Construction Of Fluorescent Probes Based On Carbon Quantum Dots And Their Applications In The Detection Of Heavy Metal And Mycotoxin

The contamination of heavy metals and mycotoxins has raised concerns in the fields of environmental monitoring,food safety,and biomedicine.Improving the level of detection technology and timely monitoring and discovery of these hidden dangers are crucial.In this study,heavy metals and mycotoxins are chosen as the detection targets,and the research on carbon dot synthesis and detection methods is primarily reflected in two aspects.Firstly,an appropriate carbon source is selected,and the dopants are adjusted.By doping carbon dots with different elements or modifying its surface functional groups,their fluorescence properties are optimized and regulated.Secondly,nano-materials with excellent performance,including cobalt hydroxide and molybdenum disulfide nanosheets,are introduced to construct quenching,enhancing,and recovery fluorescence sensing systems,thereby achieving the simultaneous detection of trace heavy metals and mycotoxins in grains.The main results are as follows:1.Preparation and application of blue carbon quantum dots for the quenching detection of Hg²⁺.Nitrogen-sulfur co-doped and nitrogen-doped carbon quantum dots were synthesized through a one-step hydrothermal method using polyvinylimine and cysteine,sodium citrate,and polyacrylamide as precursors.The quantum yield of nitrogen-doped carbon quantum dots is 38.9%,surpassing that of nitrogen-sulfur co-doped carbon quantum dots（16.4%）.Nitrogen-doped carbon quantum dots exhibit good selectivity for Hg²⁺and are not interfered with by other ions.The detection limits for Hg²⁺using nitrogen-sulfur co-doped and nitrogen-doped carbon quantum dots are1.84 ng/m L and 0.26 ng/m L,respectively.When applied to water and rice samples,the recovery rates for nitrogen and sulfur co-doped,and nitrogen-doped carbon quantum dots are 92%～104%and 90%～98.6%,respectively,demonstrating their reliability and accuracy in the detection of Hg²⁺in real samples.2.Preparation and application of blue carbon quantum dots for enhanced detection of patulin.Nitrogen-doped carbon quantum dots were synthesized using citric acid and ammonia as precursors.Through surface modification,a sulfhydryl group was introduced to the surface of carbon quantum dots,resulting in the construction of sulfhydryl-functionalized carbon quantum dots.The carbon quantum dots before modification exhibited no fluorescence response to patulin,whereas the modified sulfhydryl-functionalized carbon quantum dots displayed a fluorescence enhancement response to patulin,with the enhancement being approximately 2.5 times.There was no fluorescence response to four other possible co-occurring mycotoxins（aflatoxin B1,ochratoxin A,zearalenone,and vomitoxin）.The detection limit of thiol-functionalized carbon quantum dots was as low as 0.053 ng/m L within the linear range of 0.1～400ng/m L.Standard recoveries were 88.9%-99.2%and 92.5%-101.8%for the determination of patulin in apple juice and grape juice,respectively.3.Construction of a restorative red fluorescent probe and its application in ochratoxin detection.Red fluorescent carbon quantum dots（λem=658 nm）were synthesized from natural rosemary leaves using the hydrothermal method.At a concentration of 0.2μg/m L for cobalt hydroxide nanosheets,the fluorescence quenching efficiency of red fluorescent carbon quantum dots reached approximately87%.Based on the response of the aptamer and target,along with enzyme-induced fluorescence recovery of red fluorescent carbon quantum dots,a restorative fluorescence detection method for ochratoxin was established.In the linear range of 1-100 ng/m L,the detection limit for ochratoxin was as low as 0.7 ng/m L,and this limit was not interfered with by the other five mycotoxins（aflatoxin B1,tricillin,zearalenone,and citricillin）.The recovery rates of ochratoxin in wheat and rice were 88.9%-99.2%and 92.5%-101.8%,respectively.4.Construction and application of a three-color fluorescent carbon quantum dot sensing system for the simultaneous detection of Hg²⁺,ochratoxin,and patulin.Utilizing synthetically prepared blue,red,and yellow carbon quantum dots,a three-color sensing system was established for simultaneous detection of Hg²⁺,ochratoxin,and patulin.Aptamer was employed as the surface functional identification probe,and molybdenum disulfide nanoparticles served as the adsorption substrate.Under the same excitation wavelength,the emission peaks of the three carbon quantum dots were separated and did not interfere with each other.The sensor system exhibited no interference from other heavy metal ions and mycotoxins when detecting Hg²⁺,ochratoxin A,and patulin.The detection ranges were 1～200,0.1～50,and 0.1～100ng/m L,with detection limits of 0.84,0.01,and 0.3 ng/m L,respectively—all lower than national limit standards.In wheat and rice samples,recoveries fell within the range of91.0%～101.2%,meeting the accuracy requirements of the method.It was confirmed that matrix effects existed in actual sample detection,and the fluorescence enhancement of glutenin was positively correlated with protein concentration.The interaction between glutenin and carbon dots was analyzed.The results of this paper will provide a general sensing strategy for multichannel analysis,characterized by good selectivity and high sensitivity,with broad application prospects in food quality control and other aptamer-related fields.