Rational Design of Cu-Doped Tetrahedron of Spinel Oxide for High-Performance Nitric Oxide Electrochemical Sensor.

The real-time detection of nitric oxide (NO) in living cells is essential to reveal its physiological processes. However, the popular electrochemical detection strategy is limited to the utilization of noble metals. The development of new detection candidates without noble metal species still maintaining excellent catalytic performance has become a big challenge. Herein, we propose a spinel oxide doped with heteroatom-Cu-doped CoO (Cu-CoO) for the sensitive and selective detection of NO release from the living cells. The material is strategically designed with Cu occupying the tetrahedral () center of CoO through the formation of a Cu-O bond. The introduced Cu regulates the local coordination environment and optimizes the electronic structure of CoO, hybridizing with the N 2p orbital to enhance charge transfer. The Cu site can well inhibit the current response to nitrite (NO), resulting in a high improvement in the electrochemical oxidation of NO. The selectivity of Cu-CoO can be markedly improved by the pore size of the molecular sieve and the negative charge on the surface. The rapid transmission of electrons is due to the fact that Cu-CoO can be uniformly and densely in situ grown on Ti foil. The rationally designed Cu-CoO sensor displays excellent catalytic activity toward NO oxidation with a low limit of detection of 2.0 nM (S/N = 3) and high sensitivity of 1.9 μA nM cm in cell culture medium. The Cu-CoO sensor also shows good biocompatibility to monitor the real-time NO release from living cells (human umbilical vein endothelial cells: HUVECs; macrophage: RAW 264.7 cells). It was found that a remarkable response to NO was obtained in different living cells when stimulated by l-arginine (l-Arg). Moreover, the developed biosensor could be used for real-time monitoring of NO released from macrophages polarized to a M1/M2 phenotype. This cheap and convenient doping strategy shows universality and can be used for sensor design of other Cu-doped transition metal materials. The Cu-CoO sensor presents an excellent example through the design of proper materials to implement unique sensing requirements and sheds light on the promising strategy for electrochemical sensor fabrication.