Functional Regulation And Analytical Application Of Fluorescent Carbon Dots

Carbon dots(CDs),as a new type of fluorescent nanomaterials,have attracted tremendous attention due to their adjustable fluorescence characteristics,excellent biocompatibility,high photostability and easy surface modification.At present,analysis detection of fluorescent CDs are mostly single-function and single-mode detection.Therefore,in our work,we developed rational strategies for the synthesized of functionalized CDs and regulated its fluorescence properties.Based on this,four kinds of fluorescent CDs with excellent properties were designed and prepared for multi-functional and multi-mode fluorescence analysis.Chapter 1:The structure,preparation method,optical properties and luminescent mechanism of CDs were briefly described.On this basis,we reviewed the regulation of fluorescence properties,and the research progress of CDs in the fields of fluorescence sensing,biological imaging,disease diagnosis,and anti-counterfeiting.Chapter 2:Excitation-independent functionalized fluorescent CDs were prepared by one-step hydrothermal method using salicylic acid as carbon source.The structure and properties of the CDs were studied in detail.Due to the interaction between Fe³⁺and the surface functional groups of CDs,the fluorescence of CDs was extinguished dramatically and subsequently recovered upon addition of F^-owing to the formation of stabler complexes.Based on the mechanism,“on-off-on”fluorescence sensor was constructed for sequential detection of Fe³⁺and F^-,with detection limits of 52 n M and 8.5 n M,respectively.More importantly,as-prepared CDs with exceedingly fluorescence stability,negligible toxicity and superior biocompatibility have been expanded for detection Fe³⁺and F^-in living cell and Escherichia coli.In addition,an"AND"logic gate is designed based on the fluorescence changes of CDs.Compared with the single signal output mode,this analysis strategy will have a good prospect in practical application.Chapter 3:Yellow-fluorescent nitrogen-doped carbon dots(Y-CDs)were synthesized hydrothermally using 4-aminosalicylic acid as a single raw material.After analysis of their morphology,structure and luminescent properties,as-prepared Y-CDs exhibited exceptional advantages including unique excitation-independent emission,superior biocompatibility,low toxicity,and satisfactory optical stability.Depending on these eminent properties,the Y-CDs have been utilized for intracellular Al³⁺imaging and paper-based Al³⁺sensing.They could image Al³⁺fluctuations in living cells without interference of auto-fluorescence based on their high selectivity and sensitivity detection for Al³⁺ions in aqueous solution with a good linearity in the concentration range of 10–200?M and 225–400?M and a detection limit of 1.69?M.Moreover,a paper-based sensor strip containing Y-CDs has been prepared for Al³⁺sensing,which provides a convenient and user-friendly approach for the visual detection of Al³⁺.Chapter 4:Nitrogen and phosphorus co-doped red fluorescent carbon dots(R-CDs)were fabricated via one-pot hydrothermal method using neutral red and thiourea as precursors.As-obtained R-CDs possess excellent photobleaching resistance,good photostability and biocompatibility.Importantly,the?-?interaction between tetracycline antibiotics(TCs)and R-CDs enhanced the fluorescence of R-CDs significantly.Based on this,an aggregation induced enhanced sensor was constructed to detect TCs.The proposed method has been successfully applied to the analysis of TCs in milk products.Furthermore,the R-CDs exhibited a distinct H⁺-sensitive feature,and have been used to construct fluorescent p H sensor in linear range of 6.0–8.0 with a p Ka of 7.08.Notably,the nanosensor has been also extended to monitor TCs and p H in cellular systems,demonstrating the proposed methodology presents promising biosensing application prospect.Chapter 5:Double emission fluorescent carbon dots were synthesized by simple hydrothermal method selecting alizarin red as carbon source,manifesting intriguing dual-emission behavior at 430 and642 nm.Based on the reduction of glutathione(GSH)with disulfide bond of CDs,a dual-mode ratio sensor was designed for direct detection of GSH,which effectively eliminate the background interference and improve the detection accuracy.With the increase in GSH concentration,the fluorescence intensity ratio of I₄₃₀/I₆₄₂increased with good linearity in the range 1-10 to 25-150?M and the detection limit of 0.26?M.More importantly,confocal fluorescent imaging of cancer cells and normal cells indicated that obtained CDs could be implemented as an effective tool to visualize cancer cells with overexpressing GSH.