Flower-like CeO2/CoO p–n Heterojuncted Nanocomposites with Enhanced Peroxidase-Mimicking Activity for l-Cysteine Sensing

Designing an efficient peroxidase mimic and understanding its catalytic mechanism are of great importance for colorimetric biosensing. Herein, a series of CeO2/CoO nanocomposites (NCs) were prepared using a simple two-step method and applied as peroxidase mimics. Especially, the flower-like 0.10CeO2/CoO NCs (molar ratio of Ce3+/Co2+ salts of 0.10) exhibited much higher peroxidase-mimicking activity than the individual CoO nanoparticles and CeO2 nanoparticles (NPs) and other NCs. The 0.10CeO2/CoO NCs showed high affinity toward H2O2 (Km = 0.245 mM and Vmax = 14.78 × 10–8 M s–1) and TMB (Km = 0.113 mM and Vmax = 110.1 × 10–8 M s–1), thus exhibiting excellent fast response performance. In addition, the stability, repeatability, and durability performances have also been verified. As a result, a sensitive and selective colorimetric sensor was exploited on the basis of 0.10CeO2/CoO NCs for l-cysteine (Cys) detection, which exhibited a linear response to Cys ranging from 5 to 10 μM with a detection limit (LOD) of 3.71 μM. The superior catalytic performance of 0.10CeO2/CoO NCs can be attributed to the highly dispersed mesoporous structure, well-designed p–n heterojunction, and plentiful surface-active species. The possible catalytic mechanism was proposed according to the band gap structures of CeO2 and CoO as well as the free radical tests.