Extended lifetime of reagentless detector for multiple inhibitors of acetylcholinesterase.

Competitive inhibitors of acetylcholinesterase (AChE) are detected using an evanescent wave technique to monitor changes in the absorbance spectrum of an AChE-monosulfonate tetraphenyl porphyrin (TPPS(1)) complex immobilized on the surface of a glass slide. In this technique, porphyrin is displaced from the AChE active site by the inhibitor. The loss in absorbance intensity of the characteristic absorbance peak for the AChE-TPPS(1) complex at 446 nm is linearly dependent on the log of the inhibitor concentration. This technique yields detection limits at 3:1 S/N of 37 ppt for eserine, 50 ppt for galanthamine, 100 ppt for scopolamine, 250 ppt for tetracaine, 45 ppt for diazinon, and 83 ppb for Triton X-100. When stored under vacuum, the enzymatic lifetime of the immobilized AChE surface is greater than 73 days while the responsive lifetime of the immobilized AChE-TPPS(1) surface is currently 49 days.