Single cell level detection of Escherichia coli in microfluidic device

Detection of Escherichia coli K-12 in phosphate buffered saline (PBS) was demonstrated in a Y-channel polydimethylsiloxane (PDMS) microfluidic device through optical fiber monitoring of latex immunoagglutination. The latex immunoagglutination assay was performed for serially diluted E. coli solutions using 0.92-μm highly carboxylated polystyrene particles conjugated with polyclonal anti-E. coli. Pre-treatments such as cell lysis or culturing to enhance the signal were not used. Proximity optical fibers around the view cell of the device were used to quantify the increase in 45° forward light scattering of the immunoagglutinated particles. In order to reduce false positive signals caused by antibodies binding to non-viable E. coli cells or free antigens in solution, target solutions were washed three times, and then the results were compared to non-washing treatments. The detection limit was found to be less than 10 cfu ml^-1 (1 cfu per device) without PBS washing (thus detecting non-viable cells and free antigens), or less than 40 cfu ml^-1 (4 cfu per device) with PBS washing (thus detecting viable E. coli cells only).