Si
doped CoO nanorods (denoted as Si-CoO) were prepared by the
hydrothermal method. The Si-CoO composites were characterized by X-ray
diffraction (XRD), transmission electron microscopy (TEM), scanning
electron microscopy (SEM), and X-ray photoelectron spectra (XPS),
etc. The results suggest that Si element uniformly distributed onto
CoO nanorods with a diameter of 50–100 nm. The as-prepared
Si-CoO nanocomposite possessed an excellent peroxidase-like activity
as well as quickly catalyzed the colorless substrate 3,3,5,5-tetramethylbenzidine
(TMB) to be oxidized into blue oxTMB by H2O2 only in 20 s, which was easily visually observed. The electron spin
resonance (ESR) data confirms that superoxide radicals (•O2
–) play a key function in catalytic reaction.
On the basis of the peroxidase biomimetic activity of Si-CoO, we constructed
a new biosensor for detection of H2O2 and reduced
glutathione (GSH) in the range of 1–100 uM with a limit of
0.22 and 0.45 uM, respectively.
Designing an efficient peroxidase mimic and understanding its catalytic mechanism are of great importance for colorimetric biosensing. Herein, a series of CeO 2 /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 Ce 3+ /Co 2+ salts of 0.10) exhibited much higher peroxidase-mimicking activity than the individual CoO nanoparticles and CeO 2 nanoparticles (NPs) and other NCs. The 0.10CeO 2 /CoO NCs showed high affinity toward H 2 O 2 (K m = 0.245 mM and V max = 14.78 × 10 −8 M s −1 ) and TMB (K m = 0.113 mM and V max = 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 0.10CeO 2 /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 0.10CeO 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 CeO 2 and CoO as well as the free radical tests.
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