Ida Tiwari

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.

Studies on Glucose Biosensors Based on Nonmediated and Mediated Electrochemical Oxidation of Reduced Glucose Oxidase Encapsulated Within Organically Modified Sol-Gel Glasses

A new, organically modified sol-gel glass electrode is reported using 3-aminopropyltriethoxy silane and 2-(3,4-epoxycyclohexyl)-ethyltrimethoxy silane as sol-gel precursors for the construction of electrochemical biosensors. Four different systems of new sol-gel glass modified glucose electrodes are made in acidic medium having common sol-gel precursors and: 1) glucose oxidase, 2) glucose oxidase along with polyethylene glycol, 3) glucose oxidase and graphite powder, and 4) glucose oxidase along with polyethylene glycol and graphite powder. Both nonmediated and mediated electrochemical regeneration of immobilized glucose oxidase within sol-gel glasses are studied in these four systems. The nonmediated regeneration is achieved in the presence of oxygen as electron donor whereas mediated regeneration involves soluble ferrocene monocarboxylic acid as electron donor in each system. The electrochemical performance of sol-gel glass based biosensors is compared on the basis of cyclic voltammetry and amperometry. This leads to the observations: i) all four systems reach a diffusion limited condition associated with the transport of soluble ferrocene monocarboxylic acid as well as for dissolved oxygen within the sol-gel matrix, ii) the relative rate of diffusion of these analytes increases from system 1 to system 4, iii) both nonmediated and mediated amperometric responses at suitable potentials are based on the oxidation of H2O2 and enzymatically reduced soluble ferrocene with relatively amplified electrochemical signal of system 4. Data on the reduction of oxygen at conventional graphite disk electrode and at typical sol-gel glass modified electrode are reported.

Studies on polycarbazole‐modified electrode and its applications in the development of solid‐state potassium and copper(II) ion sensors

Electrochemical synthesis of polycarbazole, having better stability and electrochromic activity, in dichloromethane containing 0.1 M tetrabutyl ammonium perchlorate (TBAP) is reported at 1.4 V versus Ag/AgCl. The electrochemistry based on cyclic voltammetric measurements in dichloromethane containing TBAP show redox behavior of the polymer associated to doping and de-doping of ClO ion within the polymer interstices. The polycarbazole matrix obtained by the potentiostatic and potentiodynamic modes of electropolymerization is characterized based on scanning electron microscopy, differential calorimetry, and infrared spectroscopy. De-doping of the polymer is studied by electrochemical reduction in TBAP-free dichloromethane followed by incubation of the polymer film in 1 M aqueous KCl solution for 24 h. The open circuit potential (OCP) of doped and de-doped polycarbazole modified electrode under the present experimental conditions is found to 462 and 19 mV, respectively, versus SCE in 0.1 M NH4NO3. The de-doped polymer shows remarkable sensitivity and selective to Cu(II) ion compared to its sensitivity for Fe3+, Ni2+, Co2+, Pb2+, and Cu+ ions. A typical response of the de-doped polymer electrode to Cu(II) ion is reported. On the other hand, ClO doped polymer is used in the development of solid-state K+ ion sensors using dibenzo-18-crown-6/valinomycin as a neutral carrier–based, plasticized poly vinyl chloride matrix membrane assembled over a polymer-modified electrode. The doped polymer under this condition helps in maintaining charge stabilization across Pt/polymer and polymer/PVC interfaces. The lowest detection limit for the potassium ion sensor is 5 × 10−5M with a slope of 58 mV/decade for valinomycin-based sensor and 6.8 × 10−5M with a slope of 54 mV for dibenzo-18-crown-6 carriers with a wide linearity. The typical potentiometric results on the sensitivity, detection limits, and OCP to K+ ion recorded using present polymer are compared with the data recorded earlier using polyindole and a similar neutral carrier–based PVC membrane. A comparison on electrode kinetics of these two polymer-modified electrodes also has been made using the data on Tafel plots to study the relative kinetic polarizability based on ion-exchange currents.

