A ratiometric electrochemical biosensor via alkaline phosphatase mediated dissolution of nano-MnO2 and Ru(III) redox recycling for the determination of dimethoate

A sensitive and ratiometric electrochemical biosensor was developed for the determination of dimethoate via alkaline phosphatase (ALP) mediated dissolution of nano-MnO 2 and [Ru(NH 3 ) 6 ] 3+ (Ru(III)) redox recycling. The electroactive probe Ru(III) was adsorbed on the nano-MnO 2 with the high specific surface area through electrostatic interaction to form the MnO 2 -Ru(III) nanocomposite, which was then fixed on the surface of the glassy carbon electrode. When the dimethoate inhibited the catalytic activity of ALP in a homogeneous system, the hydrolysate L -ascorbic acid (AA) produced by ALP hydrolysis of L -ascorbic acid-trisodium 2-phosphate (AAP) decreased. The solution was then incubated with a glassy carbon electrode modified by MnO 2 -Ru(III). At this time, only a small amount of MnO 2 -Ru(III) was decomposed and Ru(III) was rapidly electroreduced to Ru(II) on the surface of the electrode. The in-situ produced Ru(II) was chemically oxidized back to Ru(III) by Fe(III). The redox recycling of Ru(III) was completed and the Ru(III) reduction current signal was amplified. The process consumed part of Fe(III) to reduce the reduction current signal of Fe(III), and the ratio of the two reduction currents (I Ru(III) /I Fe(III) ) increased significantly. The I Ru(III) /I Fe(III) value increased with the increase of dimethoate concentration in the linear range of 0.01–300 ng mL −1 , and the detection limit was 6.3 pg mL −1 . It has been successfully applied to the determination of dimethoate in oilseed rape and lettuce with a satisfactory result.