Cu/Mn Double-Doped CeO₂ Nanocomposites as Signal Tags and Signal Amplifiers for Sensitive Electrochemical Detection of Procalcitonin

Nanomaterials themselves as redox probes and nanocatalysts have many advantages for electrochemical biosensors. However, most nanomaterials with excellent catalytic activity cannot be directly used as redox probe to construct electrochemical biosensor because the redox signal of these nanomaterials can only be obtained in strong acid or alkali solution at high positive or negative potential, which greatly limits their applications in biologic assay. In this study, Cu/Mn double-doped CeO₂ nanocomposite (CuMn-CeO₂) was synthesized to use as signal tags and signal amplifiers for the construction of electrochemical immunosensor for sensitive assay of procalcitonin (PCT). Herein, CuMn-CeO₂ not only possesses excellent catalytic activity toward H₂O₂ for signal amplification, but also can be directly used as redox probe for electrochemical signal readout achieved in neutral mild buffer solution at low positive potential. Importantly, since doping Cu, Mn into CeO₂ lattice structure can generate extra oxygen vacancies, the redox and catalytic performance of obtained CuMn-CeO₂ was much better than that of pure CeO₂, which improves the performance of proposed immunosensor. Furthermore, CuMn-CeO₂ can be implemented as a matrix for immobilizing amounts of secondary antibody anti-PCT by forming ester-like bridging between carboxylic groups of Ab₂ and CeO₂ without extra chemical modifications, which greatly simplifies the preparative steps. The prepared immunosensor exhibited a wide linear range of 0.1 pg mL^–1 to 36.0 ng mL^–1 with a low detection limit of 0.03 pg mL^–1. This study implements nanomaterial themselves as redox probes and signal amplifiers and paves a new way for constructing electrochemical immunosensor