Rahul Singhal

Immobilization of lactate dehydrogenase on electrochemically prepared polypyrrole–polyvinylsulphonate composite films for application to lactate biosensors

Abstract The immobilization of lactate dehydrogenase (LDH) on electrochemically polymerized polypyrrole–polyvinylsulphonate (PPY–PVS) films has been accomplished via cross-linking technique using glutaraldehyde. The characterization of the LDH-immobilized PPY–PVS films has been carried out using FTIR and cyclic voltammetry. These PPY–PVS–LDH electrodes are shown to have a detection limit of 1×10 −4 M, a response time of about 40 s, and a shelf-life of about 2 weeks and these can be used for l -lactate estimation from 0.5 to 6 mM.

Immobilization of urease on poly(N-vinyl carbazole)/stearic acid Langmuir–Blodgett films for application to urea biosensor

Urease was immobilized in mixed monolayers of poly(N-vinyl carbazole) (PNVK) and stearic acid (SA) formed at an air-water interface. The monolayers were transferred onto indium-tin-oxide (ITO) coated glass plates using Langmuir-Blodgett (LB) film deposition technique. Urease immobilized on PNVK/SA LB films, characterized using FTIR and UV-visible spectroscopy, was found to exhibit increased stability over a wide pH (6.5-8.5) and temperature (25-50 degrees C) range. Potentiometric measurements on these urease electrodes were carried out using an ammonium ion analyzer. Two values for K(m)(app) were obtained at lower and higher concentrations of substrate urea.

Langmuir–Blodgett films of poly(3-dodecyl thiophene) for application to glucose biosensor

Abstract Monolayers of poly(3-dodecyl thiophene) (P3DT) have been obtained on indium–tin-oxide (ITO) coated glass plates by dispensing mixed solution of P3DT and stearic acid (SA) prepared in chloroform onto water subphase by a microsyringe. The pressure–area isotherms of these P3DT–SA monolayers were studied as a function of temperature and pH. The monolayer stability onto the water subphase has been experimentally studied at different temperatures, pH and surface pressure. These P3DT–SA monolayers fabricated onto the ITO-coated glass plates were characterized using FTIR and cyclic voltammetry studies. The desired enzyme monolayers were fabricated by dispensing glucose oxidase mixed with P3DT/SA in chloroform and were transferred onto desired ITO-coated glass. An attempt has been made to utilize these P3DT/SA/GOX LB films for fabrication of a glucose biosensor.

One-dimensional nanostructures: fabrication, characterisation and applications

Abstract This review presents the advancement in synthesis and characterisation techniques of one-dimensional nanostructures (ODNS) as well as their potential for novel applications. In the first section of the review, the authors describe the synthesis techniques of one-dimensional nanostructures, i.e. template based synthesis, vapour phase growth, solution based growth and other innovative techniques. Various characterisation techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are described in detail, followed by a comprehensive review of the unique material properties of one-dimensional nanostructures. The final section of this paper presents current state of the art chemical and biological sensing applications as well as other potential technologies which may emerge due to the advantage nanomaterials have over their bulk counterparts.

Immobilization of glucose oxidase onto Langmuir–Blodgett films of poly-3-hexylthiophene

Abstract Monolayers of poly(3-hexyl thiophene) (P3HT) were obtained by dispensing a solution of P3HT with stearic acid (SA) in chloroform at air-water interface using Joyce–Loebl LB trough. These films were transferred onto indium-tin-oxide coated glass plate by vertical dipping method. Enzyme glucose oxidase (GOX) was immobilized on the films using LB technique. These films were characterized by X-ray diffraction and atomic force microscopic techniques. Photometric response of these P3HT/SA/GOX films was obtained as a function of glucose concentration. These P3HT/SA/GOX LB films show a linearity from 100 to 500 mg/dl of glucose concentration.

Conducting polymer based biomolecular electronic devices

Biomolecular electronics is rapidly evolving from physics, chemistry, biology, electronics and information technology. Organic materials such as proteins, pigments and conducting polymers have been considered as alternatives for carrying out the functions that are presently being performed by semiconductor silicon. Conducting polymers such as polypyrroles, polythiophenes and polyanilines have been projected for applications for a wide range of biomolecular electronic devices such as optical, electronic, drug-delivery, memory and biosensing devices. Our group has been actively working towards the application of conducting polymers to Schottky diodes, metal-insulator-semiconductor (MIS) devices and biosensors for the past 10 years. This paper is a review of some of the results obtained at our laboratory in the area of conducting polymer biomolecular electronics.

Synthesis and characterization of fluoro-substituted polyaniline

Poly(2-fluoroaniline) was prepared by both chemical and electrochemical polymerization in acidic medium. Characterization of poly(2-fluoroaniline) was accomplished experimentally using ultraviolet-visible, Fourier transform infrared, differential scanning calorimetry, thermal gravimetric analysis, and X-ray diffraction techniques, respectively. Scanning electron microscopy studies revealed globular morphology of chemically synthesized poly(2-fluoroaniline). The cyclic voltammetric studies revealed diffusion-controlled phenomenon in electrochemically synthesized poly(2-fluoroaniline).

Time-of-Flight Photocarrier Mobility in Langmuir-Blodgett Films of Regioregular Poly(3-hexylthiophene).

Time-of-flight (TOF) measurements are conducted in annealed (50°C) Langmuir-Blodgett (LB) films of chemically prepared regioregular 33.5% undoped poly(3-hexylthiophene) (P3HT) mixed with 66.5% stearic acid. The characterization of these poly(3-hexylthiophene)-stearic acid (P3HT-SA) films is accomplished using scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-visible analyses. The value of the TOF photocarrier mobility obtained in P3HT-SA LB film sandwiched between metal (Al) and indium-tin-oxide (ITO) glass is experimentally determined as 1.8×10-5 cm2/Vs at an applied field of 1.3×106 V/cm.

Preparation and characterization of poly-N-vinyl carbazole Langmuir-Blodgett films.

Langmuir monolayers of poly-N-vinyl carbazole (PNVK) were obtained by dispensing PNVK dissolved in tetrahydrofuran onto an air-water interface. Surface pressure-area isotherms of mixed monolayer of the PNVK were studied under different subphase conditions such as temperature and pH of the subphase. It was demonstrated that the monolayer of PNVK remained stable over a temperature range of 10–40°C. The area per molecule of the solid phase was found to be 31Å2. These monolayers were transferred onto indium-tin-oxide-coated glass plates and characterized by spectroscopic and electrochemical techniques.