Chandra Mouli Pandey

Acetylthiocholine/acetylcholine and thiocholine/choline electrochemical biosensors/sensors based on an organically modified sol–gel glass enzyme reactor and graphite paste electrode

Abstract Electrochemical sensors for acetylthiocholine and acetylcholine are described. The non-mediated electrochemistry of acetylthiocholine and thiocholine is studied on the surface of graphite paste electrode and results show that acetylthiocholine is directly oxidized/reduced at >0.32 V vs. Ag/AgCl in both acidic and basic medium. In basic medium, both cathodic and anodic peak currents are less as compared to that of the same amount in acidic medium, which shows that the kinetics of non-enzymatic hydrolysis of acetylcholine into electroactive thiocholine is faster in acidic medium and slower in basic medium. Thiocholine is directly oxidized/reduced at >0.35 V vs. Ag/AgCl with relatively larger anodic current compared to cathodic peak current similar to that of acetylcholine results recorded in acidic medium (pH 6.0). The electrochemical sensor/biosensors for acetylthiocholine/acetylcholine and thiocholine/choline are developed using two enzyme reactors: (1) acetylcholinesterase (AChE) encapsulated organically modified sol–gel glass, and (2) choline oxidase (ChO) immobilized within mediators (tetracyanoquinodimethane (TCNQ), tetrathiafulvalene (TTF), and dimethyl ferrocene (dmFc))-modified graphite paste electrodes. The AChE-immobilized into organically modified sol–gel glass behaves as the reactor for enzymatic hydrolysis of acetylthiocholine/acetylcholine into thiocholine/choline, whereas mediator- and ChO-modified paste electrodes are used for the detection of thiocholine/choline through mediated mechanism. The electrochemistry of AChE-generated thiocholine is studied at the mediator-modified electrodes in the presence and absence of ChO. It is observed that thiocholine undergoes both mediated and non-mediated oxidation in the absence of ChO as well as oxidation through enzyme-catalyzed mediated reactions. The results based on cyclic voltammetry on the oxidation of thiocholine at the surface of mediator-modified electrodes in the presence and absence of ChO are reported. In the presence of the ChO large anodic current is observed near the mediators redox potentials as compared to the anodic current in the absence of enzyme, which shows mediated bioelectrochemistry of thiocholine. The typical response curves for the detection of thiocholine/choline using mediators and ChO-modified electrodes below 0.24 V vs. Ag/AgCl in 0.1 M Tris–HCl buffer pH 8.0 are reported. Comparative analytical performance on the mediated electrochemical responses of the biosensors is discussed.

Chitosan encapsulated quantum dots platform for leukemia detection.

We report results of the studies relating to electrophoretic deposition of nanostructured composite of chitosan (CS)-cadmium-telluride quantum dots (CdTe-QDs) onto indium-tin-oxide coated glass substrate. The high resolution transmission electron microscopic studies of the nanocomposite reveal molecular level coating of the CdTe-QDs with CS molecules in the colloidal dispersion medium. This novel composite platform has been explored to fabricate an electrochemical DNA biosensor for detection of chronic myelogenous leukemia (CML) by immobilizing amine terminated oligonucleotide probe sequence containing 22 base pairs, identified from BCR-ABL fusion gene. The results of differential pulse voltammetry reveal that this nucleic acid sensor can detect as low as 2.56 pM concentration of complementary target DNA with a response time of 60s. Further, the response characteristics show that this fabricated bioelectrode has a shelf life of about 6 weeks and can be used for about 5-6 times. The results of experiments conducted using clinical patient samples reveal that this sensor can be used to distinguish CML positive and the negative control samples.

Nanopatterned Cadmium Selenide Langmuir–Blodgett Platform for Leukemia Detection

We present results of the studies relating to preparation of Langmuir-Blodgett (LB) monolayers of tri-n-octylphosphine oxide-capped cadmium selenide quantum dots (QCdSe) onto indium-tin oxide (ITO) coated glass substrate. The monolayer behavior has been studied at the air-water interface under various subphase conditions. This nanopatterned platform has been explored to fabricate an electrochemical DNA biosensor for detection of chronic myelogenous leukemia (CML) by covalently immobilizing the thiol-terminated oligonucleotide probe sequence via a displacement reaction. The results of electrochemical response studies reveal that this biosensor can detect target DNA in the range of 10(-6) to 10(-14) M within 120 s, has a shelf life of 2 months, and can be used about 8 times. Further, this nucleic acid sensor has been found to distinguish the CML-positive and the control negative clinical patient samples.

