Synthesis Of Mercapto-Functionalized Carbon Dots For Applications In Fluorescent Detection Of Biomarkers

The most effective way of disease prevention and control is early detection and early treatment.Clinical diagnostic methods,including B-ultrasound,CT,and nuclear magnetic technology,are difficult to achieve the purpose of early detection.Highly sensitive detection of biomarkers is an effective way for early diagnosis of diseases.Fluorescence biosensors have received extensive attention because of their high sensitivity,wide detection range,and simple operation.For fluorescent biosensors,the selection and optimization of fluorescent probes are extremely important.Carbon dots have become an efficient fluorescent sensing material due to their small size,good biocompatibility,and adjustable optical properties,and have important application values in the field of biosensing.In this dissertation,new mercapto-functionalized carbon dots were synthesized for the construction of fluorescent biosensors for simple,rapid and sensitive detection of multiple biomarkers.The main contents are listed as follows:（I）This dissertation briefly introduces some common biosensor types and analyzed their advantages and disadvantages.Then,fluorescent biosensors and the sensors with carbon dots as signal probes were introduced.Moreover,the applications of carbon dots-based sensors in the detection of heavy metal ions,biological small molecules,proteins and nucleic acids were discussed in detail.（II）Carbon dots with yellow-green light were prepared by hydrothermal reaction with malic acid as carbon source,and then the mercapto-functionalized carbon dots（S-CDs）were prepared by covalent bonding with mercaptopropylamine as modifier with excellent stability and good water dispersion.S-CDs exhibited excellent response to H₂O₂:After exposure to H₂O₂,S-CDs were transformed into nonluminous S-CDs assembly based on target-initiated catalyzed oxidation of–SH into–S–S–.Based on the response of S-CDs to H₂O₂,glucose oxidase catalyzes the hydrolysis of glucose to form H₂O₂.S-CDs were used as a signal probe to achieve high sensitivity detection of glucose.The detection range of this method is 0.1-1000μM,and the detection limit is0.03μM.It was further applied to the determination of glucose in human serum,and the results were consistent with those of commercial instruments.（III）Based on target-induced strand displaced amplification（SDA）,the mercapto-functionalized carbon dots（S-CDs）were used as a fluorescent signal probe.A fluorescence sensor for miRNA detection was constructed.S-CDs were employed to detect miRNA,using miRNA-21 as target model,which triggered the SDA reaction of P1 and P2 to generate hemin/G-quadruplex,subsequently making S-CDs transform from dot to aggresome along with the quenched fluorescence.Hemin/G-quadruplex catalyzed the oxidation of–SH to form–S–S–with the assistance of H₂O₂.Then,the S-CDs gather to quench the fluorescence.Based on the change of fluorescence intensity before and after miRNA addition,it can realize its sensitivity and selectivity detection.The detection range of this method is 0.1 p M-100 p M,and the detection limit is 0.03 p M.（IV）In ordert to improve the sensitivity detection of miRNA,a fluorescence sensor for high sensitive detection of miRNA was constructed based on the catalytic oxidation and internal filtration effects initiated by the target.When the target is present,the target triggers a hairpin DNA（P1,P2）SDA amplification reaction to generate a large number of hemin/G-quadruplex.Hemin/G-quadruplex catalyzed the oxidation of–SH to form–S–S–.The aggregation of S-CDs could quench the fluorescence signal.At the same time,hemin/G-quadruplex could oxidize dopamine to produce dopamine quinone,and the internal filtration effect was induced to further reduce the fluorescence intensity of the system.The sensitive and selective detection of target can be realized based on the change of fluorescence intensity before and after the addition of miRNA.