A cell-based protein-detecting array was developed on which genetically engineered microbes were spatially organized as sensor elements in a microfluidic device. Whole E. coli cells displaying protein-binding peptide ligands at high density on their outer membrane served as effective capture reagents. Cells were immobilized on gold electrodes using dielectrophoresis, thus allowing each sensor element to be electrically addressable. On-chip fluorescence analysis and flow cytometry were used to confirm highly specific capture of target molecules. The use of dielectrophoresis in microfluidic devices enabled efficient utilization of whole-cell capture reagents for a variety of protein detection and diagnostic applications.