One of the fundamental challenges of working with surface plasmon resonance (SPR) biosensors is their inherent lack of specificity. Being very sensitive to minute refractive index (RI) changes in their surrounding medium, SPR biosensors are highly susceptible to variations in pH, temperature, and buffer composition. Therefore, it is often necessary to include an additional validation step downstream to SPR biosensing, particularly for clinical analysis. In this proof-of-study work, we have tried to evaluate the utility of surface-enhanced Raman scattering (SERS) tags as secondary labels for validating SPR biosensor response. Accordingly, a Fibre-optic SPR (FO-SPR) biosensor set-up was fabricated by immobilizing anti-BSA antibodies on the sensor platform for capturing and sensing biotinylated-BSA as a model analyte. Subsequently, the bound analyte and the concomitant shift in SPR response were validated by employing streptavidin-functionalized SERS tags. Intriguingly, apart from validation of the SPR response, the SERS tags also significantly improved the sensitivity of the SPR response and provided semi-quantitative information on the bound analyte. Although utilizing SERS tags undermines the label-free tag of SPR biosensors, the huge improvement in sensitivity and specificity of the sensor makes it suitable for clinical analysis. Furthermore, SERS measurements with a portable Raman spectrometer utilized in this study further highlight the potential of this approach for achieving point-of-care (POC) sensing.

The Jackiw–Rebbi model is a relativistic quantum model credited with the theoretical predictions of zero-energy bound states and charge fractionalization prior to the discovery of topological insulators and the fractional quantum Hall effect. In this work, we demonstrate a photonic equivalent of the Jackiw–Rebbi model by resorting to photonic crystal band structure engineering. Specifically, our photonic realization employs two spatial inversion symmetric binary photonic crystals exhibiting complementary signs of differential effective mass parameter (δm) for their second bandgaps. Their concatenation manifests a step discontinuity in the spatial profile of the effective mass parameter, forming a domain wall at the photonic crystal interface. Upon analyzing the reflectance spectra of the concatenated photonic crystal structure, we find a midgap surface state localized at this domain wall. Furthermore, much in agreement with the Jackiw–Rebbi zero-energy solution, the materialized photonic surface state also exhibits a zero-energy character in a differential energy space corresponding to the δm parameter, which has been quantified experimentally. Crucially, the conceived zero-energy mode amounts to the observation of a peculiar surface state with polarization-indiscriminate dispersion that can help realize all-angle polarization neutral optics.

Ascertainment of photonic stopband absolute topological character requires information regarding the Bloch eigenfunction spatial distribution. Consequently, the experimental investigations predominantly restrict themselves to the bulk‐boundary correspondence principle and the ensuing emergence of topological surface state. Although capable of establishing the equivalence/inequivalence of bandgaps, the determination of their absolute topological identity remains out of its purview. The alternate method of reflection phase‐based identification also provides only contentious improvements owing to the measurement complexities pertaining to the interferometric setups. To circumvent these limitations, the Kramers–Kronig amplitude‐phase causality considerations are resorted to and an experimentally conducive method is proposed for bandgap topological character determination directly from the parametric reflectance measurements. Particularly, it is demonstrated that in case of 1D photonic crystals, polarization‐resolved dispersion measurements suffice in qualitatively determining bandgaps’ absolute topological identities. By invoking the translational invariance of the investigated samples, a parameter “differential effective mass” is also defined, that encapsulates bandgaps’ topological identities and engenders an experimentally discernible bandgap classifier.

We developed a "metal-molecule-metal nanoparticle" ( MMNP) configuration on a fiber-optic SPR sensor system in the present work. For this, a gold-coated optical fiber (with an exposed core in the central portion) was used, and this goldcoated surface was first functionalized with the self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) molecules. The 4-ATP SAMs were functionalized with biotin molecules through EDC/NHS coupling agents. Separately, citrate-capped gold nanoparticles (similar to 20 nm) were synthesized and subsequently functionalized with streptavidin protein, which exhibits exceptional binding affinity towards biotin molecules. To establish the MMNP configuration, streptavidin-functionalized gold nanoparticles were flown over a biotin-functionalized SPR sensor surface. The Raman signal of 4-ATP molecules in the SPR sensor region was collected before and after interaction with streptavidinfunctionalized gold nanoparticles. The Raman signals of the sensor region exhibited huge enhancement after interaction with gold nanoparticles, confirming the creation of the hypothesized MMNP configuration on successful biomolecular interaction between streptavidin-functionalized gold nanoparticles and biotin molecules on the SPR sensor surface. Concomitant with the Raman signal enhancement, a marked shift (similar to 3-fold) in the SPR peak is also observed when interacting with the gold nanoparticles.