Studies on Ferrocene Immobilized Sol‐Gel Glasses and Its Application in the Construction of a Novel Solid‐State Ion Sensor

Two new sol-gel glass systems with immobilized ferrocene are developed using two different types of sol-gel precursors. System (1) is developed using ferrocene carboxaldehyde and a mixture of two silanes (3-aminopropyltriethoxy silane and 2-(3,4-epoxycyclohexyl)-ethyltrimethoxy silane). System (2) is developed using ferrocene monocarboxylic acid and a mixture of 3-glycidoxypropyltrimethoxysilane and trimethoxysilane. The surfaces of the sol-gel glasses are analyzed based on scanning electron microscopy (SEM). The electrochemistry of ferrocene in system 1 and system 2 is characterized based on cyclic voltammetry. System 1 shows capacitive CV at slow scan rate whereas system 2 shows good reversible electrochemistry of ferrocene. The potentiometric response of the ferrocene immobilized sol-gel glass (system 1) is studied in 10 mM Tris-HCl buffer pH 7.0. A reproducible potential difference of system 1 to the order of –30 mV is recorded for 2 months with respect to a double junction SCE reference electrode. An ion sensing membrane is assembled over the ferrocene immobilized sol-gel glass using plasticized PVC matrix membrane containing dibenzo-18-crown-6. A typical potentiometric response of the ion sensor is reported. The response of the ion-sensor shows better response time, high reproducibility and relatively better slope for potassium analysis as compared to earlier reported solid-state K+ ion-sensor based on dibenzo-18-crown-6 neutral carrier. The reproducibility, detection limit and relative response of the ion sensor to Na+ and NH4+ ions are reported.

Microstructured cystine dendrites-based impedimetric sensor for nucleic acid detection.

We report results of the studies relating to the fabrication and characterization of novel biosensing electrode by covalent immobilization of DNA onto microstructural cystine (Cys) prepared by acoustic cavitation method. The TEM investigations of these structures reveal transformation of microstructured Cys from nanorods to dendritic structure under optimum conditions. The Cys dendrites (denCys) have been investigated by XRD, FT-IR, and SEM studies. These biosensing electrodes have been fabricated by immobilization of Escherichia coli (E. coli)-specific DNA probe onto the dendritic cystine. The results of the electrochemical impedance spectroscopy studies reveal that this nucleic acid sensor exhibits linear response to cDNA in the concentration range of 10(-6) to 10(-14) M with response time of 30 min. The biosensing characteristics show that the fabricated E. coli sensor can be reused about 4 times and is stable for ∼4 weeks. The studies on cross-reactivity of the sensor for other water-borne pathogens like Salmonella typhimurium, Neisseria meningitides, and Klebsiella pneumonia reveal specificity of the bioelectrode for E. coli detection.

Nanostructuring of hierarchical 3D cystine flowers for high-performance electrochemical immunosensor

Here, we report a simple and reproducible method for large scale fabrication of novel flower and palm-leaf like 3D cystine microstructures (CMs) with high uniformity having a size of 50 µm and 10 µm respectively, through a facile aqueous solution route as a function of pH and concentration. In a proof-of-concept study, the 3D CMs have been further explored to fabricate a label-free high-performance electrochemical immunosensor by immobilizing monoclonal antibodies. Electrochemical methods were employed to study the stepwise modification of the system and the electronic transduction for the detection. The fabricated immunosensor design demonstrates high performance with enhanced sensitivity (4.70 cfu ml(-1)) and linear sensing range from 10 to 3 x 10(9) cfu ml(-1) a long shelf-life (35 days) and high selectivity over other bacterial pathogens. The enhanced performance originates from a novel nanostructuring in which the CMs provide higher surface coverage for the immobilization of antibodies providing excellent electronic/ionic conductivity which result in the enhanced sensitivity.

