Recent trends in electrochemical biosensors of superoxide dismutases.

Superoxide dismutases (SODs), a family of ubiquitous enzymes, provide essential protection to biological systems against uncontrolled reactions with oxygen- and nitrogen- based radical species. We review first the role of SODs in oxidative stress and the other biological functions such as peroxidase, nitrite oxidase, thiol oxidase activities etc., implicating its role in neurodegenerative, cardiovascular diseases, and ageing. Also, this review focuses on the development of electrochemical label-free immunosensor for SOD1 and the recent advances in biosensing assay methods based on their catalytic and biological functions with various substrates including reactive oxygen species (superoxide anion radical, hydrogen peroxide), nitric oxide metabolites (nitrite, nitrate) and thiols using thiol oxidase activity. Furthermore, we emphasize the progress made in improving the detection performance through incorporation of the SOD into conducting polymers and nanocomposite matrices. In addition, we address the potential opportunities, challenges, advances in electrochemical-sensing platforms and development of portable analyzer for point-of-care applications.

Electrochemical incorporation of hemin in a ZnO-PPy nanocomposite on a Pt electrode as NO(x) sensor.

An electrochemical NO(x) sensor was fabricated based on the incorporation of hemin on a ZnO-PPy nanocomposite modified Pt electrode. Scanning electron microscopy, energy dispersive X-ray analysis and cyclic voltammetry were used to confirm the successful stepwise assembly procedure for the sensor. The electrocatalytical behavior of the sensor was investigated by cyclic voltammetry. The hemin-ZnO-PPy-Pt electrode exhibited characteristic hemin reversible redox peaks at 0.035 V and -0.11 V vs. Ag/AgCl respectively. The hemin-ZnO-PPy-Pt electrode exhibited 3-fold enhanced electrocatalytic activity towards NO(x) compared to the hemin-PPy-Pt electrode. The electrocatalytic response of the sensor was proportional to the NO(x) concentration in the range of 0.8 to 2000 µM (r(2) = 0.9974) with a sensitivity of 0.04 µA µM(-1) cm(-2) and detection limit of 0.8 µM for the hemin-ZnO-PPy-Pt electrode. The low detection limit, wide linear range and enhanced sensitivity of the present sensor make it valuable for potential applications. In addition, this sensor exhibited good reproducibility and stability.

Theoretical investigation of quinone metabolites of dopamine interaction with DNA--insights into toxicological effects.

Dopamine (3,4-dihydroxyphenylethylamine, DA), an important neurotransmitter, exists in the cell bodies of the dopaminergic neurons of the substantia nigra. Oxidation of DA to its quinone and subsequent reaction with Adenine and Guanine in DNA result in the formation of depurinating adducts, thus causing DNA damage. In this article, we investigate the interaction of quinone metabolites of dopamine (DMQ) with models representing the structure of DNA using dispersion corrected density functional theory with an aim to evaluate the associated structural changes in DNA upon their interaction. Various binding sites for the DA metabolite on these DNA models have been considered and our computations on the activation barriers allowed us to identify preferential bonding sites for these metabolites analogous to experiments. Analysis of the geometry of these adducts in comparison to free base pairs reveals that the attack of DMQ causes remarkable changes in the structural properties. With our calculations, we propose that these structural alterations induce mutations by favoring the formation of depurinating adducts leading to mutagenic effects such as base mispairing, explaining the toxicological (carcinogenic and neurotoxic) behavior of DMQ.

Copper nanoparticles entrapped in SWCNT-PPy nanocomposite on Pt electrode as NOx electrochemical sensor.

A highly sensitive NO(x) sensor was designed and developed by electrochemical incorporation of copper nanoparticles (CuNP) on single-walled carbon nanotubes (SWCNT)-polypyrrole (PPy) nanocomposite modified Pt electrode. The modified electrodes were characterized by scanning electron microscopy and energy dispersive X-ray analysis. Further, the electrochemical behavior of the CuNP-SWCNT-PPy-Pt electrode was investigated by cyclic voltammetry. It exhibited the characteristic CuNP reversible redox peaks at -0.15 V and -0.3 V vs. Ag/AgCl respectively. The electrocatalytic activity of the CuNP-SWCNT-PPy-Pt electrode towards NO(x) is four-fold than the CuNP-PPy-Pt electrode. These results clearly revealed that the SWCNT-PPy nanocomposite facilitated the electron transfer from CuNP to Pt electrode and provided an electrochemical approach for the determination of NO(x). A linear dependence (r(2)=0.9946) on the NO(x) concentrations ranging from 0.7 to 2000 µM, with a sensitivity of 0.22 ± 0.002 µA µM(-1)cm(-2) and detection limit of 0.7 µM was observed for the CuNP-SWCNT-PPy-Pt electrode. In addition, the sensor exhibited good reproducibility and retained stability over a period of one month.

Simultaneous electrochemical determination of superoxide anion radical and nitrite using Cu,ZnSOD immobilized on carbon nanotube in polypyrrole matrix.

A novel highly sensitive biosensor for the direct and simultaneous determination of superoxide anion radical (O2-) and nitrite (NO2-) was developed by incorporation of carbon nanotube (CNT) solubilized in nafion in polypyrrole (PPy) matrix on Pt electrode followed by immobilization of Cu,ZnSOD (SOD1) on it. The CNT/PPy nanocomposite electrode enhanced the immobilization of SOD1 and promoted the electron transfer of SOD1 minimizing its fouling effect. The surface morphological images of PPy and CNT-PPy nanocomposite on Pt electrode were obtained by scanning electron microscopy exhibiting highly microporous structures. The electrochemical behavior of the biosensor investigated by cyclic voltammetry revealed that the SOD1 immobilized electrode showed characteristic of SOD1 quasi-reversible redox peaks with a formal potential of +0.065 V vs. Ag/AgCl. The biosensor exhibited a linear response over the concentration range from 0.1 to 750 µM, with a detection limit of 0.1±0.03 µM for O2- and a corresponding linear range of 0.5-2000 µM, with a detection limit of 0.5±0.025 µM for NO2-. In addition, the biosensor exhibited high sensitivity, good reproducibility and retained stability over 30 days. This modified electrode was quite effective not only in detecting O2- and NO2- independently but also determining the concentration of O2- and NO2- simultaneously in vitro and from cancer cells.

Time-dependant protective effects of mangenese(III) tetrakis (1-methyl-4-pyridyl) porphyrin on mitochondrial function following renal ischemia-reperfusion injury.

This study examined the time-dependent effects of a cell permeable SOD mimetic, MnTMPyP, on mitochondrial function in renal ischemia-reperfusion injury (IRI). Male SD rats were subject to either sham operation or bilateral renal ischemia for 45 min followed by reperfusion for 1, 4 or 24 h. A sub-set of animals was treated with either saline vehicle or 5 mg/Kg of MnTMPyP (i.p.). EPR measurements showed that at 1-h reperfusion MnTMPyP prevented a decrease in aconitase activity (p < 0.05) and attenuated the increase in the high spin heme at g = 6 and oxidation of 4Fe4S to 3Fe4S signal at g = 2.015 (p < 0.01). MnTMPyP was effective in preventing loss of mitochondrial complexes and prevented the loss of cytochrome c and Smac/Diablo from mitochondria early in reperfusion. Following 24 h of reperfusion MnTMPyP was effective in attenuating caspase-3 and blocking apoptosis (p < 0.05). In conclusion, MnTMPyP has biphasic effects in renal IRI, inhibiting mitochondrial dysfunction at the early phases of reperfusion and prevention of apoptosis following longer durations of reperfusion.