Detection of bacterial metabolism in lag-phase using impedance spectroscopy of agar-integrated 3D microelectrodes.

Abstract Traditional methods for detection of metabolically-active bacterial cells, while effective, require several days to complete. Development of sensitive electrical biosensors is highly desirable for rapid detection and counting of pathogens in food, water, or clinical samples. Herein, we develop a highly-sensitive non-Faradaic impedance sensor which detects metabolic activity of E. coli cells in a mere 1 μl of sample volume and without any sample filtration/purification. The three dimensional (3D) interdigitated electrodes (IDEs) along with self-assembled gold-nickel (Au-Ni) nanostructures significantly amplify the sensitivity by increasing the sensing area almost three-fold. The developed microsystem is integrated with an agar-based growth medium and monitors the metabolism of bacterial cells, enabling bacterial detection in approximately one hour after inoculation, i.e. in the lag-phase. Incorporation of a secondary agar layer as a biocompatible passivation layer protects the IDEs from potential Faradaic reactions and enhances sensitivity to modulation of the non-Faradaic impedance due to cellular metabolism. The resultant label-free sensor is capable of selective identification of metabolizing cells (vs. dead cells) across a wide linear range (10–1000 cells/μl). These results help pave the way for rapid antibacterial susceptibility testing at the point-of-need, which is currently a major challenge in healthcare. Highlights • Non-Faradaic impedance sensor selectively detects metabolism of 10 cells/μl of E. co li K12 in just 1 h. • Metabolism is detected in lag-phase, as opposed to log-phase which takes significantly longer time. • 3D gold-nickel microelectrodes increase sensing area almost three-fold. • Sensor performance is improved by integration with a gel-based passivation layer. • Integration with gel-based culture medium enables in situ detection, with no sample preparation. [ABSTRACT FROM AUTHOR]