Electrochemical studies on D96N bacteriorhodopsin and its application in the development of photosensors

Abstract The electrochemical studies on D96N bacteriorhodopsin (BR) are reported based on chronoamperometry using immobilized BR on antimony–tin oxide (ATO) electrode. The absorption spectra of immobilized BR on ATO electrode shows an absorption peak at 570 nm suggesting the stability of immobilized BR on ATO. Chronoamperometry of the immobilized BR on ATO is studied using a one-compartment homemade electrochemical cell having the arrangement of device for external light exposure upon immobilized BR on ATO as working electrode, Ag/AgCl as reference electrode and a Pt foil as auxiliary electrode. The chronoamperometry is studied in the presence and absence of light following two approaches by controlling the duration of light exposure to immobilized BR: (i) exposure to external yellow light for 1 s and (ii) exposure to external light for 12–20 s. The variation of photocurrent with time under these conditions are reported and discussed. The approach (i) has been used for the analysis of amine and ammonium compounds by measuring photocurrents in peak height mode. A good correlation between peak photocurrent and the concentration of amine and ammonium compounds is recorded. The data on approach (ii) results in forward photocurrent in the presence of light and backward photocurrent when the light is shut off. The effects of lysine, arginine and ammonium nitrate on variations of forward and backward photocurrents are reported. The dependence of photocurrent on applied potential vs. Ag/AgCl is reported. The calibration curves for the analysis of ammonium ion and amine compounds based on the measurement of photocurrent are reported.

Electrochemical detection of a pathogenic Escherichia coli specific DNA sequence based on a graphene oxide–chitosan composite decorated with nickel ferrite nanoparticles

In this report, an electrochemical genosensor has been fabricated for Escherichia coli O157:H7 (E. coli) detection using a graphene oxide–nickel ferrite–chitosan (GO/NiF/ch) nanocomposite film as the sensing platform. The prepared GO/NiF/ch nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and thermo-gravimetric analysis. Nucleic acid hybridization technique was employed for the detection of a specific sequence of E. coli. The hybridization between the complementary DNA and probe DNA was investigated by differential pulse voltammetry (DPV) using methylene blue as redox indicator. The fabricated biosensor exhibits a linear response to complementary DNA in the concentration range of 10−6 to 10−16 M with a detection limit of 1 × 10−16 M.

Microfluidics Based Point-of-Care Diagnostics

Point‐of‐care (POC) diagnostic devices have been predicted to provide a boon in health care especially in the diagnosis and detection of diseases. POC devices have been found to have many advantages like a rapid and precise response, portability, low cost, and non‐requirement of specialized equipment. The major objective of a POC diagnostic research is to develop a chip‐based, self‐containing miniaturized device that can be used to examine different analytes in complex samples. Further, the integration of microfluidics (MF) with advanced biosensor technologies is likely to result in improved POC diagnostics. This paper presents the overview of the different materials (glass, silicon, polymer, paper) and techniques for the fabrication of MF based POC devices along with their wide range of biosensor applications. Besides this, the authors have presented in brief the challenges that MF is currently facing along with possible solutions that may result in the availability of the accessible, reliable, and cost‐efficient technology. The development of these devices requires the combination of developed MF components into POC devices that are user‐friendly, sensitive, stable, accurate, low cost, and minimally invasive. These MF based POC devices have tremendous potential in providing improved healthcare including easy monitoring, early detection of disease, and increased personalization.

Quantum dot-based microfluidic biosensor for cancer detection

We report results of the studies relating to fabrication of an impedimetric microfluidic–based nucleic acid sensor for quantification of DNA sequences specific to chronic myelogenous leukemia (CML). The sensor chip is prepared by patterning an indium–tin–oxide (ITO) coated glass substrate via wet chemical etching method followed by sealing with polydimethylsiloxane (PDMS) microchannel for fluid control. The fabricated microfluidic chip comprising of a patterned ITO substrate is modified by depositing cadmium selenide quantum dots (QCdSe) via Langmuir–Blodgett technique. Further, the QCdSe surface has been functionalized with specific DNA probe for CML detection. The probe DNA functionalized QCdSe integrated miniaturized system has been used to monitor target complementary DNA concentration by measuring the interfacial charge transfer resistance via hybridization. The presence of complementary DNA in buffer solution significantly results in decreased electro-conductivity of the interface due to presence of...