We report a simple and compact modal interferometer for applications in refractometry. The device consists of a stub of large-mode-area photonic crystal fiber (PCF) spliced between standard single-mode fibers. In the splice regions the voids of the PCF are fully collapsed, thus allowing the coupling and recombination of PCF core and cladding modes. The device is highly stable over time, has low temperature sensitivity, and is suitable for measuring indices in the 1.330–1.440 range. The measure of the refractive index is carried out by monitoring the shift of the interference pattern.

Present study demonstrates the fiber-optic localized surface plasmon resonance (LSPR) based sensitive biosensor for detection of Shigella bacterial species. The proposed sensor is comprised of multi-core fiber (MCF) having seven cores arranged in a hexagonal shape and spliced with single-mode fiber (SMF) for efficient detection. An increase in evanescent waves (EWs) and coupling of modes between MCF cores was achieved by etching process in a controlled manner. The etching process also increases the refractive index sensitivity (RIS) of the proposed sensor. Further, coating with nanomaterials like gold nanoparticles (AuNPs) and molybdenum disulfide (MoS ₂ ) helps in the excitation of localized plasmons. Here, Shigella specific oligonucleotide probes are used as a recognition element. The results demonstrate that the proposed sensor can successfully and efficiently detect the Shigella bacterial species with high sensitivity. Shigella in the range of 10 - 100 CFU/mL (colony-forming unit/mL) can cause serious intestinal infection and therefore, its detection in this range is critical. The proposed sensor demonstrates a linearity range from 1 to 10 ⁹ CFU/mL with a detection time of 5 min and a limit of detection (LoD) of 1.56 CFU/mL. The proposed sensing methodology can be a potential alternative to the commercially existing ones in the near future.

A high-accuracy aluminum-based surface plasmon resonance (SPR) chalcogenide sensor is proposed for IR. The structure is based on widely used 2S2G chalcogenide glass with aluminum as the SPR active metal. The angular interrogation method has been used to study the performance of the sensor in terms of intrinsic sensitivity (IS) that includes the width and shifts of the SPR curve for a given refractive index of sensing layer. The IS of Al-based chalcogenide glass sensor is almost 400% more as compared with an Au-based one, which is the most widely used SPR active metal. The oxidation problem of an Al-based SPR sensor has been addressed.

In this work, a localized plasmon-based sensor is developed for para-cresol (p-cresol) - a water pollutant detection. A nonadiabatic $40~\mu \text{m}$ of tapered optical fiber (TOF) has been experimentally fabricated and computationally analyzed using beam propagation method. For optimization of sensor’s performance, two probes are proposed, where probe 1 is immobilized with gold nanoparticles (AuNPs) and probe 2 is immobilized with the AuNPs along with zinc oxide nanoparticles (ZnO-NPs). The synthesized metal nanomaterials were characterized by ultraviolet-visible spectrophotometer (UV–vis spectrophotometer) and transmission electron microscope (HR-TEM). The nanomaterials coating on the surface of the sensing probe were characterized by a scanning electron microscope (SEM). Thereafter, to increase the specificity of the sensor, the probes are functionalized with tyrosinase enzyme. Different solutions of p-cresol in the concentration range of $0~\mu \text{M}$ – $1000~\mu \text{M}$ are prepared in an artificial urine solution for sensing purposes. Different analytes such as uric acid, $\beta $ -cyclodextrin, L-alanine, and glycine are prepared for selectivity measurement. The linearity range, sensitivity, and limit of detection (LOD) of probe 1 are $0~\mu \text{M}$ – $700~\mu \text{M}$ , 7.2 nm/mM (accuracy 0.977), and $59.90~\mu \text{M}$ , respectively; and for probe 2 are $0~\mu \text{M}$ – $1000~\mu \text{M}$ , 5.6 nm/mM (accuracy 0.981), and $57.43~\mu \text{M}$ , respectively. Thus, the overall performance of probe 2 is quite better due to the inclusion of ZnO-NPs that increase the biocompatibility of sensor probe. The proposed sensor structure has potential applications in the food industry and clinical medicine.