Enzyme Modified Carbon Nanotube Biosensors for Pesticide Detection

A simple approach is described for design and development of highly sensitive and stable electrochemical biosensor for direct detection of organophosphate pesticides. Organophosphorus hydrolase (OPH) functionalized single and multi-walled carbon nanotube (CNT) conjugates provided the platform for direct amperometric detection of Paraoxon, a model organophosphate. The catalytic hydrolysis of paraoxon produces equimoles of p-nitrophenol whose oxidation was monitored amperometrically in real time under flow-injection (FIA) mode. Buffer pH, flow rate and method of OPH immobilization were found to influence the sensitivity of paraoxon detection. The dynamic concentration range was 0.5 to 8.5 mmol L^-1 with a detection limit of 2.3 mmol L^-1 (S/N = 3). Our studies show that immobilized enzyme retains a significant degree of enzymatic activity, provided high sensitivity and showed remarkable stability with only 8% decrease in signal over 10-day period. These results suggest that covalent immobilization of OPH on CNT can be used for specific immobilization of OPH with advantages of low price, simplicity and biocompatibility.