▎ 摘　　要

A new off-on fluorescent probe was successfully synthesized and used to detect ascorbic acid and phytase. The composite material of hydrotalcite and graphene quantum dots were synthesized through citrate intercalated hydrotalcite using hydrothermal carbonization method. The layered structure of hydrotalcite can prevent the aggregation and promote the uniformity of graphene quantum dots. The off-on fluorescent probe detection mechanism is as follows. Fe3+ ions were firstly added into the solution of the composite material, and the fluorescence was quenched. Then, ascorbic acid was added into the fluorescence probe system, which reduced iron ions and turned on fluorescence to realize the detection of ascorbic acid. In addition, the reaction of phytase and L-ascorbyl-2-phosphate can produce ascorbic acid, further achieving the purpose of phytase detection. The concentration of the analyte and the recovery of the fluorescence intensity show a linear relationship, the linear ranges were 5-300 mu mol L-1 and 0.1-4 U mL-1 for ascorbic acid and phytase, respectively. The recoveries of the experiment were 96.3 %-103.1 % and 95.4 %-104.9 %, respectively. The fluorescence method has the advantages of fast, stable, high sensitivity and high selectivity, which has been successfully applied to the determination of ascorbic acid in fruit juice and phytase in feed.