Ayushi Paliwal

Optical properties of WO3 thin films using surface plasmon resonance technique

Indigenously assembled surface plasmon resonance (SPR) technique has been exploited to study the thickness dependent dielectric properties of WO3 thin films. WO3 thin films (80 nm to 200 nm) have been deposited onto gold (Au) coated glass prism by sputtering technique. The structural, optical properties and surface morphology of the deposited WO3 thin films were studied using X-ray diffraction, UV-visible spectrophotometer, Raman spectroscopy, and Scanning electron microscopy (SEM). XRD analysis shows that all the deposited WO3 thin films are exhibiting preferred (020) orientation and Raman data indicates that the films possess single phase monoclinic structure. SEM images reveal the variation in grain size with increase in thickness. The SPR reflectance curves of the WO3/Au/prism structure were utilized to estimate the dielectric properties of WO3 thin films at optical frequency (λ = 633 nm). As the thickness of WO3 thin film increases from 80 nm to 200 nm, the dielectric constant is seen to be decreasin...

Detection of Neisseria meningitidis using surface plasmon resonance based DNA biosensor

Herein, we report the development of a surface plasmon resonance (SPR) based biosensor for the detection of Neisseria meningitidis DNA employing Kretschmann configuration. Highly c-axis oriented ZnO thin film of thickness 200nm was deposited on gold coated glass prisms by RF sputtering technique. Single stranded probe DNA was immobilized on the surface of ZnO thin film by physical adsorption method. SPR reflectance curves were recorded as a function of incident angle of He-Ne laser beam using a laboratory assembled SPR setup. The prepared biosensor exhibits a linear response towards target meningitidis DNA over the concentration range from 10 to 180 ng/μl with a high sensitivity of about 0.03°/(ng/μl) and a low limit of detection of 5 ng/μl. The SPR biosensor demonstrated high specificity and long shelf life thus, pointing towards a promising application in the field of meningitidis diagnosis.

Plasmonic assisted enhanced photoresponse of metal nanoparticle loaded ZnO thin film ultraviolet photodetectors

An ultraviolet (UV) photodetector exhibiting enhanced response characteristics has been realized successfully after integrating various metal nanoparticles (NPs) such as silver (Ag), gold (Au) and platinum (Pt) with sol–gel derived ZnO thin film (NPs–ZnO). The metal NP based photodetector (Ag, Au, Pt-NPs–ZnO) exhibits a relatively high photoresponse in comparison to the bare ZnO based UV photodetector and gives a maximum value of about 4.27 × 103. The combined effect of the lowering of dark current due to the formation of a Schottky barrier at the interface of the metal NPs with the ZnO thin film and the photocurrent upon UV illumination due to the plasmonic effect of loaded NPs results in an enhanced photoresponse of the prepared metal NP–ZnO photodetector. The trapping of incident UV radiation mainly through the enhanced optical absorption by loaded metal NPs due to the plasmonic effect and subsequent coupling of harvesting photons into underlying optical modes of the surface of photoconducting ZnO thin films lead to a significant increase in photocurrent. The observed results provide an indication that the plasmonic assisted UV response of the novel metal NP–ZnO photodetector might provide a breakthrough for the development of next generation photodetectors.

Complex dielectric constant of various biomolecules as a function of wavelength using surface plasmon resonance

Present study focuses on determination of complex dielectric constant of biomolecules as function of frequency by means of surface plasmon resonance (SPR) technique without losing their biofunctionality. Surface plasmon modes have been excited in Kretschmann configuration at interface of ZnO-Au thin films. Various biomolecules (glucose oxidase, cholesterol oxidase, urease, and uricase) have been immobilized successfully on surface of ZnO thin film by electrostatic interaction. SPR reflectance curves for all biomolecules were recorded separately at different wavelengths (407–635 nm). Complex dielectric constant was determined by fitting the experimental SPR data with Fresnels equations. Dielectric constant of all biomolecules shows frequency dispersion and attributed to ionic polarization.

Surface plasmon resonance study on the optical sensing properties of tin oxide (SnO2) films to NH3 gas

Surface plasmon resonance (SPR) technique is an easy and reliable method for detecting very low concentration of toxic gases at room temperature using a gas sensitive thin film layer. In the present work, a room temperature operated NH3 gas sensor has been developed using a laboratory assembled SPR measurement setup utilising a p-polarized He-Ne laser and prism coupling technique. A semiconducting gas sensitive tin oxide (SnO2) layer has been deposited under varying growth conditions (i.e., by varying deposition pressure) over the gold coated prism (BK-7) to excite the surface plasmon modes in Kretschmann configuration. The SPR reflectance curves for prism/Au/SnO2/air system for SnO2 thin films prepared at different sputtering pressure were measured, and the SnO2 film deposited at 10 mT pressure is found to exhibit a sharp SPR reflectance curve with minimum reflectance (0.32) at the resonance angle of 44.7° which is further used for sensing NH3 gas of different concentration at room temperature. The SPR r...

