In this study, a new amperometric biosensor was developed for the detection of the anti-dementia drugs fortified with tap water. For this purpose, electrocopolymerization of 5,6-bis(octyloxy)-4,7-di(thiophen2-yl)benzo[c][1,2,5]oxadiazole(BODT) with (2-(((9H-fluoren-9-yl)methoxy)carbonylamino) acetic acid (FMOC) on graphite electrode was successfully achieved and used as an immobilization matrix. Acetylcholinesterase (AChE) and choline oxidase (ChO) enzyme couple was immobilized on copolymer coated graphite electrode via covalent binding with the help of carbodiimide chemistry. Changes in the responses of the proposed biosensor based on AChE inhibition were recorded using acetylcholine as the substrate. The bi-enzymatic biosensor based on conducting copolymer showed good linear detection range between 0.01 and 12.0 mM and a detection limit (LOD) of 0.014 mM to acetylcholine. Surface and electrochemical characterization were performed via Scanning Electron Microscopy (SEM) and cyclic voltammetry (CV) techniques. Moreover, the design biosensor system was tested for the detection of neostigmine and donepezil as pharmaceuticals in fortified tap water samples. Very low detection limits of 0.027 mu g/L donepezil and 0.559 mu g/L neostigmine were achieved. The analysis of spiked tap water proved the biosensor capability to be used. The results were found to be in good agreement with the ones determined by HPLC/DAD technique. (C) 2014 Elsevier B.V. All rights reserved.