Two-dimensional MnO₂ And CoOOH As Enzyme Mimetics And Their Application In Antioxidants Detection

With the development of nanotechnology,many nanomaterials were found with enzyme mimicking activity in recent years.These nanomaterials are called nanoenzymes which overcome the disadvantages of low stability and high cost of natural enzymes.Nanozymes show a variety of enzyme-like activity such as peroxidase,catalase,oxidase and superoxide dismutase,which have been widely used in biomedical,analytical,food and environmental fields.Until now,most nanomaterials are reported to possess peroxidase-like activity.However,other species enzyme mimics are less reported and their reaction mechanism is still unclear.In this paper,we mainly researched the enzyme mimicking activity of Mn O₂nanosheet and Co OOH nanoring and their application in antioxidant detection.Firstly,we report a fast and colorimetric method for the detection of antioxidants based on the oxidase-like activity of two-dimensional Mn O₂nanosheets.Specifically,Mn O₂nanosheets can transform the colourless substrate,3,3?,5,5?-tetramethylbenzidine(TMB),to a deep blue product(ox TMB)via catalytic oxidation,with arising a specific absorption peak at 652 nm.In the presence of antioxidants,both the dramatic colour fading and decrease of absorbance at 652 nm are observed owing to the inhibition of catalytic oxidation of TMB,where Mn O₂nanosheets can be transformed to Mn²⁺,meanwhile coupling with the decrease of surface negative charge with the aid of antioxidants.Based on the linear relationship between the absorbance at 652 nm and concentration of the antioxidants,quantitative determination of antioxidants has been achieved.Moreover,combined with a smartphone-based technology,a portable colorimetric analytical platform for antioxidants assay is further developed.Secondly,we developed a new facile method to synthesize Co OOH nanorings and found the prepared Co OOH nanorings possess oxidase-like activity which directly oxidate TMB.Steady-state kinetics research showed that this nanozyme has stronger affinity with TMB than HRP and Co OOH nanosheets.In the present of antioxidants,Co OOH nanorings were reduced to Co²⁺,causing the deprivation of the enzyme-like activity.Subsequently,both color fading and decrease of absorption peak at 652 nm were observed.On the basis of this principle,colorimetric detection of antioxidants,based on Co OOH nanorings,in green tea was successfully constructed.Furthermore,smartphone was used as an analyzer to visual detection of antioxidants by reading out the RGB values of the solution.Finally,based on the oxidase-like activity of Co OOH nanorings,a reliable and colorimetric platform was established for the determination of?-glucosidase activity.In this detection system,the oxidase-like activity of Co OOH nanorings was inhibited by ascorbic acid because Co OOH was reduced to inactive Co²⁺.On the other hand,L-ascorbic acid 2-glucoside can be selectively hydrolyzed by?-glucosidase to release ascorbic acid.Further,we successfully determine the activity of?-glucosidase in human serum.This method broaden the application of Co OOH nanorings and provide a new strategy in?-glucosidase activity determine with the advantage of easy operation,low cost and high sensitivity which is promising to apply in the next generation point-of-care testing.