Using a solid state reaction mechanism, ZnS:Mn:Eu, a mechano-luminescence material, is synthesised and characterised with X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, Photoluminescence (PL), and Mechano-luminescence (ML) analytical techniques. Using the blending method, a composite of ZnS: Mn:Eu and piezotronic Polyvinylidene fluoride (PVDF) is then created. During processing of the ZnS:Mn:Eu composition with PVDF, the weight ratio of PVDF is varied from 5% to 50%. The polymeric composite is then cast into thin films and capped with a water-resistant transparent Polydimethylsiloxane (PDMS) polymer film for protection. For mechanoluminescence research, the author also uses a state-of-the-art, customised anodized aluminium (Al) cup-shaped fibre optic pigtailed assembly. This assembly contains the manufactured ML thin film and functions as an ML sensor. The obtained result demonstrates that 15 wt% of PVDF produces more intense ML emission than the other weight ratios. This research can serve as a stepping stone in the development of energy -efficient ML-based sensors for future advanced applications such as intelligent optical sensors, real-time pressure mapping systems, and information encryption techniques.

This work comprehensively investigates possibilities of surface states realization in one-dimensional photonic systems that are terminated with ������-negative and ii-negative bandgap materials. We begin by first fathoming the topological properties of photonic band structure and notice that its bulk properties completely characterize the surface phenomena in all the foreseeable cases. This approach is inspired from topologically non-trivial behavior in low-dimensional condensed matter systems and the ensuing emergence of topologically protected edge states in such systems. Specifically, we will be following the setup of Su-Schrieffer-Heeger model and emulate the topological phenomena in one-dimensional photonic systems with a substantial advantage of relatively less demanding fabrication. More importantly, being distributed systems, the photonic crystal realizations in question further enrich the available parameter space and provide application avenues for topological phenomena. For example, unlike the atomic chains, in the case of photonic crystals, we can achieve the band inversion and topological phase transition without altering the arrangement of constituents. Our investigations primarily focus on exploiting this very aspect of higher-order photonic bandgaps and in this process, we experimentally demonstrate that the bulk-band geometric phases offer a deterministic yet customizable route for surface state engineering.

Herein, we report a simple, low-cost substrate for surface-enhanced Raman spectroscopy (SERS). We utilized TLC plates as SERS substrates that has an edge over other paper-based substrates. Rhodamine 6G is used as Raman probe molecule to evaluate the performance of substrate.

This study is focused on the fabrication and testing of piezo-luminescent ZnS:Mn/PU composite thin film coated disc for self-powdered optical devices based on the mechano-luminescence phenomenon.

Topological band theory provides a framework to establish the equivalence/inequivalence of bandgaps in photonic topological insulators. However, experimental discernment of bandgap topological characteristics encounters inherent measurement complexities, particularly beyond the terahertz frequencies. To surmount this difficulty, we resort to the prolific optical technique of spectroscopic ellipsometry and carry out detailed experimental examination of attributes of one-dimensional photonic crystal stopbands and, in consequence, identify an appropriate classifier of the implicit topological characteristics. It is found that governed by the bulk topology, the band edge locations in the dispersion diagram provide a conditional site for the appearance of zeros of a complex reflection ratio. This leads to a selective appearance of topologically robust phase singularities with integer (unity positive) topological charge. We demonstrate that the presence of these phase singularities on either the blue or the red band edges of the stopbands provides us with an experimental marker of their distinctive topological characteristics.

Mechano-luminescence (ML) phenomenon is a non-destructive light generation mechanism with the effect of applied dynamic pressure on the materials. Here in present work, Mechano-luminescence response of Manganese (Mn) doped ZnS microcrystal is measured as a function of applied pressure and Mn concentration. First, ZnS is doped with three concentrations of Mn (0.5 M%, 1.0 M% and 1.5 M%) using solid state reaction mechanism at 1000 degrees C in an inert Argon atmosphere. The obtained material is characterized with Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Photo-luminescence (PL) techniques. The core mechano-luminescence (ML) signature of all samples is obtained using a custom designed dynamic vertical pressure impact setup. The pressure range for the experiments is kept from 10 to 400 bar with a gap of 50 bar for each measurement. It has been found that for ZnS:Mn with 1 M% doping concentration shows the highest ML emission intensity in comparison to 0.5 M% and 1.5 M%. It is also observed that ML intensity increases linearly with applied pressure for all three doping concentrations. Author has also discussed the decay time of signal with applied pressure. Results obtained show decrease in decay time for each drop height for all the samples. The current study clearly shows that ZnS:Mn has the ability to be used as an optical pressure sensor matrix material for impact sensor application.

We have designed, investigated, and experimentally realized a topological surface state (TSS) localized at the interface of two stratified photonic media. The manifested state is protected by the spatial inversion symmetry of the constituents, which permits the assignment of quantized topological invariants to them. The genesis of the surface state can be traced to the characteristic difference in the bulk topological behavior of the underlying stopbands. Specifically, in the present realization of TSS, we have resorted to a concatenation of topologically inequivalent first and second-order stopbands of two planar photonic crystals and established the disparity in their stopband characteristics.

