Microorganisms are associated with the food we eat and with various kinds of animal and human diseases. Often after the initial infection, the concentration of bacteria in our sample of interest (fruit juice, milk, blood etc) is low (≤100 CFU/ml). Being able to detect them quickly at low concentrations would enable us to take preventive action faster and avert harmful effects. Classical techniques for detecting bacteria (plate culture) are slow, tedious and labor intensive. Automated approaches (biosensors and microfluidic systems) are not able to detect target pathogens quickly at low concentrations - primarily because of low volume fraction of the pathogens and/or the time they take to diffuse to a sensor surface. Our microfluidic detection system provides a means to meet this "real world" need - of being able to rapidly (<4 hours) detect the presence of low concentrations (<100 CFU/ml) of bacteria in samples such as fruit juice, milk and blood.

The technique relies on the fact that bacteria can store large amount of charge and thus increase the bulk capacitance of the liquid in which they are suspended. An increase in the number of bacteria results in an increase in the bulk capacitance of the suspension. Taking measurements at multiple frequencies from 40-100 MHz enables us to accurately measure the bulk capacitance of a suspension - and hence detect bacterial proliferations at low levels of infestations within estimated 3-4 cycles of division (~1.5 to 2 hours for E coli).