Microfluidic Assay for Continuous Bacteria Detection Using Antimicrobial Peptides and Isotachophoresis

We present a novel microfluidic assay for continuous and quantitative detection of bacteria in water. We leverage isotachophoresis (ITP), an electrophoretic focusing technique, to create a stationary high concentration zone of fluorescently labeled antimicrobial peptides (AMPs) in a microfluidic channel. The tested water sample flows continuously through this high concentration AMPs reaction zone; any bacteria present in the sample is simultaneously labeled by, and separated from, the high concentration AMPs. The labeled bacteria continue into the downstream pure-buffer zone where the fluorescence signal is monitored, providing a direct quantitative measurement of the original bacterial concentration in the sample. We present the principles of the technique, demonstrate its applicability for quantitative detection of E. coli as well as its stability over a 1 h monitoring time, and provide a simple model for predicting its performance at different operating conditions. The method could be potentially expanded for use with other types of probes and provide continuous analysis and monitoring of water samples at the point of need.