Ascorbic acid(AA),also known as vitamin C(Vc),is a type of reducing substance with an enediol structure.Ascorbic acid plays an important role in maintaining the normal physiological functions of the human body.Appropriate intake of ascorbic acid is beneficial to enhance the bodys anti-stress ability and immunity,promote the absorption of calcium,iron,folic acid,etc.,and prevent cancer and cardiovascular disease.In addition,ascorbic acid as an antioxidant is also widely used in the fields of medical pharmacy,food processing and cosmetic products.Therefore,it is very necessary to develop an accurate and sensitive method for ascorbic acid detection.Colorimetric analysis methods based on nanozymes have attracted more and more research interest owing to their fascinating advantages of low cost,good stability,high sensitivity and excellent selectivity.In this paper,a simple,sensitive,rapid and selective colorimetric method for ascorbic acid detection was developed.Inspired by the fact that nanozymes with redox-active metal center are prone to possess good catalytic performance,a novel metal-organic framework nanozyme Ce-BDC was first prepared by using terephthalic acid (H2BDC) as organic ligand and Ce as active metal center.The as-prepared Ce-BDC was well characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS).Then the oxidase-like activity of Ce-BDC was revealed and Ce-BDC could catalyze the colorless 3,3,5,5-tetramethylbenzidine(TMB) to produce a deep blue oxidation product oxTMB which has a strong UV absorption peak at 652 nm.The catalytic activity of Ce-BDC follows the Michaelis-Menten kinetics,which could be affected by pH value and temperature condition.Results showed that the optimal reaction temperature is 30 ℃,the optimal reaction pH value is 3.0,and the optimal reaction time is 120 s.Due to the strong reducing property of ascorbic acid,the addition of ascorbic acid could reduce oxTMB into colourless TMB,resulting in the fading of blue color and the decrease of absorbance at 652 nm.Based on this phenomenon,a colorimetric method was established for ascorbic acid detection.Under the optimum reaction conditions,the absorbance of the reaction solution at 652 nm has a good linear relationship with the concentration of ascorbic acid in the range of 1.0-30 μmol/L,and the detection limit for ascorbic acid was found to be 0.32 μmol/L,which could satisfy the requirements for the practical detection of ascorbic acid.The established method was applied in the detection of ascorbic acid in fruit juice sample via standard addition test.The recovery for ascorbic acid was in the range of 98.2%-102%,with the relative standard deviations of 1.2%-7.2%,demonstrating that the method is promising for the rapid and selective detection of ascorbic acid.In a word,this work provides a new approach for the colorimetric detection of ascorbic acid in fruit juice based on nanozyme.