Padmanabhan Santhosh

Electrochemical determination of dopamine and ascorbic acid at a novel gold nanoparticles distributed poly(4-aminothiophenol) modified electrode

A modified electrode is fabricated by embedding gold nanoparticles into a layer of electroactive polymer, poly(4-aminothiophenol) (PAT) on the surface of glassy carbon (GC) electrode. Cyclic voltammetry (CV) is performed to deposit PAT and concomitantly deposit Au nanoparticles. Field emission transmission electron microscopic image of the modified electrode, PAT-Au(nano)-ME, indicates the presence of uniformly distributed Au nanoparticles having the sizes of 8-10nm. Electrochemical behavior of the PAT-Au(nano)-ME towards detection of ascorbic acid (AA) and dopamine (DA) is studied using CV. Electrocatalytic determination of DA in the presence of fixed concentration of AA and vice versa, are studied using differential pulse voltammetry (DPV). PAT-Au(nano)-ME exhibits two well defined anodic peaks at the potential of 75 and 400mV for the oxidation of AA and DA, respectively with a potential difference of 325mV. Further, the simultaneous determination of AA and DA is studied by varying the concentration of AA and DA. PAT-Au(nano)-ME exhibits selectivity and sensitivity for the simultaneous determination of AA and DA without fouling by the oxidation products of AA or DA. PAT and Au nanoparticles provide synergic influence on the accurate electrochemical determination of AA or DA from a mixture having any one of the component (AA or DA) in excess. The practical analytical utilities of the PAT-Au(nano)-ME are demonstrated by the determination of DA and AA in dopamine hydrochloride injection and human blood serum samples.

Electrocatalytic oxidation of NADH at gold nanoparticles loaded poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) film modified electrode and integration of alcohol dehydrogenase for alcohol sensing.

A new modified electrode is fabricated by dispersing gold nanoparticles onto the matrix of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid), PEDOT-PSS. The electrocatalytic activity of the PEDOT-PSS-Au(nano) electrode towards the oxidation of beta-nicotinamide adenine dinucleotide (NADH) is investigated. A substantial decrease in the overpotential (>0.7 V) has been observed for the oxidation of NADH at the PEDOT-PSS-Au(nano) electrode in comparison to the potential at PEDOT-PSS electrode. The Au nanoparticles dispersed in the PEDOT-PSS matrix prevents the fouling of electrode surface by the oxidation products of NADH and augments the oxidation of NADH at a less positive potential (+0.04V vs. SCE). The electrode shows high sensitivity to the electrocatalytic oxidation of NADH. Further, the presence of ascorbic acid and uric acid does not interfere during the detection of NADH. Important practical advantages such as stability of the electrode (retains approximately 95% of its original activity after 20 days), reproducibility of the measurements (R.S.D.: 2.8%; n=5), selectivity and wide linear dynamic range (1-80 microM; R(2)=0.996) are achieved at PEDOT-PSS-Au(nano) electrode. The ability of PEDOT-PSS-Au(nano) electrode to promote the electron transfer between NADH and the electrode makes us to fabricate a biocompatible dehydrogenase-based biosensor for the measurement of ethanol. The biosensor showed high sensitivity to ethanol with rapid detection, good reproducibility and excellent stability.

Fabrication of enzymatic glucose biosensor based on palladium nanoparticles dispersed onto poly(3,4-ethylenedioxythiophene) nanofibers.

A new methodology involving the combination of a soft template (surfactant) and an ionic liquid (co-surfactant) is used to electrodeposit poly(3,4-ethylenedioxythiophene) (PEDOT) nanofibers. Electrochemical deposition of palladium nanoparticles and glucose oxidase (GOx) immobilization are done sequentially into nanofibrous PEDOT to fabricate the modified electrode (ME) (denoted as PEDOT-Pd/GOx-ME). The PEDOT-Pd/GOx-ME displays excellent performances for glucose at +0.4 V (vs. Ag/AgCl) with a high sensitivity (1.6 mA M(-)(1) cm(-2)) in a wider linear concentration range, 0.5 to 30 mM (correlation coefficient of 0.9985). Further, the electrode is insusceptible to the electroactive interfering species.

Enzyme logic gates for the digital analysis of physiological level upon injury.