Polyaniline/polyacrylic acid/ multi-walled carbon nanotube modified electrodes for sensing ascorbic acid

A multi-walled carbon nanotube composite electrode incorporating Polyaniline (PANI) and Polyacrylic acid (PAA) is presented by diffusing aniline and PAA into Nafion- MWCNTs membranes supported upon a platinum macrodisc electrode. Nafion is found to be an ideal medium for dispersion of MWCNTs and for the formation of a homogeneous composite. The composite has been characterized utilizing SEM, TEM, FT-IR and electrochemical techniques. Electrochemical characterization reveals that the redox activity of the composite is improved with the cumulative effect of MWCNTs and PAA as additives. The electroanalytical behavior of the composite is evaluated towards the sensing of ascorbic acid in the presence of dopamine and uric acid exhibiting a detection limit of 2.5 × 10−7 M.

A Novel Ferrocene-Encapsulated Palladium-Linked Ormosil-Based Electrocatalytic Biosensor. The Role of the Reactive Functional Group

A novel palladium-linked ormosil material with encapsulated ferrocene is reported along with its application in bioelectrocatalysis. The Pd-glycidoxypropyltrimethoxysilane is made by mixing an aqueous solution of palladium chloride and glycidoxypropyltrimethoxysilane. The linkage of palladium with glycidoxypropyltrimethoxysilane is confirmed by UV-vis, mass, and 13C spectroscopy. It is suggested that Pd is sandwiched between two molecules of glycidoxypropyltrimethoxysilane replacing oxygen. The new ormosil is made using Pd-linked silane precursor containing ferrocene monocarboxylic acid, trimethoxysilane and HCl. The formation of ormosil at two different temperatures (10 and 30 °C) is also studied, with the result that the ormosil formed at 10 °C does not show electrocatalysis of glucose oxidase whereas the ormosil made at 30 °C is found to be an efficient bioelectrocatalyst. The cyclic voltammetry results show peak separation of 57–59 mV of encapsulated ferrocene made at 30 °C and relatively large peak separation of the one made at 10 °C. The performance, stability, and reproducibility of the new ormosil based glucose biosensor are discussed. Another important investigation in support of the above outcome is reported showing the self-assembly of palladium on the reactive solid state ormosil surface. The reactive ormosil is developed using a mixture of trimethoxysilane and 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane in acidic medium.

An insight review on the application of polymer-carbon nanotubes based composite material in sensor technology

Carbon nanotubes (CNT) polymer composites have shown potential applications for sensor/biosensor fabrication. Methods for preparation, characteristics are highlighted and future aspects are explored. Various analytes and polymeric materials have been cited to prove the importance of polymer/CNT composite systems in sensor technology.

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.

A Novel Amperometric Hydrogen Peroxide Biosensor Based on Horseradish Peroxidase Incorporated in Organically Modified Sol-Gel Glass Matrix/Graphite Paste with Multiwalled Carbon Nanotubes

We herein report an electrochemical hydrogen peroxide sensor based on horseradish peroxidase immobilized in organically modified sol-gel glass (ormosil) with mediator ferricyanide along with multiwalled carbon nanotubes (mwcnts). The ormosil material is converted to fine powder followed by incorporation within graphite paste electrode. The electrochemistry of redox materials encapsulated within ormosil has been studied. The requirement of mwcnts is examined. The ormosil prepared with optimum concentration of mwcnts shows better redox electrochemistry as compared to that made without mwcnts. The biosensor has been characterized by cyclic voltammetry and chroanoamperometry. The performance, stability, and reproducibility of a new peroxide biosensor 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.

Design of screen-printed bulk modified electrodes using anthraquinone–cysteamine functionalized gold nanoparticles and their application to the detection of dissolved oxygen

We investigated the electroanalytical determination of dissolved oxygen using low-cost disposable screen-printed bulk modified electrodes based on nanostructures. A nanostructure based on gold nanoparticles functionalized with an anthraquinone derivative and cysteamine was prepared. The nanostructured material was characterized morphologically using transmission electron microscopy and further physical characterization was carried out by energy-dispersive X-ray spectrometry. The prepared material was incorporated into a screen-printable graphite ink to develop the technology for the economic mass production of the next generation of field sensors. The electroanalytical determination of dissolved oxygen was possible in the range 0.2–6.1 mg L−1 with a detection limit of 0.131 mg L−1 (based on 3σ). We demonstrate proof-of-concept that this approach provides a rapid and inexpensive sensing strategy for the determination of dissolved oxygen in contaminated water samples.