B. D. Malhotra

Application of conducting polymers to biosensors

Recently, conducting polymers have attracted much interest in the development of biosensors. The electrically conducting polymers are known to possess numerous features, which allow them to act as excellent materials for immobilization of biomolecules and rapid electron transfer for the fabrication of efficient biosensors. In the present review an attempt has been made to describe the salient features of conducting polymers and their wide applications in health care, food industries, environmental monitoring etc.

Iron oxide nanoparticles–chitosan composite based glucose biosensor

Iron oxide (Fe(3)O(4)) nanoparticles prepared using co-precipitation method have been dispersed in chitosan (CH) solution to fabricate nanocomposite film on indium-tin oxide (ITO) glass plate. Glucose oxidase (GOx) has been immobilized onto this CH-Fe(3)O(4) nanocomposite film via physical adsorption. The size of the Fe(3)O(4) nanoparticles estimated using X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) has been found to be approximately 22 nm. The CH-Fe(3)O(4) nanocomposite film and GOx/CH-Fe(3)O(4)/ITO bioelectrode have been characterized using UV-visible and Fourier transform infrared (FTIR) spectroscopic and scanning electron microscopy (SEM) techniques, respectively. This GOx/CH-Fe(3)O(4)/ITO nanocomposite bioelectrode has response time of 5s, linearity as 10-400 mgdL(-1) of glucose, sensitivity as 9.3 microA/(mgdLcm(2)) and shelf life of about 8 weeks under refrigerated conditions. The value of Michaelis-Menten (K(m)) constant obtained as 0.141 mM indicates high affinity of immobilized GOx towards the substrate (glucose).

Recent advances in polyaniline based biosensors.

The present paper contains a detailed overview of recent advances relating to polyaniline (PANI) as a transducer material for biosensor applications. This conducting polymer provides enormous opportunities for binding biomolecules, tuning their bio-catalytic properties, rapid electron transfer and direct communication to produce a range of analytical signals and new analytical applications. Merging the specific nature of different biomolecules (enzymes, nucleic acids, antibodies, etc.) and the key properties of this modern conducting matrix, possible biosensor designs and their biosensing characteristics have been discussed. Efforts have been made to discuss and explore various characteristics of PANI responsible for direct electron transfer leading towards fabrication of mediator-less biosensors.

Prospects of conducting polymers in molecular electronics

Molecular electronics (ME) is rapidly evolving from physics, chemistry, biology, electronics and information technology. This is because the present-day advanced silicon chip can store about 16 million bytes of information within an area less than 1 cm2. Organic materials such as proteins, pigments and conducting polymers (CPs) have been considered as alternatives for carrying out the same functions that are presently being performed by semiconductor silicon. Among these, CPs have demanded the maximum attention. These ME materials differ from conventional polymers by having a delocalized electronic structure that can accommodate charge carriers such as electrons and holes. Besides, these conjugated electronic materials exhibit Peierl’s instabilities due to built-in highly anisotropic interactions. It has been proposed that electrical conduction in CPs occurs via non-linear (or topological) defects (solitons/polarons) generated either during polymerization or as a consequence of doping. Solitons and polarons have recently been shown to have implications in the technical development of ME devices. CPs such as polypyrroles, polythiophenes and polyanilines have been projected for applications for a wide range of ME devices. One of the main reasons for such a wide-spread interest is due to the reported observation that these interesting electronic materials exhibit full range of properties from insulator to superconductor depending upon chemical modification. CPs have been found to have applications as optical, electronic, drug-delivery, memory and biosensing devices. The major challenge confronting the material scientists including chemists and physicists is how do the properties of these electronic materials differ from those of conventional semiconductors. Another advantage lies in the fact that these materials possess specific advantages such as high packing density, possibility of controlling shape and electronic properties by chemical modification. Our group has been actively working towards the application of CPs to Schottky diodes, metal–insulator–semiconductor devices and biosensors for the past about 10 years. This paper is a review of some of the results obtained at our laboratory in the area of CP ME.

