A nonenzymatic reduced graphene oxide-based nanosensor for parathion

Organophosphate-based pesticides (e.g., parathion (PT)) have toxic effects on human health through their residues. Therefore, cost-effective and rapid detection strategies need to be developed to ensure the consuming food is free of any organophosphate-residue. This work proposed the fabrication of a robust, nonenzymatic electrochemical-sensing electrode modified with electrochemically reduced graphene oxide (ERGO) to detect PT residues in environmental samples (e.g., soil, water) as well as in vegetables and cereals. The ERGO sensor shows a significantly affected electrocatalytic reduction peak at -0.58 V (vs Ag/AgCl) for rapid quantifi-cation of PT due to the amplified electroactive surface area of the modified electrode. At optimized experimental conditions, square-wave voltammetric analysis exhibits higher sensitivity (50.5 mu A center dot mu M-1 center dot cm(-2)), excellent selectivity, excellent stability (approximate to 180 days), good reproducibility, and repeatability for interference-free detection of PT residues in actual samples. This electro-chemical nanosensor is suitable for point-of-care detection of PT in a wide dynamic range of 3 x 10(-11)-11 x 10(-6) M with a lower detection limit of 10.9 pM. The performance of the nanosensor was validated by adding PT to natural samples and comparing the data via absorption spectroscopy. PT detection results encourage the design of easy-to-use nanosensor-based analytical tools for rapidly monitoring other environmental samples

Deflection of light in equatorial plane due to Kerr-Taub-NUT body

According to General Relativity, there are factors like mass, rotation, charge and presence of Cosmological constant that can influence the path of light ray. Apart from these factors, many authors have also reported the influence of gravitomagnetism on the path of light ray. In this study we have discussed the effect of a rotating Kerr-Taub-NUT body where the strength of the gravitomagnetic monopole is represented by the NUT factor or magnetic mass. We use the null geodesic of photon method to obtain the deflection angle of light ray for a Kerr-Taub-NUT body in equatorial plane upto the fourth order term. Our study shows that the NUT factor has a noticeable effect on the path of the light ray. By considering the magnetism to be zero, the expression of bending angle gets reduced to the Kerr bending angle. However, we obtained a non-zero bending angle for a hypothetical massless, magnetic body

A new diagnostic tool for measuring total antioxidants in tea

The purpose of this research was to develop a sensory system to measure antioxidant level in tea with a view to assessing the quality of different grades of tea available in the market. We proposed an easy, reliable sensory system to quantify the total antioxidant capacity (TAC) of tea infusion. A preformed ABTS [2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate)] radical cation (ABTS(+)) was used in the bulk electrolyte in presence of glassy carbon (GC) or platinum (Pt) working electrode. Total antioxidant present in sample was determined by amperometric response at optimum redox potential of 0.552 V dictated by cyclic voltammogram. Linear calibrations for standard antioxidants such as gallic acid, caffeic acid, ascorbic acid, catechin hydrate and chlorogenic acid were obtained in the range of 1-250 mu g/mL. Quantitative estimation of antioxidants in tea samples were expressed as gallic acid equivalent (GAE) with a detection limit of 2.34 mu g/mL. The amperometric sensor showed optimum response at pH 5.8 at around 25 degrees C. Excellent correlations were obtained with standard spectrophotometric assays. The system might be useful for quality control of various grades of tea due to its specificity, simplicity and quick response of measurement procedures. The present research gave excellent opportunity to grade tea on the basis of antioxidant levels. Similarly the system might have useful applications in determining antioxidants in other common food items such as fruit juices and other beverages

A simple electrochemical approach to fabricate functionalized MWCNT-nanogold decorated PEDOT nanohybrid for simultaneous quantification of uric acid, xanthine and hypoxanthine

Medical diagnostics and detection of food spoilage require estimation of hypoxanthine (HX), xanthine (XN), and uric acid (UA). A selective sensing platform has been proposed for simultaneous detection of all these species. Functionalized multi-walled carbon nanotube (fMWCNT) stabilized nanogold decorated PEDOT:TOS polymeric nanocomposite (Au-PEDOT-fMWCNT) was synthesized through rapid one-step electropolymerization to enhance conductivity and active surface area by several folds. Electrochemical activities of the proposed sensing platform were analyzed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS). Analyses through SEM, FESEM and TEM were performed to explore the surface morphology and elemental analysis of the polymeric nanohybrid was investigated by XPS, Raman, FTIR, XRD spectroscopy. Electro-catalysis of UA, XN and HX occurred at low oxidation potentials i.e. 0.082, 0.463 and 0.808 V, respectively in the optimized conditions. The uniquely designed simple, interference free Au-PEDOT-fMWCNT/GCE sensor exhibited high selectivity, good reproducibility, reusability (similar to 180 times) and stability (similar to 3 month) with excellent sensitivity of 1.73, 14.31 and 3.82 mu A mu M-1 cm(-2) for UA, XN and HX, respectively. The sensor exhibited linear ranges of detection as 0.1-800, 0.05-175 and 0.1-150 mu M with detection limits of 199.3, 24.1 and 90.5 nM for quantification of UA, XN and HX respectively. The performance of the proposed sensor was validated by addition of UA, XN and HX in human serum, urine and fish samples by comparing to those using HPLC. The results indicated good applicability of the proposed sensor for simultaneous detection of UA, XN, HX in real biological fluids. (C) 2020 Elsevier B.V. All rights reserved

Subtle Change in the Charge Distribution of Surface Residues May Affect the Secondary Functions of Cytochrome c

Although the primary function of cytochrome c (cyt c) is electron transfer, the protein caries out an additional secondary function involving its interaction with membrane cardiolipin (CDL), its peroxidase activity, and the initiation of apoptosis. Whereas the primary function of cyt c is essentially conserved, its secondary function varies depending on the source of the protein. We report here a detailed experimental and computational study, which aims to understand, at the molecular level, the difference in the secondary functions of cyt c obtained from horse heart (mammalian) and Saccharomyces cerevisiae (yeast). The conformational landscape of cyt c has been found to be heterogeneous, consisting of an equilibrium between the compact and extended conformers as well as the oligomeric species. Because the determination of relative populations of these conformers is difficult to obtain by ensemble measurements, we used fluorescence correlation spectroscopy (FCS), a method that offers single-molecule resolution. The population of different species is found to depend on multiple factors, including the protein source, the presence of CDL and urea, and their concentrations. The complex interplay between the conformational distribution and oligomerization plays a crucial role in the variation of the pre-apoptotic regulation of cyt c observed from different sources. Finally, computational studies reveal that the variation in the charge distribution at the surface and the charge reversal sites may be the key determinant of the conformational stability of cyt c