RESEARCH ARTICLE Copyright © 2011 American Scientific Publishers All rights reserved Printed in the United States of America SENSOR LETTERS Vol. 9, 1–7, 2011 Electrochemical Sensor for Simultaneous Measurement of Nitrite and Superoxide Anion Radical Using Superoxide Dismutase-Mimetic Manganese(III) Tetrakis(1-methyl-4-pyridyl)Porphyrin on Polypyrrole Matrix Seenivasan Rajesh 1† , Niroj Kumar Sethy 2 , Kalpana Bhargava 2 , Govindaswamy Ilavazhagan 2 , Sushil Kumar Singh 3 , and Chandran Karunakaran 1 ∗ 1 Biomedical Research Laboratory, Department of Chemistry, VHNSN College, Virudhunagar–626 001, Tamil Nadu, India 2 Peptide and Proteomics Division, Defence Institute of Physiology and Allied Sciences (DIPAS), New Delhi–110 054, India 3 Si-MEMS Division, Solid State Physics Laboratory (SSPL), New Delhi–110 054, India (Received: 16 March 2011. Accepted: 28 June 2011) An electrochemical highly sensitive nitrite (NO - 2  and superoxide anion radical (O •- 2  sensor was fabricated and developed based on an electrochemical deposition of manganese(III) tetrakis(1- methyl-4-pyridyl)porphyrin (MnTMPyP) in polypyrrole (PPy) matrix on Pt electrode. The surface morphological image of MnTMPyP-PPy and PPy matrix on Pt electrode was obtained by scan- ning electron microscopy exhibiting microporous structure. The electrochemical behavior of the MnTMPyP-PPy-Pt electrode as sensor investigated by cyclic voltammetry revealed that the char- acteristic of MnTMPyP reversible redox peaks obtained at -0.12 V and -0.38 V versus Ag/AgCl respectively. The sensor electrode showed an excellent electrocatalytic nitrite oxidase and super- oxide dismutase (SOD) activities. This electrochemical sensor exhibited a linear current response over the concentration range from 0.8 to 1000 M, with a detection limit of 08 ± 003 M for NO - 2 and a corresponding linear range from 0.6 to 1000 M, with a detection limit of 06 ± 002 M for O •- 2 . In addition, the sensor displayed high sensitivity, good reproducibility and retained stability over a period of ∼4 weeks. This SOD-mimetic electrode was proved to be effective not only in detecting NO - 2 and O •- 2 independently but also in determining the concentrations of NO - 2 and O •- 2 simultaneously in in vitro systems. Keywords: SOD-Mimetic, MnTMPyP, NO - 2 and O •- 2 Sensor, Polypyrrole Matrix. 1. INTRODUCTION Nitric oxide (NO) and superoxide anion radical (O •- 2  is the primary species of reactive nitrogen species (RNS) and reactive oxygen species (ROS) respectively, pro- duced ubiquitously in biological systems. 1 Both nitrite (NO - 2 /nitrate (NO - 3  are the end products of NO biosyn- thesis pathway and can be converted to NO during oxy- gen limiting conditions. 23 NO metabolites viz., nitrite ∗ Corresponding author; E-mail: ckaru2000@gmail.com † Present Address: Department of Bio-technology, MEPCO Schlenk Engineering College, Sivakasi–626 005, India. (NO - 2 /nitrate (NO - 3  are also involved in the biosyn- thesis of NO. 4 Estimation of NO - 2 is being used to measure the endogenous nitric oxide synthase (NOS) activity in basic and translational research. 5 Recently, it has been shown that NO - 2 also plays an essential role in cell signaling and pathology whereby distur- bances in steady-state NO - 2 concentrations may have pro- found consequences. 6 Inappropriate production of NO and their metabolites of NO - 2 /NO - 3 led to the develop- ment of several pathologies such as cardiovascular dys- functions, arteriosclerosis, ischemia and neurodegenerative diseases. 7–11 There are several enzymatic and nonenzy- matic pathways for the one-electron reduction of NO - 2 Sensor Lett. 2011, Vol. 9, No. 5 1546-198X/2011/9/001/007 doi:10.1166/sl.2011.1733 1