Surface functionalization of Fe/Cu–Co3O4 catalyst with enhanced interfacial activity for nitrite sensing with potential in portable applications

Nitrite is a common harmful ion found in water and food, and its excessive intake poses significant risks to human health. Accordingly, devising a detection strategy for nitrite that is fast, highly responsive, durable, and ecologically sustainable holds significant importance. In this study, a surface-modified Fe/Cu bimetal-doped Co 3 O 4 catalyst was successfully synthesized, and its 1 wt% aqueous dispersion was drop-cast onto carbon cloth (CC) to fabricate a binder-free flexible electrode (KH792@(C)Fe/Cu–Co 3 O 4 CC) for electrochemical sensing of nitrite. This electrode demonstrated remarkable electrocatalytic activity toward NO 2 − in phosphate buffer solution (0.1 M PBS, pH 7.4), offering a broad linear detection range (6.65 μM–5.0 mM), an exceptionally rapid response time (0.1 s), as well as a low detection limit of 6.65 μM, demonstrating both its high sensitivity and practical applicability. This enhanced performance is largely credited to the cooperative effect between KH792 functional organic units and the Fe/Cu–Co 3 O 4 composite oxide framework. On one hand, the introduction of organic molecules enhances the electrode's electron transfer capability and surface hydrophilicity. On the other hand, the dual-metal doping induces a high density of surface defects and oxygen vacancies, enhancing the density of active sites and facilitating both the adsorption and electron transport processes of nitrite. Moreover, the catalyst was successfully applied to commercial disposable screen-printed electrodes, which were compatible with portable electrochemical workstations, underscoring its potential for low-cost and on-site nitrite detection.