Electric Cell-Impedance Sensing (ECIS) is a real-time transduction system that can be used to detect the presence of foreign particles or pathogens by measuring the changes in impedance or resistance of a cell monolayer grown on an electrode. Herein, we present the use of ECIS for the detection of the toxicity of silver nanoparticles on Madine Derby Canine Kidney (MDCK) epithelial cells as a function of changes in the cell confluence and barrier function of the cell monolayer. The barrier function is a measure of the number of tight junctions formed between confluent cells in a monolayer; tighter confluence leads to an increase in a barrier function and thus in the measured resistance. We were able to detect exposures as low as 1 μg of 20 nm silver nanoparticles per 105 cells within 2 hours; those exposures were quantified as a significant drop in impedance and a gradual decrease in the barrier function as compared to the controls. Future work would include the detection of protein toxins using impedance sensing as well as further analysis of the barrier function using fluorescent staining.