Agar-Integrated Three-Dimensional Microelectrodes for On-Chip Impedimetric Monitoring of Bacterial Viability

Monitoring bacterial viability is critical in food safety, clinical microbiology, therapeutics, and microbial fuel cell applications. Traditional techniques for detecting and counting viable cells are slow, require expensive and bulky analytical tools and labeling agents, or are destructive to cells. Development of low-cost, portable diagnostics to enable label-free detection and in situ probing of bacterial viability can significantly advance the biomedical field (both applied and basic research). We developed a highly sensitive method for the detection of bacterial viability based on their metabolic activity using non-Faradaic impedimetric sensors comprised of three-dimensional (3D) interdigitated microelectrodes (3D-IDME). Specifically, the 3D-IDME is modified with electrolessly deposited gold (Au) nanoparticles which amplify the sensitivity by increasing the sensing area. A nutrient-rich agarose gel as the seeding layer is integrated with the sensor to enable direct culturing of bacteria and probing of their metabolic activity in situ. The proposed platform enables monitoring of bacterial viability, even in lag-phase, as they metabolize and release ionic species into the surrounding environment (nutrient agar layer). The sensor can detect down to 10⁴ CFU/mL (~2.5 CFU/mm²) of Escherichia coli K12 (a model strain) in under 1 h without the need for any labeling. By integrating these sensors with agar layers containing different types/concentrations of antibacterial agents, this work can be expanded to enable rapid, high-throughput antibacterial susceptibility testing which can in turn assist caregivers in early prescription of the right treatment to patients with clinical conditions.