Fluorescence Detection And Application Of N-Acetyl-β-D-Glucosaminidase And Tetracycline Based On Sulfur Dots

Sulfur quantum dots（SQDs）has potential application value in the detection of biological macromolecules and drug molecules because of its low cytotoxicity,good biocompatibility,excellent water dispersibility,light stability,adjustable size and luminescence.Enzymes as active substances in living organisms,changes of its content may be closely related to the development and changes of some diseases.Antibiotics as drugs to inhibit or treat microbial infections,are abused in animal feeding,which leads to antibiotic residues in animals,and then leads to a series of environmental problems and human health problems.Therefore,the detection of enzyme activity and antibiotic content is closely related to human health.Based on the synthesis of SQDs modified by polyethylene glycol-400（PEG-400）and modified by carboxymethyl cellulose（CMC）,fluorescent probe was constructed for the detection of N-acetyl-β-D-glucosaminidase（NAG）and tetracycline（TC）.The specific research is as follows:1.Sulfur powder and sodium hydroxide were used as raw materials to synthesis SQDs with PEG-400 modification and H₂O₂-assisted etching,through a top-down approach.The morphology,optical properties,surface elements of SQDs were analyzed by transmission electron microscopy（TEM）,ultraviolet-visible light（UV-Vis）spectroscopy,fluorescence spectroscopy,fourier transform infrared（FT-IR）spectroscopy,x-ray photoelectron energy spectroscopy（XPS）and other means.Taking the mixed solution of SQDs and p-Nitrophenyl-N-acetyl-β-D-glucosaminide（PNP-NAG）as the detection system,according to inner filter effect（IFE）,the fluorescence of SQDs can be quenched by p-Nitrophenol（PNP）produced by NAG’s catalytic hydrolysis of PNP-NAG,so the activity of NAG was successfully determined according to the quenching degree of the fluorescence of SQDs.The activity of NAG has a good linear relationship with the fluorescence quenching degree of SQDs from 0.4 to 7.5 U/L,and the limit of detection is as low as 0.1 U/L,which has high sensitivity.In addition,adding interfering substances to the system showed a negligible effect on the detection of NAG,indicating that the method has good specificity.Furthermore,the detection system was successfully used in the detection of NAG activity in bovine serum and human urine samples by the spike recovery test,which proves that the method proposed in this paper has a low detection limit and is expected to be used for highly sensitive detection of NAG activity in clinic.2.SQDs modified by CMC were synthesized by a top-down method using sulfur powder and sodium hydroxide as raw materials.Eu（NO₃）₃·6H₂O and cytidine monophosphate（CMP）were used as raw materials to synthesis Eu/CMP coordination polymers（Eu/CMP CPNs）with spatial network structure by self-assembly.The morphology and optical properties of the two materials were characterized by TEM,UV-Vis,fluorescence spectroscopy,FT-IR and other means.SQDs,Eu/CMP CPNs,and citric acid（cit）were mixed to construct SQDs-Eu/CMP-cit ratio fluorescence probe for the detection of TC content,through the different response of TC to the fluorescence signals of SQDs and Eu³⁺at different wavelengths.The content of TC has a good linear relationship with the fluorescence ratio at 618 and 440 nm from 0.05 to 15.00μmol/L,and the limit of detection is 25 nmol/L,which has high sensitivity.Adding interfering substances to the system,except for ciprofloxacin,the interfering substances all show negligible effects on the detection of TC,indicating that the method has good specificity.Furthermore,the detection of TC content in actual samples of milk,pork and pork liver was realized by the spike recovery test.The above results show that the SQDs-Eu/CMP-cit ratio fluorescence probe has a good ability in the detection of TC content,and does not require complex instruments and large costs.Thus it is expected to be used for the rapid detection of TC residues in animal-derived foods.