A microfluidic biochip has been fabricated to retain a single cell (e.g. a cancerous cell) within a U-shaped cell retention structure for real-time monitoring of cellular changes over long periods of time (hours). Experiments illustrate the cell heterogeneity in drug responses, and demonstrate the significance of the microchip platform for cancer diagnosis. This microdevice provides a clinical diagnostic platform to evaluate multi-drug-resistance in cancer patients. This device may increase the effectiveness of current chemotherapeutic strategies by evaluating an individual’s cellular response to these agents.