Sandeep K. Sharma

Biomolecules for development of biosensors and their applications

Biosensors are analytical devices incorporating biological materials such as enzymes, tissues, microorganisms, antibodies, cell receptors or biologically derived materials or a biomimic component intimately associated with or integrated within a physicochemical transducer or transducing microsystem which may be either optical, electrochemical, thermometric, piezoelectric or magnetic. The electronic signals produced are proportional to the concentration of specific analyte. A biomaterial may be any material, natural or man-made, that comprises whole or part of a living structure or biomedical device, which performs natural function. An essential component of molecular sensor is reagent layers. Creation of these layers require the immobilization of recognition elements for the detection method. The recognition elements are biomolecules. Laboratory methods of immobilization are numerous, but may not always appropriate for manufacture of biosensors. In the present article, we describe the use of various biomaterials for biosensors as well as their availability.

A quick and simple biostrip technique for detection of lactose

A quick, simple and economical biostrip technology was developed for estimation of lactose by immobilizing β-galactosidase, galactose oxidase and horseradish peroxidase on to a polymeric support. The biostrip is dipped in milk or milk products and, from the colour that develops from an added chromogen, the concentration of lactose can be estimated from < 20 to 100+g l−1. The biostrips may be used in dairy industries, hospitals and remote areas where expensive instruments are not available.

Biogenic synthesis of metal nanocatalysts using Mimosa pudica leaves for efficient reduction of aromatic nitrocompounds

Phytochemicals present in Mimosa pudica (M.pudica) leaves extract exhibit the potential for biogenic reduction of Ni, Co and Cu ions to their respective base metal nanoparticles (NPs) in a single-step. This approach of NP synthesis mediated by plant extract is environmentally benign and totally an aqueous phase green synthetic approach. The so-synthesised metallic NPs have identical spherical shape with an average diameter of about 8 nm as determined from TEM images. The ensuing particles have been utilized as nanocatalysts for the reduction of aromatic nitro compounds, p-nitrophenol and p-nitroaniline, using sodium borohydride (NaBH4). Both reactions are extremely slow in the absence of a catalyst. From the kinetic data, the rate constants for both the catalyzed reactions exhibit an interesting order: kCu NPs > kCo NPs > kNi NPs. These variations in catalytic performance of the NPs have been attributed to the difference in their work function values.

Dry-reagent strips for testing milk pasteurization

Biostrips have become more popular for diagnosis of various diseases as well as for testing of different chemical and biochemical parameters. Alkaline phosphatase (ALP) is an enzyme naturally present in raw milk, which is used as an indicator for proper milk pasteurization. Nonpasteurized or raw milk contains ALP, which causes intra-abdominal bacterial infection after drinking the milk, whereas after pasteurization, ALP is denatured. Therefore, milk industries test the milk after pasteurization using conventional methods such as colorimetric and fluorescence. Our attention was drawn to develop quick, simple and economical test using dry-reagent strips for detection of ALP activity in milk. It is based on ALP reaction with p-nitrophenyl phosphate in the presence of water to liberate p-nitrophenol and inorganic phosphate. p-Nitrophenol on reacting with a specific chromogen changes the colour of the strip from light blue to green, which is visualized by the naked eyes. The strip has a sensitivity of >0.5 units/L. The strips may be used in dairy industries and remote areas where expensive instruments are not available. The strip is stable for more than a year at room temperature.

Lactose Biosensor Based on Lactase and Galactose Oxidase Immobilized in Polyvinyl Formal

A lactose biosensor was developed by immobilizing lactase and galactose oxidase in a polyvinyl formal membrane and was attached to the oxygen electrode of a dissolved oxygen analyzer for estimation of lactose in milk and food products. The enzyme immobilized polyvinyl formal membrane was characterized by atomic force microscopy. The biosensor showed the linearity for 1–7 g dl−1 of lactose and can be reused for up to 20 measurements. The effects of pH, temperature and the stability of the immobilized lactase and galactose oxidase in PVF membrane were also studied. The enzyme membrane was found stable up to 35°C and had a shelf-life of more than three months at 4°C.

