Whole cell biosensors, which have been genetically engineered to respond to environmental stress, trigger a sequence of processes, which leads to generation of electrical current. This work presents a mathematical model describing the kinetic properties of the bacterial enzymatic reactions in response to toxic chemicals, and the resulting electro-active molecule diffusion to the electrode in a miniaturized electrochemical cell. The model characterizes the generated electrical current as a function of bacteria and toxicant concentrations, electrochemical cell dimensions and electrode dimensions. A model was framed for a 100 nL spherical electrochemical cell. Its performance was simulated and compared to experimental data. This simulation results agreed well with the measured data and therefore it should be useful in predicting current variations in similar systems with different geometries, materials and biological components. (c) 2006 Elsevier B.V. All rights reserved.