Table top surface plasmon resonance measurement system for efficient urea biosensing using ZnO thin film matrix.

Abstract. The present report addresses the application of surface plasmon resonance (SPR) phenomenon for urea sensing. The former promises a high sensitivity, label-free detection, and real-time information by monitoring the refractive index change at the metal–dielectric interface. In the present report, a highly sensitive urea biosensor has been developed by integrating a ZnO thin film matrix with the SPR technique. Kretschmann configuration has been used to excite the surface plasmon (SP) modes at the ZnO–metal (gold) interface using an indigeneously developed table top SPR measurement setup. Urease (Urs), the urea-specific enzyme, has been immobilized on the surface of ZnO thin film by physical adsorption technique. The SPR reflectance curves were recorded for the prism/Au/ZnO/Urs system in angular interrogation mode with phosphate-buffered saline (PBS) solution as the liquid media. The SPR resonance angle is found to be shifted toward a lower angle from 49.1 to 42.0 deg with an increase in the urea concentration (0 to 300  mg/dl) in the PBS solution. The developed sensor (prism/Au/ZnO/Urs) is found to be highly sensitive [sensitivity=0.039  deg/(mg/dl) or 203  deg/RIU] with detection accuracy of 0.045(deg)−1.

Long range surface plasmon resonance (LRSPR) based highly sensitive refractive index sensor using Kretschmann prism coupling arrangement

Long range surface plasmon resonance (LRSPR) when exploited for sensing purpose exhibit less losses in comparison to the sensors based on conventional SPR technique leading to the development of highly sensitive refractive index sensor. In order to excite long range surface plasmon (LRSP) mode, a high refractive index prism is used as coupler and a thin metal layer is sandwiched between a dielectric having similar refractive index with that of another semi-infinite dielectric. LRSP mode has been excited in symmetric configuration where metal (Au) layer is sandwiched between the two similar refractive index dielectrics (LiF thin film and a fixed concentration of sugar solution) for realization of a refractive index sensor. When the concentration of sugar solution is slightly increased from 30% to 40%, the LRSPR angle increases from 64.6° to 67.9° and the sensor is found to be highly sensitive with sensitivity of 0.0911 °/(mg/dl).

Surface Plasmon Resonance Based Optical NOx Gas Sensor

An indigenously assembled surface plasmon resonance technique have been used for development of an efficient, fast and reversible optical NOx gas sensor operating at room temperature exploiting WO3 as a sensing layer.

Refractive Index Sensor Using Long-Range Surface Plasmon Resonance with Prism Coupler

Long-range surface plasmon resonance (LRSPR)-based sensors exhibit high sensitivity as compared to the conventional SPR sensors due to low losses. A high refractive index prism and low refractive index dielectrics are required to excite long-range surface plasmon (LRSP) mode. In this work, a symmetrical structure consisting of metal (Au) layer sandwiched between the two similar refractive index dielectrics has been utilized to excite LRSPR modes. Two dielectrics, i.e., LiF and MgF2 thin films have been chosen for glucose sensing. Theoretical simulations for optimizing the thickness of two dielectrics have been carried out. Highly sensitive refractive index sensors based on LRSPR have been developed using the two dielectric thin films and their sensitivities have been compared.

Surface plasmon resonance based electro optic measurement of SBN thin films

Strontium Barium Niobate (SBN) has been known for its highest electro optic coefficient amongst the known photorefractive materials. SBN thin films were prepared using Pulsed Laser Deposition (PLD) technique on the conducting LSCO coated Si Substrate and its tetragonal tungsten bronze structure was confirmed using X-ray diffraction technique. Surface Plasmon Resonance (SPR) technique has been effectively used by exploiting the SBN thin film in Otto configuration using prism coupling technique. The SPR reflectance curves for prism/air-gap/gold/SBN/LSCO/Si system were obtained by varying the applied electric field from 0 to 150kV/cm. A continuous increase in minimum reflectance of SPR curves with increase in the electric field across the SBN thin film has been obtained indicating variation in optical properties of SBN thin film on application of electric field. This increase in reflectance was attributed to the change in propagation constant of wave vector due to the change of optical properties of the film under consideration. The resonance condition changes hence the SPR minimum reflectance angle and position changes.