Investigations On The Regulation Of The Physical And Chemical Properties Of Carbon Nanodots And Bioimaging Applications

Carbon nanodots(CNDs)are newly emerged fluorescent nanomaterials with unique features like feasible preparation and functionalization,controllable optical properties,low cytotoxicity,and hardly attacked by the immune system.They have shown great potentials in catalysis,chemical sensing,and bioimaging.Exploring new approaches to prepare functionalized CNDs and regulate their physical/chemical properties is vital for elucidating the fluorescent mechanisms and improving the investigations in bioimaging.A series of studies have been conducted on regulating the physical and chemical properties of CNDs,e.g.,biocompatibility,fluorescent features and hydrophilicity/hydrophobicity,as well as their applications in bioimaging analysis.The applications of bioimaging technology in practical studies and medical diagnosis are introduced in Chapter 1,by reviewing the various species of CNDs.The fluorescent features and fluorescent mechanisms of CNDs are also introduced,as well as the applications of CNDs in sensing,fluorescent bioimaging and biomedicine are also depicted.In addition,the application of ionic liquids in preparation of CNDs is introduced.The improvement in biocompatibility of CNDs via surface modification is illustrated in Chapter 2.In the practice of in vivo imaging with CNDs as probe,the volume of CNDs solution introduced into living body should be kept at minimum,and a higher concentration is needed to ensure high fluorescent analysis quality.Therefore,the improvement on biocompatibility of the CNDs is among the most critical issues.Amide group functionalization of CNDs is first conducted through microwave irradiation with glucosamine as carbon source and PEI and DTM as passivation agents,followed by coupling the ionic liquid 1-carboxymethyl-3-methyl imidazolium bromide on the surface of the Amide-CNDs via covalent conjunction to produce the ionic liquid modified CNDs(IL-CNDs).MTT test results indicate that cell viability decreases to ca.80%when incubated with Amide-CNDs at concentration of 1.0 mg mL-1.While the cell viability still remains ca.75%when incubated with IL-CNDs at 10 mg mL-1.These observations clearly show a much improved biocompatibility by the modification of CNDs with ionic liquid moiety.In addition,the as-prepared CNDs show potentials in multi-color bioimaging,which is demonstrated by successful HeLa cell labeling with blue(420 nm)and green(520 nm)fluorescence emission.In Chapter 3,fluorescence-tunable carbon nanodots are prepared via hydrothermal treatment of 1-ethyl-3-methylimidazolium bromide.The characterization results of infrared spectroscopy and X-ray photoelectron spectroscopy indicate the presence of short alky chain and aromatic structures.The aromatic structures aggregate into conjugated electron domain with increase of concentration,endowing CNDs concentration dependent fluorescent emission.The maximum excitation/emission wavelengths shift from 360/450 nm to 480/540 nm with the concentration increases from 0.12 mg mL-1 to 8.0 mg mL"1.The obvious fluorescence emission in infrared region indicates the potentials in bioimaging.On the other hand,the surface states of CNDs endow them hydrophobicity,facilitating the interaction between CNDs and cell membrane.The as-prepared hydrophobic CNDs penetrate cell membrane via multiple pathways,e.g.,caveolin-and clathrin-dependent endocytosis and passive diffusion,making the penetration process feasible within 1 min.This rapid penetration behavior significantly reduces the sample treatment time,which is preferential for avoiding possible fluorescence quenching induced by interaction between CNDs and samples.Co-location study with commercial dye reveals that the hydrophobic CNDs distribute mainly in lysosome,which makes it a potential probe for lysosome.The cell labeling investigations for three cell lines,e.g.,HeLa cells,MCF-7 cells and A549 cells,indicate that the CNDs are broad-spectrum fluorescence probe for various carcinoma cells.Moreover,obvious fluorescence signal can be observed in the position of liver after intravenous injection of CNDs into live mice,demonstrating the potential of CNDs as fluorescence probe for in vivo imaging analysis.The regulation of hydrophilicity/hydrophobicity of CNDs at will is most important.Therefore,in Chapter 4,the regulation of hydrophilicity/hydrophobicity of CNDs is achieved via one-pot hydrothermal treatment method with hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate as the carbon source in a H3PO4-ethanol medium.Hydrophilic and hydrophobic CNDs are obtained simultaneously with H3PO4/ethanol molar ratio within 0-1.72,while hydrophilic or hydrophobic CNDs are the sole product obtained from H3PO4-BmimPF6 or BmimPF6-only systems.The proportions of hydrophilic and hydrophobic CNDs are simply regulated by varying the H3PO4/ethanol molar ratio.The surface state analysis results indicate that hydrophilic CNDs and hydrophobic CNDs are covered with carboxyl/hydroxyl groups and hexafluorophosphate groups,respectively,which endow them hydrophilicity or hydrophobicity.Both the hydrophilic and hydrophobic CNDs exhibit excitation-dependent fluorescence feature with maximum fluorescence at 360/440 nm(hydrophilic)and 430/510 nm(hydrophobic),respectively.The cell labeling investigations for HeLa cells indicate the blue and green fluorescent emission when incubated with hydrophilic CNDs and red fluorescent emission when incubated with hydrophobic CNDs.In summary,both hydrophilic and hydrophobic CNDs obtained by this approach exhibit favorable biocompatibility and offer favorable performance in bioimaging as demonstrated for the fluorescent labeling and imaging of live HeLa cells.