Impedimetric method for measuring ultra-low E. coli concentrations in human urine

In this study, we developed an interdigitated gold microelectrode-based impedance sensor to detect Escherichia coli (E. coli) in human urine samples for urinary tract infection (UTI) diagnosis. E. coli growth in human urine samples was successfully monitored during a 12-h culture, and the results showed that the maximum relative changes could be measured at 10 Hz. An equivalent electrical circuit model was used for evaluating the variations in impedance characteristics of bacterial growth. The equivalent circuit analysis indicated that the change in impedance values at low frequencies was caused by double layer capacitance due to bacterial attachment and formation of biofilm on electrode surface in urine. A linear relationship between the impedance change and initial E. coli concentration was obtained with the coefficient of determination R2>0.90 at various growth times of 1, 3, 5, 7, 9 and 12 h in urine. Thus our sensor is capable of detecting a wide range of E. coli concentration, 7×100 to 7×108 cells/ml, in urine samples with high sensitivity.