Satyendra Kumar Mishra

An SPR-based sensor with an extremely large dynamic range of refractive index measurements in the visible region

A promising GaP prism-based surface plasmon resonance sensor in the Kretschmann configuration with an extremely large dynamic range of refractive index detection is proposed. The prism base is coated with a gold layer and then a thin layer of silicon. The sensor is studied theoretically in terms of sensitivity and detection accuracy. The proposed sensor shows the potential of sensing media with a refractive index varying from gaseous to very dense liquid with appreciably high sensitivity.

Wide-Range pH Sensor Based on a Smart- Hydrogel-Coated Long-Period Fiber Grating

We report a fiber-optic sensor for pH measurement, which is a long-period fiber grating (LPFG) coated with smart hydrogel. When the pH of a solution that surrounds the hydrogel coating changes, the volume of the coating and hence its refractive index are changed, which results in a shift in the resonance wavelength of the LPFG. Our experimental sensor shows a sensitivity of ~0.66 nm/pH over the pH range from 2 to 12 and a response time of less than 2 s. The effects of the refractive index of the surrounding solution and temperature variations on the sensor are also measured.

Surface-Plasmon-Resonance Refractive-Index Sensor With Cu-Coated Polymer Waveguide

We propose a refractive-index sensor based on the principle of surface plasmon resonance (SPR) in a polymer channel waveguide coated with a copper (Cu) film. Our fabricated device using a 40-nm Cu film covered with a 10-nm silicon-dioxide protecting layer offers a maximum refractive-index sensitivity of ~45 μm/RIU for the refractive-index range from 1.5375 to 1.5515, which is far more sensitive than the existing fiber/waveguide-based SPR sensors. The experimental results agree well with the theoretical analysis. We also present a sensor design with a record-high sensitivity of ~250 μm/RIU for aqueous solutions by using low-index polymer materials. The proposed sensor structure could be developed for a wide range of biomedical applications.

MgF2 prism/rhodium/graphene: efficient refractive index sensing structure in optical domain

A theoretical study of a noble surface plasmon resonance (SPR) based sensing probe has been carried out. The sensing probe consists of a magnesium fluoride (MgF2) prism with its base coated with rarely used noble metal rhodium (Rh) and a bio-compatible layer of graphene. The refractive indices (RIs) of the sensing medium vary from 1.33 to 1.36 refractive index unit (RIU). The thickness of Rh and the number of graphene layers have been optimized for maximum sensitivity in a constraint set by the detection accuracy (DA). For the operating wavelength of 632 nm, the optimized sensing probe Rh (12 nm)/graphene (single layer) demonstrates sensitivity of ~259 degree/RIU with corresponding DA of ~0.32 degree-1 while for 532 nm of excitation, the optimized sensing probe Rh (12 nm)/graphene (three layer) exhibits sensitivity of ~240 degree/RIU and DA of ~0.27 degree-1.

Nano-functionalized long-period fiber grating probe for disease-specific protein detection

Optical biosensors have great significance for rapid and sensitive detection and monitoring of biomolecular interactions. Here, recent advancement in the nano-functionalized long-period fiber grating (LPFG) is used to develop a cost-effective approach for label-free and real-time detection of the carbonic anhydrase-IX (CA9) monoclonal antibody, a diagnostic biomarker in hypoxia condition cultured carcinoma cells.

Hydrogel-coated long-period fiber grating pH sensor

We report a long-period fiber grating coated with a specially synthesized hydrogel for the measurement of pH changes in an aqueous solution. The coated grating operates sensitively for the pH ranges 2-5 and 8-12.

Sensing of m-cresol with a long-period fiber grating coated with enzyme-entrapped gel

We present a long-period fiber grating coated with a specially synthesized enzyme-entrapped gel for the sensing of m-cresol. The sensor operates for an m-cresol concentration varying from 0 to 800 µM.

Surface Plasmon Resonance Sensor Based on a Polymer Waveguide with a Copper Thin-Film Overlay

We investigate theoretically and experimentally a refractive-index sensor based on surface plasmon resonance with a copper thin-film overlay deposited on a polymer waveguide. The sensor shows a very high sensitivity of about 37 μm/RIU.