Simultaneous Bioelectrochemical Detection of Nitrate and Nitrite with a Whole-Cell Hydrogel Electrode

Bioelectrochemical sensors (BES) are promising to specifically detect nitrate or nitrite but never realize simultaneous detection in a single system. In this study, a novel biosensor using self-assembled hydrogel bioelectrodes with reduced graphene oxide (rGO) and genetically engineered electroactive Shewanella species was designed for the simultaneous detection of nitrate and nitrite. The highly conductive rGO rendered a drastically improved reverse electron transfer from the electrode to Shewanella, which achieved a sensitive and quantitative response to nitrite/nitrate. Meanwhile, the genetically engineered Shewanella enabled efficient differentiation of nitrate and nitrite detection in a single system (a sensitivity of 883.48 μA mM^-1 cm^-2 to nitrate with a limit of detection of 0.92 μM and a sensitivity of 888.48 μA mM^-1 cm^-2 to nitrite with a limit of detection of 0.72 μM). The whole-cell biohydrogel based BES also showed excellent anti-interference and long-term storability for plug-and-play application. Based on these properties, this work demonstrated the power of genetically engineered electroactive bacteria in rGO biohydrogel for dual-analyte detection and also provided a new strategy for developing high-performance whole-cell BES for practical environmental monitoring.