Simple Electrochemical Method for the On-site Detection of Neurotoxins

A novel electrochemical molecular sensor was fabricated based on the electron-transfer promotion effect of cationic thiol/disulfide molecules on an Au electrode. Nereistoxin (4-N,N-dimethylamino-1,2-dithiolane, NRT) is a naturally occurring neurotoxin bearing disulfide and tertiary amine in its substructure. NRT adsorbed on an Au electrode via the Au-S covalent bond, forming a self-assembled monolayer (SAM). The cationic NRT SAM facilitated electron transfer between the Au electrode and an anionic marker, ferricyanide. This electron-transfer promotion effects were more pronounced under a lower supporting electrolyte (KCl) condition. In the presence of 1 mM KCl, almost a 0/1 contrast of the signals between bare and NRT-modified Au electrode was obtained. On the basis of this phenomenon, we designed an NRT sensor, and succeeded in detecting it quantitatively from human serum with satisfactory sensitivity. The same electron-transfer promotion effect was also found in thiocholine, bearing thiol and quaternary amine. Thiocholine is the product of hydrolysis by cholinesterase from the variant substrates, acetylthiocholine and butyrylthiocholine. The detection of neurotoxic organophosphorus and carbamate compounds through their cholinesterase inhibition effect was performed, and the system was successfully applied to the cholinesterase assay of real human blood samples.