The ermsslon intensity of the fluorophore mtrobenzoxa&azoled~palnutoylphosphaUylethanolanune (NBD-PE) 1s sensitive to the local environmental structure when this species is present as a component of an amplnphllz membrane The physxal and electrostatic structure of a membrane may be modulated by selective reactions whxh Induce electrostatic changes at the surface of the membrane The resultmg change III the fluorescence signal may then be used to momtor the concentration of an analyte which is present in solutmn The membrane-associated enzyme acetylcholmesterase (AChE) hydrolyses acetylchohne (ACh) to produce acetic acid and choline The reaction of ACh v&h AChE was detected using a monolayer conslstmg of fatty acids of C1s cham length whxh were covalently attached to quartz wafers and which contained a small amount of NBD-PE (partItIoned from water mto the membrane) The enzyme-substrate reaction produced decreases m fluorescence mtensity from the monolayer, and the detection system was sensltrve to changes m bulk concentration of ACh as small as 0 1 PM, wth a lnmt of detection of 2 FM ACh The mechamsm of transduction of the enzymatx reactlon was mvestlgated usmg spectrofluornnetric methods and fluorescence microscopy ZGywonis Fluornnetry, Acetylchohnesterase, Amplnplules, Enzyme-substrate reactions, Wrobenzoxachazoled1-palm~toylphosphat~dylethanolamme