No abstract

In this paper, we determine the optical refractive indices of different molarities of glucose using nano-laminated gold/chromium (Au-Cr) thin film via Kretschmann-based Surface Plasmon Resonance (K-SPR) sensing with angular interrogation. The nano-laminated Au-Cr K-SPR sensor detects the glucose presence in low-and high-concentration of 4-12 mmol/L and 55-277 mmol/L, respectively, under the exposure of 670 nm and 785 nm optical wavelengths. The experimental results showed that the minimum limit of detection (LOD) of Au-Cr K-SPR is 4 mmol/L and the glucose sensor sensitivities are in average of 3.41 o /M and 2.73 o /M at 670 nm and 785 nm optical wavelength, respectively. Stable sensitivity for each concentration also shown from the sensorgram results, indicates the stable performance of nanolaminated Au-Cr SPR sensor to detect glucose in the range from mmol/L up to dmol/L. Values of refractive indices for glucose molarities obtained are 1.33187 (4 mmol/L) and 1.3191 (4 mmol/L) at 670 and 785 nm wavelength, respectively. These RI values are beneficial for numerical simulation of glucose sensors using nano-laminated Au-Cr thin films which have been reported for the first time. The sensor can be eventually deployed in integrated photonic sensing devices comprising of multiple analyte detection for lab-on-chip (LoC) and point-of care (PoC) applications.

Kretschmann-based Surface Plasmon Resonance (SPR) optical sensor was applied to detect the presence of kidney wastes such as urea in solutions. To enhance the sensitivity of the SPR sensor, nanolaminated gold film (thickness of 50 nm) was used. In this work, the SPR response to urea in various concentrations were measured and investigated using optical wavelengths of 670 nm and 785 nm. The signals were compared between pure urea solution versus mixed solution in the presence of the 0.227 µmol urease enzyme. The proposed mixed solution is to eliminate doping and gel entrapment process for enzyme immobilization in conventional method. Angular interrogation technique was used to measure the sensor performance in urea detection using pure and mixed solutions with urea concentration of 0-800 mM. Upon exposure to mixed solution using 785 nm optical wavelength, the nanolaminated gold film exhibited higher SPR sensitivity as much as 7.8 M-1 than a pure urea solution (1.4 M-1). The coupling activity between urea and urease molecules in the mixed solution near the nanolaminated gold film surface lead to sensitivity enhancement. Angle shifting of mixed solution on 50 nm-thick nanolaminated gold film using 670 nm optical wavelength was greater by ~50% compared to 785 nm. Sensorgram data shows a steady and linear increment in SPR incident angle shifting when urea concentration increased. To the best of our knowledge, this is the first time that Kretschmann-based SPR has been used for urea sensing at 670 nm and 785 nm optical wavelengths.

In this paper, Taguchi experimental design technique was applied for optimization of chromium (Cr)/silver (Ag)/indium tin oxide (ITO) SPR sensor for operation in near infrared region. Four factors were considered which include wavelength, thickness of Cr, thickness of Ag, and thickness of ITO. Finite-difference-time-domain (FDTD) method was used in numerical analysis for minimum reflectance (R min) and full-width-at-half-maximum (FWHM) performance parameters. The results obtained from the Taguchi method shows that the optimized parameter for R min was 785 nm of wavelength, Cr (1 nm), Ag (40 nm) and ITO (20 nm), whereas the optimized parameter for FWHM was 785 of wavelength, Cr (0 nm), Ag (40 nm) and ITO (0 nm). In short, the optimum parameters for achieving the desired performance of sensor were successfully predicted using Taguchi optimization method.

The present paper analyses a surface plasmon resonance (SPR) biosensor based on graphene that leads to improvement on the efficiency of an urea biosensor due to high adsorption. Kretschmann configuration is well known as the most effectively used technique for plasmon excitation. In this work, we investigated the effect of MoS 2 with a fine layer of graphene deposited on a plasmonic material, gold (Au), into the configuration. Simulation is based on finite-difference time domain (FDTD) method for analysis. The performance of SPR biosensor can be monitored by analyzing the sensitivity and full width-at-half-maximum (FWHM) of the SPR spectrum. The measurements are observed at 670 and 785 nm for urea detection. The molarity and refractive index is varied from 1.335 to 1.342 for the sensing layer. The results showed that the percentage increase in sensitivity for the proposed biosensor Au/MoS 2 /graphene over conventional biosensor Au is 98% and 202% at 670 and 785 nm, respectively, which indicates that the proposed novel SPR biosensor is better suited for urea detection.