Ultrasensitive detection of organophosphate insecticides by carbon nanotube field-effect transistor

Carbon nanotube sensors were capable of detecting organophosphate insecticide binding to recombinant acetylcholinesterase (rAChE) immobilized on the sensor. The carbon nanotube sensors were fabricated by chemical vapor deposition method and it showed field-effect transistor property. rAChE was immobilized by specific binding of NTA-Ni and His tag on the reverse side of the carbon nanotube sensor. The current between the source and drain was measured after incubation of various concentrations of organophosphates with immobilized rAChE. Ids–Vgate curves were obtained by plotting the current as a function of the potential applied to the back gate. The Ids–Vgate curves showed a positive shift in a dose dependent manner, while no shifts were observed when an herbicide was added to the sensor and organophosphates were withdrawn on recombinant calmodulin immobilized surface. In spite of different inhibition effects, two organophosphates showed similar dose response curves in measuring Ids–Vgate correlation with the rAChE-immobilized CNT sensors, suggesting that the binding of organophosphates to rAChE may be sequestered from the inhibition activity of those to the enzyme.