ONLINE FLOW SENSOR FOR MEASURING ACETYLCHOLINE COMBINED WITH MICRODIALYSIS SAMPLING PROBE

We have developed an on-line electrochemical sensor for the continuous measurement of acetylcholine (ACh). The sensor comprises a small volu me prereactor containing immobilized choline oxidase (ChOx) and catala se (or horseradish peroxidase, HRP), a small volume enzymatic reactor containing immobilized acetylcholine esterase (AChE) and ChOx and a gl assy carbon electrode modified with Os-polyvinylpyrridine-HRP. The sen sor can measure ACh selectively even when the choline (Ch) concentrati on is more than 1000 times that of ACh, when the ChOx and catalase are immobilized in the prereactor. The sensor shows a wide linear relatio nship from 5 nM to 1 mu M and a detection limit of 5 nM (S/N = 2), whi ch is comparable to the ACh detection limit achieved by liquid chromat ography/electrochemistry. It also shows high selectivity against other neurotransmitters and interferents. The properties of the sensor comb ined with a microdialysis (MD) probe were also studied by measuring a solution containing a much higher concentration of Ch than ACh.