MWCNT-MOF-199-Nafion hybrid platform for low-potential amperometric nitrite sensing

A simple electrochemical sensing platform based on a hybrid composed of multi-walled carbon nanotubes (MWCNTs), MOF-199, and Nafion is reported for the amperometric determination of nitrite at a low potential (- 0.200 V). Most electrochemical nitrite sensors rely on its oxidation at relatively high positive potentials, where the oxidation of coexisting electroactive species may compromise selectivity. The sensing strategy exploits the Cu(II)/Cu(I) redox couple of MOF-199 to mediate the catalytic reduction of nitrite, while MWCNTs provide an efficient conductive network that facilitates electron transfer. Nafion promotes homogeneous dispersion of the hybrid components, improves interfacial contact, and enhances the structural stability of the sensing layer, resulting in a robust architecture. Under the optimized experimental conditions, the proposed sensor exhibited a sensitivity of (2.60 ± 0.03) µA ppm⁻¹, a detection limit of 21 ppb (0.45 µM), a wide linear range, good reproducibility intra-hybrid (RSD = 7.7%) and inter-hybrid (RSD = 2.6%), excellent long-term stability, and negligible interference from common inorganic ions and electroactive compounds. The practical applicability of the sensing platform was successfully demonstrated through nitrite determination in different water samples. The proposed sensing platform combines straightforward fabrication, good analytical performance, and practical applicability. More importantly, it demonstrates that the rational integration of conductive carbon nanostructures with redox-active MOFs provides an effective strategy for developing simple and robust electrochemical sensors operating through catalytic nitrite.