Research On New Detection Method Of Curcumin And Oxytetracycline Based On Sulfur Quantum Dots

Sulfur quantum dots（SQDs）,as a new class of metal-free fluorescent quantum dots,can be directly synthesized from the cheap and abundant element S.It has received special attention in the fields of bioimaging and biosensing because of its good biocompatibility,low toxicity,and unique surface properties.Quantum dots（QDs）can react with biomacromolecules,potentially causing unwanted negative effects on biological systems.Therefore,it is very important to explore the interactions between SQDs and biomacromolecules.Food additives,antibiotic residues,etc.will directly or indirectly pollute the environment and eventually endanger human health.Therefore,it is of great significance to accurately detect the content of these substances.In this paper,PEG-SQDs were synthesized to study the interaction between SQDs and BSA and to construct a ratiometric fluorescent probe for the detection of curcumin（Cur）;at the same time,PEI-SQDs were synthesized for the first time to construct a ratiometric fluorescent sensor for the detection of OTC.system.The main research contents are as follows:1.Using bovine serum albumin（BSA）as a model protein,its interaction with SQDs was studied by multispectral techniques.First,SQDs can effectively quench BSA fluorescence,and the quenching mode is confirmed to be dynamic.In addition,the thermodynamic parametersΔG,ΔH,andΔS were also obtained and demonstrated that the hydrophobic interaction plays a key role in the spontaneous interaction.Binding constants(Ksv≈10³ mol^-1 L^-1)and binding sites（n≈1）were calculated.In addition,the results of ultraviolet-visible absorption spectroscopy（UV-Vis）,circular dichroism（CD）,Fourier transform infrared（FT-IR）,and synchronous fluorescence spectroscopy（SFS）revealed the conformational changes of BSA.This study contributes to the understanding of the biotoxicity of SQDs to biomolecules and their potential applications in the field of biosensing.2.In this section,a ratiometric fluorescent sensor is developed to achieve fast and sensitive detection of Cur with SQDs for the first time.PEG-SQDs were synthesized by H₂O₂ assisted surface etching method with sulfur powder as sulfur source and PEG-400（Polyethylene glycol 400）as capping agent.Based on the principle of fluorescence resonance energy transfer（FRET）,a fast and simple ratiometric fluorescent sensing system was constructed.Cur can quench the blue fluorescence of SQDs through fluorescence resonance energy transfer,while the yellow fluorescence of Cur itself at525 nm is further enhanced.Using F₅₂₅/F₄₄₃ as the ordinate and the concentration of Cur as the abscissa to carry out linear fitting,the results show that the ratio of F₅₂₅/F₄₄₃has a good linear relationship with the concentration of Cur in the range of 0 to 20.00μmol/L,and the detection limit is as low as 30 nmol/L.In addition,the detection of Cur in food samples curry powder and turmeric powder was successfully realized through the standard recovery experiment.3.In this chapter,using sulfur powder as the sulfur source,PEI-600（polyethyleneimine 600）as the capping agent,and NaClO as the etchant,the PEI-SQDs were synthesized for the first time,and the SQDs-Eu³⁺ratiometric fluorescence sensor was designed and developed to quickly and sensitively monitor OTC.Based on the internal filter effect（IFE）and"antenna effect"（AE）,a proportional fluorescence dual emission signal fluorescence sensor is constructed.OTC quenches the blue fluorescence of SQDs through the IFE effect,and at the same time enhances the Eu³⁺red fluorescence through the AE effect to achieve the ratio to OTC.Fluorescent detection.Using F₆₂₃/F₄₃₈ as the ordinate and the concentration of OTC as the abscissa to carry out linear fitting,the results show that the fluorescence ratio of the system at F₆₂₃/F₄₃₈ and the OTC concentration are within the two ranges of 0～20.00 and 20.00～100.0μmol/L.Good linear relationship,the detection limit is 0.014μmol/L.In addition,a portable,low-cost smartphone-assisted paper-based sensing platform was developed to realize the visual quantitative analysis of OTC.