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Forward scattering is an essential tool for investigating the colloidal suspension of polystyrene microspheres (PSMs). Evanescent wave coupled cavity ringdown spectroscopy (EW-CRDS) shows the anomalous extinction behavior in the limit of PSM particles that is much larger than the wavelength. EW-CRDS is a highly sensitive technique that improves weak absorption signals by enhancing the absorption path length, allowing for probing a range of processes at the solid/liquid interface by assessing the extinction properties. Additionally, it possesses the ability to sense a minimum absorbance of 1.2 × 10−6. EW-CRDS provides sufficient accuracy to detect correlation effects for PSMs in water at the interfacial region and their influence on forward scattering or extinction. In this work, we discuss the impact of volume fraction on the extinction of scatterers composed of microparticles in aqueous media. The findings of this study will contribute to a deeper understanding of the scattering dynamics in colloidal suspensions, with potential applications in various fields, including biology and metrology. [ABSTRACT FROM AUTHOR]

We employed the wavelength-interrogated surface plasmon resonance (SPR) method to characterize the real-time kinetics of urea-urease hydrolysis reaction in response to a CO2-free N2 environment and CO2-enriched ambient reaction medium. We established that a simple label-free SPR probe could accurately extract kinetic parameters from the nature of the sharp jump of the SPR wavelength shift in the reaction profile. The kinetic analysis showed that CO2 production increases with increasing reaction time irrespective of CO2-free N2 or CO2-enriched reaction environment. We also explored the essential insights into the isotopic fractionations of 12CO2, 13CO2, 12C18O16O in the reaction medium utilizing integrated cavity output spectroscopy. The plasmonic system measured the reaction rate in the order of 10-7 M/s for urea species in the presence of the urease enzyme. This study deepens our understanding of plasmonic-based enzymatic urea hydrolysis in real time and opens a new way to quantify chemical reaction kinetics for various other systems. This is the first detailed experimental investigation of the real-time kinetics of urea-urease hydrolysis reaction exploiting wavelength-interrogated surface plasmon resonance method in response to produced CO2 in the CO2-free N2 environment and CO2-enriched ambient reaction medium utilizing integrated cavity output spectroscopy. [ABSTRACT FROM AUTHOR]

Here, we perform a theoretical investigation of the impact of film thickness and incident angle on the surface plasmon resonance spectra for annealed and postannealed Ga-doped ZnO (ZnO:Ga) in a 3-phase Kretschmann configuration. A detailed comparative study has been performed to determine the optimum configuration to be utilized for sensing applications. Though both films are found to support plasmonic excitation for thickness below 200 nm, detection accuracy and sensitivity calculations from the resonance plots simulated in the MATLAB environment reveal that the preference of one over the other should be in accordance with the concerned application. [ABSTRACT FROM AUTHOR]

In this paper, indium tin oxide (ITO) is considered as an alternative plasmonic material beyond conventional plasmon generating metal. A total of 150-nm-thick ITO film-based Kretschmann configuration is demonstrated in NIR region. Minimum possible reflectance with optimum FWHM of resonance plot is the essential criteria for the incident angle selection of the said structure to increase the sensitivity and improve the performance of SPR biosensors in wavelength interrogation mode. Reflectance, phase, and field enhancement curves have been studied for different gaseous samples, and corresponding wavelength sensitivity has been calculated for the change of refractive index of the sample in the order of two. Differential resonance parameters have also been studied which are found to provide increased sensitivity. Theoretical simulation-based results validate that the proposed sensor can provide higher sensitivity by measuring the differential phase. [ABSTRACT FROM AUTHOR]

Highlights • Comparative performance study of mono- and bi-metallic plasmonic sensor. • Ag-Au is more stable and desirable with sensitivity, FWHM and FOM lying between Ag or Au based structure. • Sensitivity using both WS 2 and graphene is higher than single WS 2 or graphene layer. • The number of WS 2 layer is an important factor to affect the performance of the proposed sensor. • Simulation based sensing of glucose in Urine as a bio-sample is also presented. Abstract Theoretical investigation of special types of efficient nanoplasmonic sensors with monometallic and bimetallic Kretschmann configurations using silver and gold has been explored. Conventional Kretschmann structure has been modified using WS 2 or graphene for improving the performance of the sensor. We further show that incorporation of both WS 2 and graphene in the proposed structure is more advantageous. Some interesting theoretical results concerned with sensing of biological sample using this structure have also been presented. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR)-based differential phase analysis has been presented. Real as well as complex plane analysis of resonance parameters have been undertaken for the optimum selection of metal thicknesses in a bimetallic SPR configuration working under both angular and spectral regime. Theoretically, we can characterize the aqueous solution in terms of this differential phase variation due to the variation of sample parameters such as concentration and temperature. In this respect, two case studies, namely, concentration of hemoglobin in human blood and sensing of temperature of water have been demonstrated and proposed theoretically. By monitoring the change of differential phase, proposed approach leads to a very sensitive measurement of concentration and temperature. [ABSTRACT FROM AUTHOR]

