261-265<span style="font-size:11.0pt;line-height:
115%;font-family:Calibri;mso-fareast-font-family:" times="" new="" roman";mso-bidi-font-family:="" "times="" roman";mso-ansi-language:en-us;mso-fareast-language:en-us;="" mso-bidi-language:ar-sa"="" lang="EN-US">A flow injection analysis (FIA) system coupled with an
evanescent wave (EW) sensor employing total internal reflection of fluorescence
radiation (TIRF) for the detection of the organophosphorus compounds is
reported. The detection is based on the measurement of acetylcholinesterase
(AChE) inhibition in the presence of organophosphorus compounds. AChE was
immobilized on controlled pore glass (CPG) particles and packed into a teflon
column which was then coupled to the evanescent wave sensor. A constant
concentration of acetylthiocholine in Tris-HCI buffer (10 mM, pH 7.5)
was pumped through the enzyme column. The thiocholine formed as a result of the
AChE catalyzed reaction in the column was monitored by the injection of
7-diethylamino-3-( 4' -maleimidylphenyl)-4-methylcoumarin (CPM) which forms a
highly fluorescent compound with thiocholine. The CPM-thiocholine complex was
excited with the evanescent wave and the resulting fluorescence was detected by
a Himamastsu S-2387/66R detector. Varying concentrations of paraoxon were
injected through the enzyme column and the extent of enzyme inhibition was
recorded by the injection of the optimum concentration of the CPM. The
difference of the two responses in the presence and absence of the paraoxon
determines the extent of inhibition. The acetycholinesterase activity was then
reactivated by the injection of pyridine 2-aldoxime methiodide (2-PAM) which
results in the recovery of the initial response.</span