Gold nanoclusters decorated hollow ZIF-8 encapsulating iron-catecholates as oxidase mimetics for ratiometric colorimetric detection of nitrite

Gold nanoclusters decorated hollow ZIF-8 encapsulating iron-catecholates (Fe-HHTP@HZIF-8@ AuNCs) was formed through self-assembly of Fe³⁺ and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP), in situ embedding of ZIF-8, and Au³⁺-Zn²⁺ exchange reaction. Its morphology and structure were fully characterized by high-resolution transmission electron microscopy, X-ray diffraction, transmission electron microscopy element mapping, and X-ray photoelectron spectroscopy. Additionally, its oxidase-like activity was explored with K_m of 0.21 mM and V_max of 1.74 × 10⁻⁶ M·s⁻¹ toward 3,3′,5,5′-tetramethylbenzidine (TMB). Due to its excellent catalytic activity and nitrite mediated diazotization of oxTMB, a ratiometric colorimetric method for nitrite detection was established and validated with wide linear range (2.0–400.0 μM), low LOD (0.12 μM), high accuracy (recovery of 95.11–102.14%), and good selectivity. This method was then utilized to determine the nitrite content in sausages and tap water. This study provided a new idea for developing efficient nanozymes and offered an accurate approach for nitrite determination.