Electrochemical Nanoneedle Biosensor Based on Multiwall Carbon Nanotube

Comparison of pesticide sensitivity by electrochemical test based on acetylcholinesterase biosensor

Based on the change in electrochemical behavior of enzymatic activity induced by pesticide, a novel electrochemical method has been devised for investigation of pesticide sensitivity using acetylcholinesterase (AChE) biosensor. Because of the excellent biocompatibility and good stability of chitosan matrix, it prevented leakage of the AChE from electrode. Multiwall carbon nanotube (MWNT) promoted electron transfer reaction at a lower potential and catalyzed the electro-oxidation of thiocholine, thus amplifying the sensitivity and amperometric response of the biosensor. Four pesticides of carbaryl, malathion, dimethoate and monocrotophos were selected to discuss their inhibition efficiencies to AChE. The inhibition curves were similar to Michealis-Menten and the Michealis-Menten constants (Km) were calculated to be 0.96 microM, 1.78 microM, 1.97 microM and 4.28 microM, respectively. Ninety-five percent reactivation of the inhibited AChE could be regenerated using pralidoxime iodide within 8 min. The proposed electrochemical pesticide sensitivity test exhibited high sensitivity, low cost and simplified procedures, which is a promising new tool for comparison of pesticide sensitivity and for selection of the most efficient enzyme inhibitors.

The advantage of using carbon nanotubes compared with edge plane pyrolytic graphite as an electrode material for oxidase-based biosensors

Carbon nanotubes (CNTs) are promising materials for use in amperometric biosensors. The defect sites at their ends, and on their sidewalls, are considered to be edge plane-like defects and show high electrocatalytic activity toward several biological molecules. However, electrocatalytic activity toward H(2)O(2) has not been compared among bamboo-structured CNTs (BCNTs), which have many defect sites; hollow-structured CNTs (HCNTs), which have few defect sites; edge plane pyrolytic graphite (EPG); and traditional glassy carbon (GC). The advantages of using CNTs in electrodes for biosensors are still equivocal. To confirm the utility of CNTs, we analyzed the electrochemical performance of these four carbon electrodes. The slope of the calibration curve for H(2)O(2) at potentials of both +0.6 V and -0.1 V obtained with a BCNT paste electrode (BCNTPE) was more than 10 times greater than the slopes obtained with an HCNT paste electrode and a GC electrode, reflecting the BCNT's larger number of defect sites. Although the slope with the EPG electrode (EPGE) was about 40 times greater than that with BCNTPE at +0.6 V, the slopes with these two carbon electrodes were nearly equivalent at -0.1 V. EPGE demonstrated excessive electrochemical activity, detecting currents on the basis of consumption of oxygen and oxidation of ascorbic acid, even at -0.1 V. In contrast, BCNTPE could dominantly detect a cathodic current for H(2)O(2) at -0.1 V, even when interfering molecules were added. BCNTPE possesses appropriate electrochemical activity and is an effective electrode materials for developing interference-free oxidase-based biosensors operated by the application of an appropriate potential.