Arsenic and other pollutants are often present in trace amounts in drinking water in a number of countries. In aqueous solutions the sensitivity of arsenic-responsive bacterial bioreporters is far better than the performance of chemical field test kits. However, biological detection currently requires extensive handling and expensive fluorescence microscopy. We fabricated and tested microfluidic chips with fluorescent (GFP) E. coil bacteria that respond to arsenic. Measurement results of fluorescence intensity as function of arsenic concentration and exposure time are promising, showing a clear response to concentrations of 50 mu g/l of arsenite.