Reusable and storable whole-cell microbial biosensors with a microchemostat platform for in situ on-demand heavy metal detection

Target analyte detection using whole-cell microbial biosensors can benefit from a microchemostat platform owing to the reduced reagent consumption, a finely controllable environment, and multi-parallel processing. However, the use of the previous microchemostat still has limitations for practical applications, e.g., its single-use design, long time requirements for cell and device preparation, low portability, slow and weak response signals, and the lack of ready-to-use in situ devices. In the present study, we developed a novel microchemostat platform that resolves these issues and enhances the performance of microbial biosensors via its abilities to actively control the cell population and to form a uniform culture environment using a nanoscale hydrodynamic film (NHF). The combination of the microchemostat platform and the microbial biosensors yielded fast and strong signals on demand in response to heavy metal ions (e.g., Pb2+). In addition, the platform enables the long-term on-chip storage of microbial biosensors for over 1 month, without deterioration of growth and detection ability. Lastly, we demonstrated that microbial biosensors can consecutively measure multiple samples by a regeneration process in which the microchemostat platform continuously subcultures the microbial biosensors until the complete recovery of their sensing capabilities. Thus, the microchemostat offers whole-cell microbial biosensors that are fast, ready-to-use, reusable, and storable. It also shows good potential for user-friendly, portable on-site environmental monitoring, particularly where expensive analytical tools and/or instruments for heavy metal ion detection are unavailable.