Design Of Nanozyme-based Colorimetric Sensors And Their Application In Detecting Phenolic Pollutants In Drinking Water

With the progress of technology and the development of society,the quality of human life has been gradually improved,and the food safety issue has drawn much attention.The sources of pollutants in food mainly include two types:endogenous pollution and exogenous pollution.And the phenolic pollutants,acting as one of the most harmful pollutants to human body in exogenous pollution,have gradually stepped into public view.Phenolic pollutants are widely applied in the production of industry and agriculture.Due to improper treatment and discharge,surface water can be easily polluted and then phenolic pollutants will enrich through the food chain,which eventually endanger the health of animals and human beings.And most of drinking water in daily life use surface water as raw water,and are obtained after purification treatment.Therefore,it is of vital significance for the detection of phenolic pollutants in drinking water.Currently,various nanosized materials have been explored as enzyme mimics,and they possess intrinsic enzyme-like features（nanozymes）.Compared with natural enzymes,nanozymes,which exhibit advantages of better stability and lower cost,have attracted wide interest of researchers.So far,lots of nanozymes have been employed for mimicking a variety of natural enzymes,including oxidase-like nanozyme,peroxidase-like nanozyme and catalase-like nanozyme.The enzyme-like catalytic properties make these nanozymes widely applied in biochemical detection,environmental protection,and biomedicine.Although nanozymes exhibit the superiorities of high stability,low price and easy preparation,there are still some deficiencies such as low catalytic activity and poor selectivity,which should be further improved.With the above considerations,in this thesis we designed several colorimetric sensors and arrays by rationally regulating the catalytic activity of nanozymes,and we further applied these sensors and arrays in the detection of typical phenolic pollutants in drinking water.1.Fe₃O₄ nanoparticles（Fe₃O₄ NPs）with a 11 nm size were prepared by a coprecipitation method,and their peroxidase-like feature was investigated.Further,a simple and efficient colorimetric sensor was fabricated for the colorimetric detection of phenol by using Fe₃O₄ NPs as a peroxidase mimic.The results indicate that the prepared small-sized Fe₃O₄ NPs exhibit high peroxidase-like activity to catalyze the oxidative coupling of phenolic species and 4-aminoantipyrine（4-AAP）in the presence of H₂O₂,making it possible for the rapid visual detection of the analyte.The fabricated colorimetric sensor can realize the sensitive detection of phenol,giving a detection range from 1.67μM to 1.2 mM and the limit of detection（LOD）is determined to be 3.79μM.The colorimetric sensor can be successfully applied to the quantitative detection of phenol in drinking water samples.2.In real samples,various phenolic pollutants usually exist simultaneously,while these pollutants tend to have different bio-toxicities and environmental effects.Therefore,it is essential to detect and identify different phenolic pollutants.Based on Fe₃O₄ NPs with peroxidase-like catalytic activity,we proposed a colorimetric sensor array for the rapid discrimination of phenolic compounds in drinking water.The sensor array possesses different reaction kinetics towards different phenolic pollutants.With the array,common phenolic pollutants（phenol,chlorophenol,aminophenol and nitrophenol）can be well differentiated even at a very low concentration.The results show that the fabricated colorimetric sensor array can correctly discriminate various phenolic pollutants.The sensor array can even accurately identify different phenolic pollutants in actual samples.3.Fe₃O₄@MnO_x was prepared by growing oxidase-like MnO_x nanoflakes on the surface of magnetic Fe3O4 particles via a hydrothermal process.The proposed Fe3O4@MnO_x acted as an oxidase mimic.Further,we reported a recyclable colorimetric sensor array based on the oxidase-mimicking catalytic characteristics of Fe3O4@MnO_x for the high-performance quantification and differentiation of typical chlorophenols（CPs）.The results show that the fabricated sensor array can successfully realize the high-sensitivity detection of o-chlorophenol,giving the linear detection range of 0.1–1600μM,and the limit of detection（LOD）is determined as low as 0.85μM according to S/N=3.By combining the array with principal component analysis（PCA）and hierarchical clustering analysis（HCA）,chlorophenol pollutants can be well identified,providing a 100%identification accuracy.