An in-field assembled hierarchical mesoporous electroenzymatic sensor for sensitive and real-time monitoring of nitrite

Electroenzymatic sensors are promising for nitrite detection but their application in real environmental scenarios is restricted due to the challenges in fabrication complexity and storage stability. Herein, we proposed a “drop & go” strategy to allow non-professionals to fabricate the electroenzymatic sensors in-field for monitoring the nitrite in real-time. To achieve this, hierarchical mesoporous ITO ( meso ITO) electrode was prepared via a sol-gel process and a nitrite reductase NrfA originated from Shewanella oneidensis MR-1 was immobilized via a simple dropping process. Cyclic voltammetric (CV) analyses confirmed the direct electron transfer between NrfA and meso ITO electrode. After optimizing the enzyme dosage and electrochemical parameters, both CV and amperometric assays for nitrite detection were developed and a linear detection range of 10–130 μM and 1–140 μM nitrite were determined, respectively. Besides, these electroenzymatic sensors exhibited excellent resistance to the common anions in the water and good performance stability under working conditions. With this basis, the fabricated biosensors were applied for continuously monitoring the nitrite in a denitrifying process and the results were well-matched with the colorimetric method reference. More importantly, the presence of bacterial cells created favorable microenvironment for electroenzymatic nitrite reduction , and promoted the detection of trace nitrite in the bioreactor . This work developed a new methodology for fast electroenzymatic biosensor assembling, facilitate sensitive nitrite quantification in the real environment scenario, and may bring new concept for environment contaminants monitoring in real-time.