A micro IrO_x potentiometric sensor for direct determination of organophosphate pesticides

Organophosphate compounds are widely used as pesticides, insecticides, and chemical warfare agents. Biosensors based on acetylcholinesterase (AChE) inhibition and organophosphorus hydrolase (OPH) hydrolysis have been designed for the detection of organophosphate compounds. Since detection with OPH-based biosensors is more direct than that by biosensors based on AChE inhibition, an IrO_x potentiometric sensor was fabricated for the direct determination of organophosphate pesticides (OPs). Detection was based on sensing the pH change accompanying the enzymatic hydrolysis of OPs. Paraoxonase 1 (PON1) is a family of OPHs that catalyzes the hydrolyses of OPs to release protons, the concentration of which is proportional to the amount of OPs. A potential change in the IrO_x pH-sensing electrode can indicate the presence of OPs. A lower limit of detection for diazinon of 3 μM was obtained. Although this is one to three orders of magnitude higher than that of the measurements based on AChE inhibition for indirect determination, the directness and selectivity of the OP detection are highlights of this potentiometric micro sensor, which make it simpler and quicker.