A biocomputing system composed of a combination of AND/IDENTITY logic gates based on the concerted operation of three enzymes: lactate oxidase, horseradish peroxidase and glucose dehydrogenase was designed to process biochemical information related to pathophysiological conditions originating from various injuries. Three biochemical markers: lactate, norepinephrine and glucose were applied as input signals to activate the enzyme logic system. Physiologically normal concentrations of the markers were selected as logic 0 values of the input signals, while their abnormally increased concentrations, indicative of various injury conditions were defined as logic 1 input. Biochemical processing of different patterns of the biomarkers resulted in the formation of norepiquinone and NADH defined as the output signals. Optical and electrochemical means were used to follow the formation of the output signals for eight different combinations of three input signals. The enzymatically processed biochemical information presented in the form of a logic truth table allowed distinguishing the difference between normal physiological conditions, pathophysiological conditions corresponding to traumatic brain injury and hemorrhagic shock, and abnormal situations (not corresponding to injury). The developed system represents a biocomputing logic system applied for the analysis of biomedical conditions related to various injuries. We anticipate that such biochemical logic gates will facilitate decision-making in connection to an integrated therapeutic feedback-loop system and hence will revolutionize the monitoring and treatment of injured civilians and soldiers.

Hybrid Polymer-Grafted Multiwalled Carbon Nanotubes for In vitro Gene Delivery

Carbon nanotubes (CNTs) consist of carbon atoms arranged in sheets of graphene rolled up into cylindrical shapes. This class of nanomaterials has attracted attention because of their extraordinary properties, such as high electrical and thermal conductivity. In addition, development in CNT functionalization chemistry has led to an enhanced dispersibility in aqueous physiological media which indeed broadens the spectrum for their potential biological applications including gene delivery. The aim of this study is to determine the capability of different cationic polymer-grafted multiwalled carbon nanotubes (MWNTs) (polymer-g-MWNTs) to efficiently complex and transfer plasmid DNA (pCMV-βGal) in vitro without promoting cytotoxicity. Carboxylated MWNT is chemically conjugated to the cationic polymers polyethylenimine (PEI), polyallylamine (PAA), or a mixture of the two polymers. In order to explore the potential of these polymer-g-MWNTs as gene delivery systems, we first study their capacity to complex plasmid DNA (pDNA) using agarose gel electrophoresis. Gel migration studies confirm pDNA binding to polymer-g-MWNT with different affinities, highest for PEI-g-MWNT and PEI/PAA-g-CNT constructs. β-galactosidase expression is assessed in human lung epithelial (A549) cells, and the cytotoxicity is determined by modified LDH assay after 24 h incubation period. Additionally, PEI-g-MWNT and/or PEI/PAA-g-MWNT reveal an improvement in gene expression when compared to the naked pDNA or to the equivalent amounts of PEI polymer alone. Mechanistically, pDNA was delivered by the polymer-g-MWNT constructs via a different pathway compared to those used by polyplexes. In conclusion, polymer-g-MWNTs may be considered in the future as a versatile tool for efficient gene transfer in cancer cells in vitro, provided their toxicological profile is established.

Microneedle array-based carbon paste amperometric sensors and biosensors

The design and characterization of a microneedle array-based carbon paste electrode towards minimally invasive electrochemical sensing are described. Arrays consisting of 3 × 3 pyramidal microneedle structures, each with an opening of 425 µm, were loaded with a metallized carbon paste transducer. The renewable nature of carbon paste electrodes enables the convenient packing of hollow non-planar microneedles with pastes that contain assorted catalysts and biocatalysts. Smoothing the surface results in good microelectrode-to-microelectrode uniformity. Optical and scanning electron micrographs shed useful insights into the surface morphology at the microneedle apertures. The attractive performance of the novel microneedle electrode arrays is illustrated in vitro for the low-potential detection of hydrogen peroxide at rhodium-dispersed carbon paste microneedles and for lactate biosensing by the inclusion of lactate oxidase in the metallized carbon paste matrix. Highly repeatable sensing is observed following consecutive cycles of packing/unpacking the carbon paste. The operational stability of the array is demonstrated as well as the interference-free detection of lactate in the presence of physiologically relevant levels of ascorbic acid, uric acid, and acetaminophen. Upon addressing the biofouling effects associated with on-body sensing, the microneedle carbon paste platform would be attractive for the subcutaneous electrochemical monitoring of a number of physiologically relevant analytes.

