Mediator-free total cholesterol estimation using a bi-enzyme functionalized nanostructured gold electrode

We report the fabrication of a bi-enzyme functionalized nanostructured Au electrode for the mediator-free determination of total cholesterol. A one-step electrochemical route for the synthesis, functionalization and deposition of Au nanostructures via the electroreduction of gold chloride onto indium tin oxide (ITO) coated glass plates has been proposed. The covalent biofunctionalization of the optimized Au electrode was done with cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) to investigate the kinetic parameters and the sensing characteristics. The ChEt-ChOx/Glu-NanoAu/ITO bioelectrode has a surface-controlled electrode reaction with an electron transfer coefficient and a charge transfer rate constant of 0.68 and 7.09 s(-1), respectively. Under the optimal conditions, the bioelectrode undergoes a direct electron transfer reaction and exhibits a high sensitivity of 0.53 mA mM(-1) cm(-2) and a low detection limit of 1.57 mu M for cholesterol ester without the use of any redox mediator. In addition, the kinetic analysis reveals that the bioelectrode exhibits a surface concentration of 8.82 x 10(-12) mol cm(-2). The sensor has also been validated with clinical samples. The proposed biosensor shows good sensitivity, stability and selectivity towards total cholesterol and may thus find implications in the fabrication of biosensing devices

A single molecule switch based on two Pd nanocrystals linked by a conjugated dithiol

Tunneling spectroscopy measurements have been carried out on a single molecule device formed by two Pd nanocrystals (dia, $\sim$5 nm) electronically coupled by a conducting molecule, dimercaptodiphenylacetylene. The I-V data, obtained by positioning the tip over a nanocrystal electrode, exhibit negative differential resistance (NDR) on a background M-I-M characteristics. The NDR feature occurs at $\sim$0.67 V at 300 K and shifts to a higher bias of 1.93 V at 90 K. When the tip is held in the middle region of the device, a coulomb blockade region is observed ($\pm\sim$0.3 V).Comment: Accepted in Praman

Surfactant-promoted formation of fractal and dendritic nanostructures of gold and silver at the organic-aqueous interface

The effect of surfactants such as tetraoctylammoniumbromide (TOAB) and cetyltrimethylammoniumbromide (CTAB) on the type of nanostructures formed when gold ions present in the organic phase are reduced at the interface by hydrazine in the aqueous phase has been investigated. Extended fractal structures are formed at the liquid-liquid interface, the fractal structures themselves comprising cauliflower type units formed by gold nanorods. Accordingly, the nanostructures exhibit transverse and longitudinal plasmon adsorption bands in the 550 and 800 nm regions, respectively. Dendritic structures of silver are formed at the interface when Ag ions are reduced similarly in the presence of surfactants. The nanostructures consist of nanoparticles or nanorods with five-fold symmetry

Nanocrystals of metals, semiconductors and oxides: novel synthesis and applications

Films of nanocrystals such as Au, Ag and Pd, semiconducting sulphides such as CdS, ZnS and CoS, and oxides such as Fe2O3 and CuO have been prepared by employing reactions at liquid-liquid (organic-aqueous) interfaces. In this method, a suitable organic derivative of the metal taken in the organic layer reacts at the interface with the appropriate reagent present in the organic layer. Two typical applications of nanocrystals pertaining to magnetic devices and dip-pen lithography are briefly presented

Fiber optics based surface plasmon resonance for label-free optical sensing

349-362With the advancement in the laser technology and availability of low cost optical fibers, there is an increasing trend towards adoption of optical fibers as sensing element for development of optical sensors probes especially point-of-care sensing for environmental, biomedical and clinical application. Refractive index measurement through surface plasmon resonance has evolved to be, one of the most sensitive transducer for label-free sensing with high sensitivity. Surface plasmon resonance is a surface sensitive optoelectronic phenomenon, where light incident on a plasmonic metal surface at a given angle can excite a surface-bound electromagnetic wave, a surface plasmon. Associated with the surface plasmon is an evanescent field that probes local changes in the refractive index of the ambient medium that are used for monitoring analyte- supramolecular/ bio-molecular ligand interactions. Present review outlines a concise view on theoretical aspects of fiber optics based surface plasmon resonance phenomenon and comprehensive updated review on research and development for progression in the design of fiber optics based SPR sensors

Electroactive Prussian Blue Encapsulated Iron Oxide Nanostructures for Mediator-Free Cholesterol Estimation

Iron oxide nanoparticles of size similar to 10 nm have been encapsulated into four nanometer thick shells of Prussian blue and were then electrophoretically deposited onto an indium tin oxide substrate. The immobilization of cholesterol oxidase has been done onto the nanostructured film to investigate the kinetic parameters and biosensing characteristics. The fabricated bioelectrode exhibits an electron transfer coefficient and a charge transfer rate constant of 0.45 and 45.15 s(-1), respectively. Direct electron transfer properties of the nanostructured film result in 3rd generation cholesterol biosensor. The bioelectrode exhibits high sensitivity (2.15 mAM(-1)cm(-2)), a low K-m(app) value (0.07 mM), good stability and high selectivity towards cholesterol

Fiber optics based surface plasmon resonance for label-free optical sensing

349-362With the advancement in the laser technology and availability of low cost optical fibers, there is an increasing trend towards adoption of optical fibers as sensing element for development of optical sensors probes especially point-of-care sensing for environmental, biomedical and clinical application. Refractive index measurement through surface plasmon resonance has evolved to be, one of the most sensitive transducer for label-free sensing with high sensitivity. Surface plasmon resonance is a surface sensitive optoelectronic phenomenon, where light incident on a plasmonic metal surface at a given angle can excite a surface-bound electromagnetic wave, a surface plasmon. Associated with the surface plasmon is an evanescent field that probes local changes in the refractive index of the ambient medium that are used for monitoring analyte- supramolecular/ bio-molecular ligand interactions. Present review outlines a concise view on theoretical aspects of fiber optics based surface plasmon resonance phenomenon and comprehensive updated review on research and development for progression in the design of fiber optics based SPR sensors

Advancing frequency fine-tuning: a theoretical approach to a novel metamaterial-inspired Bi-layer resonator

This study presents a novel adjustable device designed for precise frequency tuning within the S-band of the microwave spectra. In addition to the geometrical design and dielectric behavior of the resonator, this study identifies an influential governing factor that affects the resonant frequency. The proposed method utilizes a bi-layer split ring resonator configuration implemented on a $4\times 4\,{\rm{cm}}$ FR4 epoxy substrate with a dielectric constant of 4.4. The substrate is coated with a 35 μ m- thick layer of copper and patterned as split ring resonator. Frequency tuning was achieved by spatially separating the two parallel split ring resonators in increments of 800 μ m. This innovative approach allows for a shift in the resonant frequency range from 2.36 GHz to 2.61 GHz, covering the desired frequencies in the S-band for applications such as biomedical and wireless communications. This study demonstrates that the alteration in the frequency domain is dependent on the distance between the two layers of split ring resonators. Compared to existing frequency tuning mechanisms, this adjustable bi-layer split ring resonator offers numerous advantages including simplicity, cost-effectiveness, and high sensitivity. The research employs a combination of finite-element simulations and theoretical analysis to validate the findings