Construction And Application Of Biosensing Platform Based On Fluorescent Carbon Quantum Dots

Enzymes,as important biological catalysts,can widely promote various biosynthesis in biological tissues to maintain various physiological functions under extremely mild conditions.Bioenzymes are essential for maintaining the normal body functions of organisms and are considered as important biomarkers in clinical diagnosis.Therefore,accurate and quantitative detection of enzyme activity in organisms is beneficial to biological research and evaluation of therapeutic effects of diseases.The fluorescent detection strategies for biological enzymes based on fluorescent probes usually have the advantages of low cost,real-time detection,good specificity,and biological Good compatibility and so on.As one of the important members of the carbon-based material family,carbon quantum dots(CQDs)not only have similar physicochemical properties to the representative carbon-based materials,but also do not contain heavy metal elements.Carbon quantum dots(CQDs)has the advantages of adjustable band gap,low cytotoxicity and stable photoluminescence.Carbon quantum dots possess powerful functional groups with excellent optical and biological properties,and the process of modifying carbon quantum dots allows the detection and attachment of various specific analytes on their surfaces through electrostatic interactions and hydrogen bonds,so it has shown great potential in practical clinical biomedicine disease diagnosis,fluorescence detection of bio-enzyme and cell imaging.In this paper,carbon quantum dots with different fluorescence properties were prepared as fluorescent probes.Based on the excellent fluorescence properties of our prepared carbon quantum dots,a variety of effective and novel fluorescent biosensing platforms for detecting biological enzyme activities have been constructed.And it has been effectively confirmed that the constructed fluorescence detection platform still exhibits good analytical detection performance in actual biological samples.The specific research contents are as follows:In the first chapter,we briefly outline the basic morphology,structure and development process of carbon quantum dots,summarize various common methods for preparing carbon quantum dots,and then systematically discuss the optical properties,modification methods and biological applications of carbon quantum dots.Finally,the design ideas of this paper are systematically described,and the research significance of biological enzyme detection experiments is discussed.In the second chapter,we established a novel and ultrasensitive dual-signal fluorescence emission detection system of protamine and trypsin based on the electrostatic interaction between polyethyleneimine(PEI)surface-modified positively charged carbon quantum dots(CDs-PEI)and anionic fluorescent dye Eosin Y.As a cationic peptide,protamine can quench the yellow-green fluorescence of Eosin Y at 542 nm through electrostatic interaction.In the presence of trypsin,protamine could be specifically hydrolyzed by trypsin,which led to the subsequent recovery of the fluorescence of Eosin Y.Simultaneously,the blue fluorescence emission of CDs-PEI at 452 nm remained constant during the whole process.Hence,a ratiometric fluorescent nanoprobe for protamine and trypsin detection with high sensitivity was successfully constructed based on CDs-PEI and Eosin Y.For protamine detection,the ratiometric fluorescence intensity(I₅₄₂/I₄₅₂)exhibited an excellent linear relationship in the range from 0.1 to 5.2?g/m L with a detection limit(LOD)of 0.03?g/m L.And the linear relation between I₅₄₂/I₄₅₂ and trypsin concentration ranged from 0.4-56 ng/m L with the LOD of 0.21ng/m L.By evaluating the performance of this method in the detection of trypsin in actual human urine samples,satisfactory results were finally obtained.In the third chapter,we prepared Co,N co-doped porous carbon-based nanozymes(Co-N-C nanozymes).Taking advantage of the excellent oxidase catalytic activity and remarkable stability of Co,N co-doped carbon-based nanozymes,we propose a novel method based on Co,N co-doped porous hybrid carbon-based nanozymes(Co,N co-doped carbon-based nanozymes).A dual-signal fluorescence colorimetric system of carbon-based nanozymes)and red-emitting carbon quantum dots(RCDs)for high-sensitivity butyrylcholinesterase(BCh E)sensing.Since the chromogenic substrate 3,3',5,5'-tetramethylbenzidine(TMB)was catalyzed by Co,N co-doped carbon-based nanozymes,and produced a new UV absorption peak at 652nm,This results in significant quenching of carbon quantum dot fluorescence at 610 nm.Under the catalysis of BCh E,S-butyryl iodide thiocholine(BCh)is hydrolyzed to form thiocholine,and the generated thiocholine effectively inhibits the oxidation of TMB catalyzed by Co and N co-doped carbon-based nanozymes,resulting in Reduced UV absorption of ox TMB at 652 nm and efficient fluorescence recovery of RCDs.Both the fluorescence and colorimetric dual-signal systems exhibited excellent linear responses to BCh E activity in the range of 0.5-40 U L^-1,with LODs of 0.21 U L^-1 and 0.16 U L^-1 for the fluorescence and UV detection methods,respectively.Furthermore,this established two-channel biosensing strategy has been successfully used for the measurement of BCh E in human serum samples with satisfactory recovery,effectively expanding the development and application of nanozymes in biosensing.