Copper Nanocluster (Cu23 NC)-Based Biomimetic System with Peroxidase Activity

The design of horseradish peroxidase mimicking catalysts is an emerging area of research for clinical diagnosis and biomedical application. Here, blue luminescent, pepsin-templated copper nanoclusters (Cu NCs) are synthesized, which act as an effective peroxidase mimic. The Cu NCs are composed of 23 Cu atoms within one pepsin molecule (Cu23@pepsin) and exhibit intense blue photoluminescence (PL) at 455 nm. The Cu23@pepsin catalyzes H2O2 reduction along with the oxidation of o-phenylenediamine (OPD) following Michaelis–Menten enzyme kinetics. The optimum enzymatic activity of recyclable Cu23@pepsin is obtained at neutral pH at 35 °C. When OPD is oxidized to yield yellow-colored diaminophenazine (DAP) with a PL maximum at 565 nm, a concurrent quenching of Cu23@pepsin emission at 455 nm takes place due to the energy transfer process. The dual PL response of the Cu23@pepsin-based probe is exploited in designing a ratiometric H2O2 sensor. The reactivity toward peroxide is utilized in specific and sensitive sensing of glucose with a limit of detection (LOD) of 7.56 μM. The development of Cu NC-based artificial enzymes will pave the way for versatile biomedical, environmental, and clinical applications.