An amperometric biosensor for chlorphenvinphos (organophosphorus pesticide) based on carbon nanotube paste and acetylcholinesterase enzyme (CNTs-AChE biosensor) is described herein. This CNTs-AChE biosensor was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The SEM result shows the presence of CNTs and small lumps, due to the enzyme AChE, which has a type of cauliflower formation. From EIS analysis is possible to observe increased for CNTs-AChE biosensor when compared to the carbon nanotube paste electrode for the reaction [Fe(CN)6]4？/3？. Using a chronoamperometric procedure, a linear analytical curve was observed in the ？M range with limit of detection of ？M. The determination of chlorphenvinphos in the insecticide sample proved to be in agreement with the standard spectrophotometric method, with a 95% confidence level and with a relative error lower than 3%. In this way, the CNTs-AChE biosensor presented easy preparation, fast response, sensitivity, durability, good repeatability, and reproducibility. 1. Introduction Carbon nanotubes (CNTs) consist of cylindrical graphene sheets with nanometer diameters and present many unique characteristics, such as large ratio of surface area to mass, high electrical conductivity, and remarkable mechanical strength. CNTs include both single-walled and multiwalled structures. Single-wall CNTs (SWCNTs) are comprised of cylindrical graphite sheets of nanoscale diameter capped by hemispherical ends. Multi-wall CNTs (MWCNTs) are comprised of several to tens of incommensurate concentric cylinders of these graphitic shells with a layer spacing of 0.3–0.4？nm. MWCNTs tend to have diameters in the 2–100？nm range and can be considered as a mesoscale graphite system [1]. Since their discovery in 1991 [2], extensive applications have been found in the physical, chemical, and material science fields. The advantages of CNTs, such as their high surface area, favorable electronic properties, and electrocatalytic effect, have recently attracted considerable attention for the construction of electrochemical biosensors. Electrochemical biosensors, particularly enzyme electrodes, have benefited greatly from the ability of CNT-based transducers to promote the electron-transfer reactions of enzymatically generated species, such as hydrogen peroxide [3, 4] or NADH [5], and from the resistance to surface fouling of transducers. Electrochemistry is a powerful tool for real-time detection compared to fluorescence and spectrophotometry, which involves expensive detection systems. A
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