Proton-capture strategy for stable redox potential in luteolin detection using SnO₂-ZIF-67 electrodes

Variations in H⁺ concentration significantly impact the redox potential of luteolin during electrochemical sensor detection, leading to indeterminate electrochemical signals and hindering accurate identification of luteolin. In this study, we developed a proton-capture strategy for electrochemical sensing by synthesizing a ZIF-67-modified SnO₂ (SnO₂-ZIF-67) composite, enabling constant peak potential detection across a range of pH environments. We demonstrated through both experimental methods and density functional theory (DFT) that ZIF-67 induces a high density of oxygen vacancies within the SnO₂ crystal, which capture protons dissociated from luteolin, thereby preventing potential shifts during electrochemical detection. We proved that the reaction of luteolin on the SnO₂-ZIF-67 modified electrode involves the transfer of two electrons and two protons, with a charge transfer coefficient of 0.58. The SnO₂-ZIF-67 modified sensing electrode exhibits a record-high sensitivity of 218.7 μA μM⁻¹ for luteolin detection, with an ultra-low detection limit of 0.12 nM. Furthermore, the sensor shows excellent selectivity for luteolin, with common coexisting ions and compounds causing no significant interference. The sensing electrode also demonstrates exceptional stability, retaining 94.5 % of its initial signal after four weeks of exposure to air, and it accurately detects luteolin in real samples, highlighting its great potential for practical applications.