Colorimetric Method For Detection Of Glucose By MOFs Encapsulated Enzyme

Glucose is widely applied to the food processing industry,so the content of glucose has become an important detection index for judging the texture and flavor of food in the production process of candy,cakes,health products,dairy products and beverages.The measurement of glucose is very important for the study of human health and food safety.Although traditional glucose detection methods are relatively mature,it is difficult to achieve rapid and sensitive monitoring due to their high cost,low sensitivity,and complicated operation.Therefore,it is of great commercial value and scientific research significance to develop new cost-efficient alternative and stable nano materials for colorimetric biosensors to achieve real-time,fast and convenient detection of glucose content.In order to improve the stability of enzymes,the integration of enzymes into metal organic frameworks（MOFs）as guest species has been widely used in industrial catalysis,sensing and medical instruments.It has been reported that different kinds of macroporous MOFs are used as the outer shell of the enzyme.Enzymes play an important role both inside and outside the organism.Although the enzyme has high catalytic activity and specificity,the survival conditions of the enzyme are more stringent,and the enzyme will be inactivated and decomposed at a faster speed when exposed to room temperature or higher temperature for a long time.Therefore,it is of great research significance to study whether mimic enzymes can replace natural enzymes to form a cascade nanoreactor to determine glucose.So this paper is based on MOFs,the sensor is constructed to detect glucose quickly,sensitively and in real time by colorimetry.The experiment is mainly composed of the following two parts:（1）In this work,glucose oxidase（GOx）and Au nanoclusters（AuNCs）co-encapsulated in zeolitic imidazolate frameworks（GOx&AuNCs@ZIF-8）were obtained by simply mixing Zn²⁺,dimethylimidazole,glucose oxidase and Au nanoclusters at room temperature.The GOx&AuNCs@ZIF-8 composite can be used as a sensitive colorimetric sensor for glucose based on the following cascade reaction:GOx converts glucose to gluconic acid and generates H₂O₂,which acts as a substrate for AuNCs oxidizing 3,3’,5,5’-tetramethylbenzidine（TMB）to form oxidized TMB（ox TMB）detectable at 652 nm.Owing to the effective cascade reaction and protective effect of the ZIF-8 shell on enzymes,the catalytic activity of GOx&AuNCs@ZIF-8 was enhanced 19.3-fold compared with the free GOx/AuNCs solution,and the glucose sensor showed high selectivity and sensitivity.Furthermore,the GOx&AuNCs@ZIF-8 composite showed high long-term storage stability against digesting enzymes and chelating compounds due to the shielding effect of the ZIF-8 scaffold.（2）An integrated system was obtained from a HKUST-1 and glucose oxidase for one-step cascade determination of glucose by the co-precipitation method.Herein,GOx@HKUST-1 performed dual functions of shell that protected glucose oxidase and replaced horseradish peroxidase.In the GOx@HKUST-1 composite,glucose can be converted to gluconic acid and H₂O₂.In the presence of HKUST-1 peroxidases,hydrogen peroxide was used as an intermediate product,and it was immediately converted to·OH to oxidize 3,3’,5,5’-tetramethylbenzidine at 652 nm.The absorbance at 652 nm was observed using the UV-Vis spectra.Based on the above principles,the GOx@HKUST-1 composite was characterized by SEM,XRD,FT-IR,UV-Vis,EDS,etc.,to prove that the enzyme was successfully encapsulated.In addition,The glucose concentration was positively and linearly correlated with absorbance in the range 0.5-20μM with a detection limit of 0.4μM.At the same time,the effects of pH and temperature were explored,the selectivity of the sensor system was evaluated,and longterm stability and stability against trypsin or EDTA of the GOx@HKUST-1 composite were studied.This strategy had the characteristics of high precision,convenient operation and biological application.The colorimetric sensor had been successfully applied to the detection of glucose in food,providing a more convenient and sensitive operating platform for food quality analysis.