Monika Srivastava

A chitosan-based polyaniline–Au nanocomposite biosensor for determination of cholesterol

A polyaniline–gold (PAni–Au) nanocomposite is chemically synthesized and impregnated in a chitosan matrix for immobilization of cholesterol oxidase on an indium tin oxide-coated glass plate for development of cholesterol biosensors. The PAni–Au nanocomposite is characterized for structural and thermal properties. Further the PAni–Au nanocomposite is used for cholesterol oxidase immobilization and linkage is examined by FTIR. The nanocomposite is used to form a modified bioelectrode by immobilizing cholesterol oxidase in the chitosan matrix and examined under an optical microscope for uniformity and morphological studies. A modified bioelectrode (ChOx/PAni–Au–CH/ITO) is used to detect cholesterol by using a voltammetric technique with a redox mediator. The sensor exhibits linearity in a wide range of 50–500 mg dL−1 with a detection limit of 37.89 mg dL−1, a sensitivity of 0.86 μA mg dL−1 and a shelf life of more than 3 weeks when stored at 4 °C. Voltammetric studies have also been carried out with common possible interferents. Responses are recorded to get enzyme–substrate kinetics for the biosensor and found as Km = 10.84 mg dL−1. The low value of Km indicates that the prepared nanocomposite facilitates the enzymatic reaction and enzymatic activity. Excellent immobilization and enzyme–substrate reactions show a distinct advantage of this matrix over other matrixes used for cholesterol biosensors. The novelty of the prepared electrode lies in its reusability, higher sensitivity, better shelf life, and accuracy.

Functional graphene–gold nanoparticle hybrid system for enhanced electrochemical biosensing of free cholesterol

Realizing the unavailability of fast and reliable diagnostic techniques, especially for cholesterol measurement, the present work reports the development of cost effective bioelectrodes based on a reduced graphene oxide–functionalized gold nanoparticle (∼25 nm) hybrid system (RGO–Fn Au NPs). The electrodes fabricated by the electrophoretic deposition technique attest a synergistically enhanced electrochemical sensing ability of 193.4 μA mM−1 cm−2 for free cholesterol detection, which is much higher than that of the traditional RGO system. The electrochemical impedance studies (EIS) show low charge transfer resistance, RCT, for the hybrid system which is 57% and 60% lower than those of RGO and Au NPs respectively. Also higher loading capacity and enhanced kinetics have been realized for the hybrid system, owing to lower Km value (0.005 mM) and enhanced rate constant (3.8 × 10−4 cm s−1) in comparison with RGO and Au NPs. Moreover, the RGO–Fn Au NP platform promises a wider range of cholesterol detection (0.65–12.93 mM), while simultaneously being capable of detecting as low as 0.34 mM of free cholesterol. Apart from better sensitivity, loading capacity, kinetics and detection range, the system also has appreciable selectivity and stability. This supports its potential to be brought on field in the near future for cost effective and reliable detection from the complex system of human serum.

A comparative Study of Aptasensor Vs Immunosensor for Label-Free PSA Cancer Detection on GQDs-AuNRs Modified Screen-Printed Electrodes

Label-free and sensitive detection of PSA (Prostate Specific Antigen) is still a big challenge in the arena of prostate cancer diagnosis in males. We present a comparative study for label-free PSA aptasensor and PSA immunosensor for the PSA-specific monoclonal antibody, based on graphene quantum dots-gold nanorods (GQDs-AuNRs) modified screen-printed electrodes. GQDs-AuNRs composite has been synthesized and used as an electro-active material, which shows fast electron transfer and catalytic property. Aptamer or anti-PSA has immobilized onto the surface of modified screen printed electrodes. Three techniques are used simultaneously, viz. cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedence spectroscopy (EIS) to investigate the analytical performance of both PSA aptasensor and PSA immunosensor with its corresponding PSA antigen. Under optimum conditions, both sensors show comparable results with an almost same limit of detection (LOD) of 0.14 ng mL−1. The results developed with aptasensor and anti-PSA is also checked through the detection of PSA in real samples with acceptable results. Our study suggests some advantages of aptasensor in terms of better stability, simplicity and cost effectiveness. Further our present work shows enormous potential of our developed sensors for real application using voltammetric and EIS techniques simultaneous to get reliable detection of the disease.

Application of Unsaturated Fatty Acid Molecules Derived from Microalgae toward Mild Steel Corrosion Inhibition in HCl Solution: A Novel Approach for Metal–Inhibitor Association

Fatty acid molecules 9,12,15-octadecatrienoic acid (C18:3), 9,12-octadecadienoic acid (C18:2), and hexadecanoic acid (C16:0) possessing active functional groups with the capability of fast electron transfer have been established for effective corrosion inhibition of mild steel. In this regard, a microalga Scenedesmus sp. is isolated and its fatty acids have been studied to corroborate the adsorption behavior, attributing the anticorrosion efficacy on mild steel in 1 M HCl solution by forming metal–inhibitor framework. Electrochemical analysis has been used to ascertain the surpassing corrosion inhibition efficiency at an optimal concentration of 36 ppm with maximum 95.1% inhibitive performance. The results of metallography with or without the inhibitor molecules have indicated significant changes in surface morphology of mild steel specimen for gradual enhancement in immersion time (72 h). Hydrogen evolution reaction has been emphasized to observe the tendency of significant decrease in the bubble formation in the presence of inhibitor compared to 1 M HCl solution only. Surface morphometric studies (scanning electron microscopy and atomic force microscopy) have also revealed the excellent adsorption capacity of Scenedesmus fatty acids on metal surface. Quantum chemical calculations, performed by density functional theory, determined significant adsorption effectiveness, based on the donor–acceptor capability between metallic surface and inhibitor molecules.