Magnetic iron oxide nanoparticles encapsulating horseradish peroxidase (HRP): synthesis, characterization and carrier for the generation of free radicals for potential applications in cancer therapy

This article reports a method of preparation of iron oxide nanoparticles using a reverse micellar (water-in-oil) approach. We have encapsulated horseradish peroxidase (HRP) in iron oxide nanoparticles. HRTEM, XRD, and DLS analyses showed that the average diameter of these particles was around 20 nm, 20.5 nm, and 30 nm, respectively, and the particles were highly monodispersed with spherical morphology. The entrapment efficiency of HRP was found to be as high as 92%. Practically, the entrapped enzyme shows zero leachability for up to 30 days. Enzyme entrapped in iron oxide nanoparticles followed Michaelis–Menten kinetics and showed higher stability towards temperature change as compared to free enzyme. Entrapped enzyme is stable at up to 65 °C; however, the free enzyme starts to lose its activity above 38 °C. The entrapped enzyme, HRP, has been used to convert a benign prodrug, indole-3-acetic acid (IAA), to a toxic oxidized product, and its toxic effect has been tested on cancerous cell lines through thiazolyl blue tetrazolium blue (MTT) assay. MTT assay on two cancer cell lines revealed that indole acetic acid (IAA), the prodrug alone, had no cytotoxic effect, and it became active only after oxidative decarboxylation by HRP. The benign substrate IAA reaches the cells and is oxidized by HRP. IAA, on reacting with HRP, forms free radicals such as indolyl, skatole and peroxyl radicals. This creates severe oxidative stress in the cancer cells, resulting in cell death.

Thermodynamic and electrochemical study of multicomponent polymer complexes of varying composition

Abstract Multicomponent complexes of varying composition have been prepared from poly(methacrylic acid-co-acrylamide), poly(ethyleneimine) and poly(vinylpyrrolidone). Stability constants and related thermodynamic parameters have been determined. Interpretations have been sought in terms of secondary binding forces and their magnitude.

PV Generator Driven First Order Circuit - Transient Analysis using LambertWFunction

The study of dynamic behaviour of circuits containing one or more energy-storing circuit elements powered by photovoltaic (PV) generator has been an intriguing aspect to the PV module design engineer. A PV module constitutes a special power source that has a transcendental current-voltage relationship. As can be expected this makes the transient re- sponse analysis for such circuits far more complicated than the conventional power source. Methods and models have been suggested to study the transient behaviour of such circuits. Earlier works on first order circuits have assumed that there are no current leakage losses in the form of Shunt resistance for a PV generator. In absence of an exact closed form solution for the transcendental current-voltage relations of a PV generator, these methods approximately describe the tran- sient behaviour both quantitatively and qualitatively. Here we present an approach that uses exact closed form solutions based on Lambert W function, having incorporated finite value of shunt resistance for the PV generator.

Reflectance measurement of the CdZnTe surfaces below and above the damage threshold value

When sufficient intense laser pulse interacts with semi-conductors, permanent damage results due to formation of scattering centers in the semi-conductor surface. Reflectance of the damaged surface is reduced as compared to the smooth surface. Generally, damage threshold is defined as a value for which the reflectance is decreased by more than 10%. It is interesting that reflectance change can be seen below the damage threshold value. In the present work it has been shown that these changes occur at the rate of 0.5% per pulse. These changes are not due to any type of irreversible process in the material and slow but continuous decrease can be seen in the reflectance if the number of pulses is increased. Although when the fluence is increased, remarkable change can be seen in the reflectance decrease for the first pulse (in some cases, for 2-3 pulses), but if the number of incident pulses are further increased, the slow and continuous decrease is shown in reflectance value. The present experiments were performed in the CdZnTe <111> single crystal surface exposed to Nd:YAG laser (pulse duration: 20ns, prs:1pps, wavelength: 1.064µm) in the ambient air.

Thermodynamical study on the formation of some bivalent metal complexes of biologically active N,N′-di-p-tolyl-5-nitro-2-thiobarbituric acid (DTNTBA) in aqueous solutions

Thermodynamic proton-ligand stability constants of N,N′-di-p-tolyl-5-nitro-2-thiobarbituric acid (DTNTBA) and the thermodynamic metal ligand stability constants of complexes of DTNTBA with some bivalent metal ions were determined by potentiometric measurements in 75% (v/v) aqueous dioxan medium at different temperatures, ranging from 20 to 50°C. The order of stability constants was found to be Cu2+ > Ni2+ > Co2+ > Zn2+ > Cd2+ > Mn2+ > Mg2+. The values of Smin (χ2) also been calculated. The thermodynamic functions along with the error range for the stepwise complexation processes were calculated at 20°C (error range ±0.5°C). The process is predominantly an enthalpy-driven process.