Voltammetric determination of nitroaromatic and nitramine explosives contamination in soil

The contamination of soil by nitroaromatic and nitramine explosives is widespread during the manufacture, testing and disposal of explosives and ammunitions. The analysis for the presence of trace explosive contaminants in soil becomes important in the light of their effect on the growth of different varieties of plants and crops. 2,4,6-Trinitrotoluene (TNT), cyclotrimethylene trinitramine (Research Department explosive, RDX) and cyclotetramethylene tetranitramine (high melting point explosive, HMX), other related explosive compounds and their by-products must be monitored in soil and surrounding waterways since these are mutagenic, toxic and persistent pollutants that can leach from the contaminated soil to accumulate in the food chain. In this study, a voltammetric method has been developed for the determination of explosive such as RDX, HMX and TNT. The electrochemical redox behavior of RDX, HMX and TNT was studied through cyclic voltammetry and quantitative determination was carried out by using square wave voltammetry technique. Calibration curves were drawn and were linear in the range of 63-129ppm for RDX with a detection limit of 10ppm, 49-182ppm for HMX with a detection limit of 1ppm and 38-139ppm for TNT with a detection limit of 1ppm. This method was applied to determine the contaminations in several soil samples that yielded a relative error of 1% in the concentrations.

Enzymatic AND Logic Gates Operated Under Conditions Characteristic of Biomedical Applications

Experimental and theoretical analyses of the lactate dehydrogenase and glutathione reductase based enzymatic AND logic gates in which the enzymes and their substrates serve as logic inputs are performed. These two systems are examples of the novel, previously unexplored class of biochemical logic gates that illustrate potential biomedical applications of biochemical logic. They are characterized by input concentrations at logic 0 and 1 states corresponding to normal and pathophysiological conditions. Our analysis shows that the logic gates under investigation have similar noise characteristics. Both significantly amplify random noise present in inputs; however, we establish that for realistic widths of the input noise distributions, it is still possible to differentiate between the logic 0 and 1 states of the output. This indicates that reliable detection of pathophysiological conditions is indeed possible with such enzyme logic systems.

One-pot construction of mediatorless bi-enzymatic glucose biosensor based on organic-inorganic hybrid

A new methodology for the fabrication of bienzymatic amperometric glucose biosensor based on the use of an organic-inorganic hybrid is presented. The fabrication involves a self-assembly directed one-pot electrochemical process. Bi-enzymes, horseradish peroxidase (HRP) and glucose oxidase (GOx) are immobilized into the porous and electroactive silica-polyaniline hybrid composite through electrochemical polymerization of N[3-(trimethoxysilyl)propyl]aniline in the presence of enzymes. The modified electrode is designated as PTMSPA/HRP-GOx. The direct electron transfer of HRP is achieved at the modified electrode. Also, the electrode exhibits excellent bio-electro-catalytic activity for the reduction of hydrogen peroxide. The response current at PTMSPA/HRP-GOx modified electrode revealed a good linear relationship with concentration of glucose range between 1 and 20mM with a response time of 7s. Thus, the modified electrode shows the combined advantages of polyaniline and silica networks through synergistic influence from the individual components. The PTMSPA assembly has shown the potential for a third generation amperometric biosensor.

Electrochemical detection of celecoxib at a polyaniline grafted multiwall carbon nanotubes modified electrode

A modified electrode is fabricated by grafting polyaniline (PANI) chains onto multiwall carbon nanotubes (MWNTs) and utilized for the adsorptive reduction of celecoxib (CEL). PANI-g-MWNTs modified electrode appreciably enhances the sensitive detection of CEL in extremely lower concentrations (1x10(-11)M). Square wave stripping voltammogram (SWSV) shows a reduction peak at -1.08V with a high peak current for SW frequency of 100Hz, amplitude of 25mV and step height of 6mV. The high surface area of PANI-g-MWNTs is effectively utilized for the adsorption of CEL to preconcentrate at the electrode. The PANI chains covalently linked to MWNTs mediate the electron transfer processes. The present finding open-up the scope for extending on the use of other conducting polymers grafted MWNTs modified electrodes for the detection of compounds that do not have surface-active properties at conventional electrodes.