results with higher sensitivity, more sensing capacity and the number of more detection range with compare the existing sensor.
Table 5. Performance comparison with the previously designed existing sensors-
5. Conclusion
A highly sensitive circular slotted micro channel PCF based SPR biosensor is proposed here where chemically stable material gold is deposited as a plasmonic material to deploy external sensing approach. Sensing performances are analyzed using FEM method and all the structural parameter are optimized and the maximum AS is 1897.27 RIU-1 with the maximum WS 25000 nm/RIU at the detection range 1.33 to 1.47 (RIU). Also having highly detection ability of 10−6 order as the maximum wavelength resolution and amplitude resolution are 4×10−6 RIU and 6.25×10−6 RIU respectively. As the sensor is highly sensitive the maximum FOM is found that 277.77 RIU-1. Finally we can summarize that our proposed sensor micro- channel structure the gold layer is placed the micro structured area not all the circular layer so that the sensor low cost and highly sensitive to sense biochemical and biological sample.
Acknowledgments
Alhamdulillah, by the grace of Almighty Allah (SWT), We have done a research paper. we would like to gratefully and sincerely thank Md. Saiful Islam and Rifat Ahmmed, Rajshahi University of Engineering and Technology for their constant inspiration, patience, necessary guidance, continuous help, suggestions, technical support and most importantly, their friendly dealing during this research work. They encouraged me not only perform the research work but also to grow as an independent thinker.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
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