In this paper, a simple method for immobilization of acetylcholinesterase (AChE) on cysteamine self assembled monolayers modified gold electrode coupled with CdTe quantum dots (QDs) was proposed and thus a sensitive, fast and stable amperometric biosensor for quantitative determination of carbaryl was developed, The fabrication procedure was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and fluorescence spectrum. The nanoparticles of CdTe QDs led to an increased effective surface area for immobilization of enzyme and their electrocatalytic activity promoted electron transfer reactions and catalyzed the electro-oxidation of thiocholine, thus amplifying the detection sensitivity. Due to the notable decrease in voltammetric signal of the immobilized AChE, a simple method for determination of carbaryl was established. The inhibition of carbaryl was proportional to its concentration in two ranges, from 1 to 50 ng mL(-1) and from 50 to 500 ng mL(-1), with a detection limit of 0.6 ng mL(-1). The constructed biosensor which processes prominent characteristics and performance. such as good precision and reproducibility, acceptable stability and accuracy, fast response and low detection limit, has potential application in the characterization of enzyme inhibitors and detection of toxic compounds against to enzyme. (C) 2008 Elsevier B.V. All rights reserved.