Biointerfacial impedance limited ionic gating in a printed microbial electrochemical transistor for BOM evaluation

Monitoring biodegradable organic matter (BOM) is crucial for environmental evaluation, yet microbial electrochemical sensors frequently encounter signal drift and limited stability. Here, we report a printed coplanar microbial electrochemical transistor (pMECT) that operates in a biointerfacial impedance-limited ionic gating regime. A gate bias was applied as an electrochemical selective pressure to enrich electroactive bacteria and establish a stable microbial consortium on the gate. In the coplanar architecture, this stable consortium exhibits low electron-transfer activity and consistent BOM-dependent changes in biointerfacial impedance. The biointerfacial impedance constrains the net ionic charge delivered to the channel, thereby determining the output current under fixed bias. A conductivity-adjusted sodium-acetate matrix-spike test in surface water produced a saturating response to 1–100 mg L −1 in the reference-free configuration, with an approximately 20 min t99-type stabilization criterion for fixed-concentration measurements and no obvious current variation over 1 week under the same conditions. These results define a proof-of-concept microbial transistor transduction route for BOM evaluation. This device offers robust fabrication, straightforward inoculation, and disposable electrodes below USD 1. By leveraging a stable gate microbial community, it supports biointerfacial impedance-limited ionic gating as a measurable transduction pathway in microbial electrochemical transistors, providing a basis for further development toward BOM sensing.