Preparation Of Julolidine-derived Carbon Dots And Their Applications In Nucleic Acid-related Senescent Cell Monitoring And Photocatalytic Antibacteria

As a novel kind of zero-dimensional carbon-based nanomaterial,carbon dots have been widely applied in biosensing,bioimaging,and photocatalysis due to their features like great biocompatibility,low cytotoxicity and excellent optical properties.Recently,carbon dots(CDs)have been found to display specific responsiveness to several biomolecules and cellular organelles.However,the application range of these CDs is confined to the identification of cancer cell.In this thesis,with the intention of extending the application scope and strengthening the depth of application,we aim to develop DNA-responsive carbon dots and probe their application potentials in early monitoring of senescent cells and photocatalytic antibacterial field by combining the fluorescence and photocatalytic properties,respectively.The two major areas include the following.1 DNA-response carbon dots as fluorescent tracer for the monitoring of senescent cellsA kind of novel CDs was prepared by microwave method with julolidine and citric acid as precursors.The fluorescence of CDs was enhanced after binding with nucleic acids in extracellular and intracellular experiments,suggesting that the CDs possessed RNA-response feature.In the cell imaging experiments,the CDs were found to be enriched only on the cell membranes of senescent cells.Such enrichment phenomenon disappeared when the senescent cells was previously incubated with RNA enzyme.We can deduce that the RNA abundance on the cell membrane of senescent cells was increased,which caused an enhanced fluorescence of RNAresponse CDs.Based on above enrichment phenomenon,a RNA-mediated cellular senescence monitoring method was established using CDs as fluorescent tracer.Unlike conventional method that distinguishes cellular senescence by assessing lysosomal β-galactosidase activity,this developed strategy allows for earlier and faster monitoring of cellular senescence.2 DNA-response and positively-charged carbon dots as dual-model photocatalytic agent for improving antibacterial performanceBy integrating 8-hydroxyjulolidine with abundant electron donors and acceptors into aforementioned precursors,a novel type of red fluorescent CDs was prepared by microwave method.It was shown that the fluorescence intensity of CDs decreased after binding to DNA/RNA,reflecting that the CDs retained the DNA-response feature.Furthermore,the carbon dots display the ability to catalyze oxygen for the generation of hydroxyl radicals under light.CDs displayed excellent lethality under light illumination when using as photocatalytic antibacterial agent.The results from gel electrophoresis and SEM analysis confirmed that the DNA structure and cell membrane of bacterial cells had been damaged during the antibacterial experiment.Since the carbon dots were demonstrated to be charged positively by Zeta potential analysis,we inferred that the carbon dots were firstly absorbed onto the negativelycharged cell membrane.After that,some of CDs gradually penetrated into the bacteria and bound with DNA due to their DNA-response feature.Meanwhile,the residual CDs still located on the cell membrane.In this case,the hydroxyl radicals generated by CDs under light illumination simultaneously break the DNA structure and cell membrane of the bacteria to achieve the dual-channel antibacterial mode,which opens a new way to design of high-performance antibacterial agents.