The performance of a multimode fiber optic surface plasmon resonance (FO-SPR) sensor has been studied, both theoretically and experimentally, as a function of three crucial parameters - metal layer thickness, tapering ratio (TR) and fiber surface roughness. A combined approach is adopted to investigate the effect of these three parameters on FO-SPR sensor performance instead of considering them individually. Intriguingly, the three parameters are found to be highly correlated and their combined effect significantly influences the FO-SPR sensitivity. It is observed that optimum gold thickness to attain maximal sensitivity varies for different tapering ratios. Moreover, increasing the tapering ratio does not always increase the sensitivity as claimed in previous studies, but instead depends on the fiber surface roughness generated during chemical etching. The optimized FO-SPR sensor exhibits a high sensitivity of 4714 nm RIU-1 with standard glycerol solution in the refractive index (RI) range of 1.372-1.388. Furthermore, the optimized FO-SPR sensor has been employed for label-free detection of bovine serum albumin (BSA) and parathion pesticide. The system is able to detect BSA concentration as low as 1.5 pM and the parathion pesticide is detected at 0.1 ppb levels.

Selective and rapid detection of nitroexplosives is one of the vital issues for human security as well as environmental safety. Fluorescence based detection methods have gained attention due to its high sensitivity, simplicity, short response time and ability to detect analytes both in solid and liquid phase. Herein, we report a fluorescent europium based Metal Organic Framework (MOF) for selective sensing of trace amounts of nitroaromatic compounds. Detection is done on basis of fluorescence quenching effect of different concentrations of nitrobenzene solutions. The experimental results showed that Eu-MOF extremely sensitive towards trace amount of nitrobenzene and show high selectivity among other non-nitroaromatic compounds as well.

The molybdenum disulfide (MoS2) nanosheets functionalized fiber optic surface plasmon resonance (SPR) immunosensor has been reported for the sensitive detection of Escherichia coil (E. coli). The MoS2 nanosheets were prepared by chemical exfoliation method. The synthesised nanostructures were characterized for their structural, morphological and optical properties. The E. coli monoclonal antibodies were successfully immobilized on the MoS2 functionalized sensing platform via hydrophobic interactions. An alternative method simplifying the antibodies immobilization process by functionalization of 2D nanomaterial (MoS2 nanosheets) for rapid (similar to 15 mins) bacterial quantification is presented in this study. The immunosensor uses wavelength interrogation method and a strong linear relationship (R-2 = 0.994) was observed between spectral response of immunosensor and different concentration of E. coli. The nonspecificity and cross-reactivity studies of the developed immunosensor were investigated with detection of Salmonella Typhimurium and Staphylococcus aureus. To demonstrate the practical application, spiked samples of water and orange juice were analysed with acceptable recovery results. The label-free immunosensor exhibits better performance, detection limit (94 CFU/mL), high sensitivity (2.9 nm/1000 CFU mL(-1); 3135 nm/RIU) and profound specificity as compared to conventional fiber optic SPR sensor (detection limit: 391 CFU/mL, sensitivity: 0.6 nm/1000 CFU mL(-1); 1646 nm/RIU). This sensing platform shows promising applications in regular water and food quality monitoring for various pathogenic microorganisms.

In this paper, we have reported the design of the surface plasmon resonance probes prepared from partially etched polymer optical probe and specially tapered single-mode fiber tip probe which are gold coated in magnetron-sputtering unit. The coating parameters and conditions are discussed in details to achieve sensitive surface plasmon resonance probes. The sensor probes work in transmission modes. The gold-coated etched in-line polymer fiber probe demonstrates high sensitivity, ~2459 nm/RIU and working range includes visible to infrared wavelength. The fiber tip probe with very small interaction area demonstrates sensitivity, ~166 nm/RIU. The in-line fiber probe could be used for large volume sample and the pointed fiber tip could be used for small volume samples.

The sensing performance of a tapered fiber optic surface plasmon resonance (SPR) sensor have been studied experimentally and the combined effect of metal layer thickness and taper ratio on the sensor performance have been investigated.

A new approach has been proposed for monolayer plasmonic coating on optical fiber for sensor application. It uses evanescent wave in addition to chemical linker while the chemically treated probe is dip-coated with nanoparticles. The combined technique for monolayer coating on optical fiber increases the packing density of the particles. Formation of densely packed nanoparticle monolayer leads to higher transmission loss and wavelength shifts which is used as surface plasmon resonance-based refractive index sensor. As a proof of the concept, we have prepared a similar probe which has been used as chemical sensor. The sensor significantly improves sensitivity due to increase in packing density and surface area. The sensitivity of the sensor depends upon the formation of the nanoparticle coating. We have demonstrated the probe sensitivity as 987.85 nm/RIU using commonly available chemicals.

In the present study, a surface plasmon resonance (SPR) based fiber optic sensor is proposed. The extreme sensitivity of SPR modes on the surrounding refractive index has been exploited to make the sensor. The optical fiber is coated with gold film which supports the propagation of surface plasmons. The SPR dip in the transmission spectrum is observed and its shift with varying refractive indices of different concentrations of sucrose solutions are obtained. General Terms Photonics, Fiber optic sensors