Split Mach–Zehnder interferometer is proposed for demonstration of phase modulation of p- and s- polarized beams in a surface plasmon resonance based phase sensitive interference imaging platform. Significant phase change has been observed in Al coated prism based SPR configuration for p-polarized beam, whereas practically no phase change occurs for s-polarized beam. Qualitative analysis of SPR modulated interference fringes also validates the observed effects. A proposed Split Mach–Zehnder set up is shown for simultaneous sensing of two different samples. [ABSTRACT FROM AUTHOR]

We generate a nondiffracted Bessel beam using an axicon. A simple setup is presented to generate a zero order Bessel beam. Moreover, we introduce certain modifications in this optical setup for unconventional generation of an optical vortex beam using an axicon pair and a birefringent lens. An optical vortex beam with a topological charge of 1 is generated, and the corresponding spiral pattern has been demonstrated, which confirms the presence of orbital angular momentum in the optical vortex beam. Further, plasmonic excitation is validated using both zero order and first order Bessel beams. Our approach to confirm the presence of surface plasmon resonance relies on the use of a Wollaston prism. We are able to separately identify the coupling of surface plasmons with the p-polarized components via the absence of the corresponding annular beam. [ABSTRACT FROM AUTHOR]

We report a novel scheme for sensitivity-enhanced liquid phase cavity ring-down spectroscopy (CRDS) exploiting the two-dimensional transition metal dichalcogenides (2D-TMDCs) based surface plasmon resonance (SPR). We investigated the performance of the proposed sensing scheme by monitoring water isotopologues i.e. D 2 O (heavy water) and H 2 O on the SPR chip utilizing a simulation-based characteristics transfer matrix method. The cavity-enhanced SPR coupled with 2D-TMDCs is employed to detect D 2 O from distilled (DI) water with good time response. This proposed approach exhibited minimum sensitivity up to 448 ns/RIU with 4-layers of molybdenum disulfide (MoS 2) and maximum sensitivity up to​ 604 ns/RIU with 4-layers of tungsten diselenide (WSe 2). Moreover, dependence of cavity-finesse and chip-sensitivity on the 2D-nanomaterials suggests that SPR-CRDS is a new-strategy for the applications of plasmonic chemical sensing in the condensed phase with absorbance of the order of 10−11. • Coupling cavity ring-down spectroscopy and surface plasmon resonance with 2D-TMDC to probe condensed-phase molecules. • Performance of the proposed scheme was tested by monitoring various water isotopologues. • Various 2D materials were employed to increase the ring-down sensitivity. [ABSTRACT FROM AUTHOR]

Experimental investigation on surface plasmon resonance (SPR) modulated interference has been proposed and demonstrated under radially sheared environment with the help of a birefringent lens. SPR modulated interference images captured by a charged couple device have been demonstrated in two different analyzing regime, namely, using an analyzer and using a Wollaston prism, the later being advantageous for the simultaneous observation of p- and s-polarized contribution towards SPR. We also report the analysis of the interference imaging for the two substrate materials and also for the two analytes in order to show the substrate-sample dependency of SPR. Moreover, phase dependent resonant behavior, together with the analysis of amplitude reflection co-efficient in complex plane, has been theoretically simulated and discussed in support of the present experimental investigation, which can be well utilized for biological and chemical sensing. [ABSTRACT FROM AUTHOR]

Metallic film thickness optimization in mono- and bimetallic plasmonic structures has been carried out in order to determine the correct device parameters. Different resonance parameters, such as reflectivity, phase, field enhancement, and the complex amplitude reflectance Argand diagram (CARAD), have been investigated for the proposed optimization procedure. Comparison of mono- and bimetallic plasmonic structures has been carried out in the context of these resonance parameters with simultaneous angular and spectral interrogation. Differential phase analysis has also been performed and its application to sensing has been discussed along with a proposed interferometric set-up. [ABSTRACT FROM AUTHOR]