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 flowerlike 0.10CeO(2)/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 0.10CeO(2)/CoO NCs showed high affinity toward H2O2 (K-m = 0.245 mM and V-max = 14.78 x 10(-8) M s(-1)) and TMB (K-m = 0.113 mM and V-max = 110.1 x 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 0.10CeO(2)/CoO NCs for L-cysteine (Cys) detection, which exhibited a linear response to Cys ranging from 5 to 10 mu M with a detection limit (LOD) of 3.71 mu M. The superior catalytic performance of 0.10CeO(2)/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.