The Synthesis Of Functionalized Fluorescent Carbon Dots And Their Applications In The Detection Of Heavy Metal Ion And Cell Imaging

Compared with the common fluorescent dyes,luminescent nanomaterials show excellent photostability,chemical inertia,favourable biocompatibility.The nanomaterials have also unique advantages,such as small size effects,dielectric confined effect and macroscopic quantum tunneling effect.The luminescent nanomaterials can play more meaningful roles in the fields including physics,chemistry,biology,medicine and environment.In recent years,nanomaterials with luminescent properties have attracted increasing attention and have been exploited in the fields of chemical sensing,biomarker,drug delivery,optical elements and photocatalysis.As an important new member of luminescent nanomaterials,the fluorescent carbon dots(CDs)have become a hot research topic because of its good biocompatibility,low cytotoxicity,excellent optical properties and chemical stability.Many researchers have done a lot of works on the innovation of preparation methods,the control of luminescent properties,and the exploration of luminescence mechanisms.On the basis of the work of predecessors,we started with the design and synthesis of functionalized CDs in this dissertation.The CDs were prepared by optimizing the reaction material and the preparation method for the detection of heavy metal ion and cell imaging.Furthermore,a new method to control the emission wavelength of CDs was proposed and the synthesized CDs was used for multi-color cell imaging.The dissertation consists of four chapters.Chapter one: On the basis of a large number of literature,the development background of luminescent nanomaterials was summarized.The properties,photoluminescent mechanisms,preparation methods and applications of fluorescent CDs were introduced in detail.Chapter two: The water soluble nitrogen-doped CDs(N-CDs)with blue emission were obtained by using citric acid and diethylenetriamine through microwave method within 2 min.The strongest fluorescence emission band,located at 450 nm,was observed under the optimal excitation wavelength of 360 nm and the relative fluorescent quantum yield was 27.7%.The N-CDs showed excellent optical stability.The fluorescence intensity of the N-CDs could besignificantly quenched by mercury ion(Hg2+)and upon addition of glutathione(GSH)could recover the fluorescence intensity of the N-CDs-Hg2+ system obviously.An “on-off-on” mode was developed for the detection of Hg2+ and GSH with high sensitivity and selectivity based on the N-CDs fluorescent probe.The limit of detection of Hg2+ and GSH were 23 nM and 59 nM,respectively.Furthermore,the N-CDs-based probe was successfully applied to the determination of Hg2+ in water samples and employed as visualizing the intracellular Hg2+ and GSH sensors in live HeLa cell due to excellent reversibility.Chapter three: The water-soluble fluorescent CDs with excitation dependency were obtained by one-step hydrothermal method using Lycii Fructus as raw material,in this chapter.The CDs had no further surface modification.The relative quantum yield of the CDs was 17.2%,it was higher than other CDs prepared from natural products.Moreover,the CDs emitted a broad fluorescence between 415-545 nm and their fluorescence was tuned by changing excitation wavelengths.Moreover,the CDs exhibited excellent sensitivity and selectivity toward Fe3+ with a detection limit of 21 nM.The CDs were successfully applied to the determination of Fe3+ in samples and living cells.Meanwhile,the CDs possessed excitation wavelength dependence and many excellent features such as stable fluorescent properties,and were employed as fluorescent probes for multicolor imaging of He La cells successfully.Chapter four: In this chapter,diethylenetriaminepentaacetic acid(DTPA)reacted with o-phenylenediamine(o-PDA),m-phenylenediamine(m-PDA)and p-phenylenediamine(p-PDA)respectively through hydrothermal method,and three kinds of water-soluble CDs(o-CDs,m-CDs and p-CDs)were synthesized.The results showed that the fluorescent colors of the obtained CDs were directly related to the structure of phenylenediamine,and the fluorescent colors of the CDs of o-PDA,m-PDA and p-PDA were blue,green and red in turn.The optimal excitation wavelengths of o-CDs,m-CDs and p-CDs were 360 nm,445 nm and 570 nm,and the optimal emission wavelengths were 430 nm,510 nm and 600 nm,respectively.The three CDs had been used for multi-color cell imaging of HeLa cells successfully,and m-CDs could stain the cell nucleus.The fluorescent intensity of these three CDs were affected by pH,and these CDs were likely to be used as a p H sensor for monitoring intracellular p H levels.In this work,the fluorescent CDs with different emission colors were successfully prepared by using simple materials,which provided a new idea for the regulation of fluorescent color of CDs.