Cholesterol biosensor based on rf sputtered zinc oxide nanoporous thin film

Cholesterol oxidase (ChOx) has been immobilized onto zinc oxide (ZnO) nanoporous thin films grown on gold surface. A preferred c-axis oriented ZnO thin film with porous surface morphology has been fabricated by rf sputtering under high pressure. Optical studies and cyclic voltammetric measurements show that the ChOx∕ZnO∕Au bioelectrode is sensitive to the detection of cholesterol in 25–400mg∕dl range. A relatively low value of enzyme’s kinetic parameter (Michaelis-Menten constant) ∼2.1mM indicates enhanced enzyme affinity of ChOx to cholesterol. The observed results show promising application of nanoporous ZnO thin film for biosensing application without any functionalization.

Biosensors for clinical diagnostics industry

There is an urgent need in the medical diagnostics laboratories for accurate, fast and inexpensive devices, which can be routinely used. The reliable and accurate information on the desired biochemical parameters is an essential prerequisite for effective healthcare. In this context, biosensors are considered to provide viable solutions to the problems posed by the contemporary healthcare industry. This is because these biosensing devices offer considerable advantages, such as specificity, small size faster response and cost. It is anticipated that these bioanalytical tools can be used for frequent measurements of metabolites, blood cations and gases, etc. In this paper, an attempt has been made to highlight some of the trends that rule the research and developments of some of the important biosensors that are likely to accelerate the growth of clinical diagnostics industry.

Zinc oxide nanoparticles-chitosan composite film for cholesterol biosensor.

Zinc oxide nanoparticles (NanoZnO) uniformly dispersed in chitosan (CHIT) have been used to fabricate a hybrid nanocomposite film onto indium-tin-oxide (ITO) glass plate. Cholesterol oxidase (ChOx) has been immobilized onto this NanoZnO-CHIT composite film using physiosorption technique. Both NanoZnO-CHIT/ITO electrode and ChOx/NanoZnO-CHIT/ITO bioelectrode have been characterized using Fourier transform-infrared (FTIR), X-ray diffraction (XRD), cyclic voltammetry (CV), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) techniques, respectively. The ChOx/NanoZnO-CHIT/ITO bioelectrode exhibits linearity from 5 to 300 mg dl(-1) of cholesterol with detection limit as 5 mg dl(-1), sensitivity as 1.41x10(-4) A mg dl(-1) and the value of Michaelis-Menten constant (K(m)) as 8.63 mg dl(-1). This cholesterol biosensor can be used to estimate cholesterol in serum samples.

Recent advances in self-assembled monolayers based biomolecular electronic devices

Self-assembled monolayers (SAMs) have aroused much interest due to their potential applications in biosensors, biomolecular electronics and nanotechnology. This has been largely attributed to their inherent ordered arrangement and controllable properties. SAMs can be formed by chemisorption of organic molecules containing groups like thiols, disulphides, amines, acids or silanes, on desired surfaces and can be used to fabricate biomolecular electronic devices. We focus on recent applications of organosulphur compounds (thiols) based SAMs to biomolecular electronic devices in the last about 3 years.

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.

Organic–Inorganic Hybrid Nanocomposite-Based Gas Sensors for Environmental Monitoring

Environmental Monitoring Ajeet Kaushik,*,†,‡ Rajesh Kumar,*,‡,§ Sunil K. Arya, Madhavan Nair,† B. D. Malhotra, and Shekhar Bhansali‡ †Center for Personalized Nanomedicine, Institute of Neuroimmune Pharmacology, Department of Immunology, Herbert Wertheim College of Medicine, Florida International University, Miami, Florida 33199, United States ‡Bio-MEMS Microsystems Laboratory, Department of Electrical and Computer Engineering, College of Engineering, Florida International University, Miami, Florida 33174, United States Department of Physics, Panjab University, Chandigarh 160014, India Bioelectronics Program, Institute of Microelectronics, A*Star, 11 Science Park Road, Singapore Science Park II, Singapore Department of Biotechnology, Delhi Technological University, Shahbad Daulatpur, Delhi 110042, India