Multifunction nanoenzyme-assisted ion-selective and oxidation catalysis SERS biosensors for point-of-care nitrite testing

Point-of-care testing (POCT) for nitrite has significant implications for the diagnosis, treatment, and prognosis of various diseases. However, the low polarization and Raman cross section of nitrite present obstacles to monitoring nitrite molecules using the surface-enhanced Raman scattering (SERS) method. In this study, a bionic enzyme (cyanocobalamin (VB12))-modified matrix of metal-organic frameworks (ZIF-67) is chosen as a carrier for loading Au colloid complexes and subsequently utilized as ion-selective SERS biosensors (ADA@ZIF-67 bionic enzyme biosensors). By leveraging the mixed-state of the cobalt (Co) element, the as-prepared biosensors have demonstrated dual-mode nanoenzyme properties, providing increased peroxide activity for nitrite oxidation. Simultaneously, the presence of the distinct bionic state Co in the biosensors enables the ion-selective capture of nitrite. When utilized as a POCT reagent, the biosensors demonstrate high sensitivity, with a detection limit of 1.67 nM for nitrite and a wide linear response range of nitrite spanning from 1 M to 100 nM. Real salivary samples, encompassing varied activities such as working, eating, exercising, and sleeping, are evaluated using the proposed method and commercially available nitrite kits. The SERS biosensors demonstrate superior performance and hold promise as a potential tool for POCT, detection, and healthcare applications.