| Carbon dots(CDs)is a class of carbon nanomaterials with zero-dimension structure and favorable photoluminescence(PL)property.Since it was first reported in 2004,extensive research has been devoted to the synthesis,property modulation and application of CDs.Owing to its excellent solubility,stability,biocompatibility and low toxicity,CDs has shown promising potential in biological and medicinal field.So far,there are few study in the field of long-wavelength emission CDs,and the PL mechanism is still controversial due to the diverse synthesis routes and raw materials.Also,CDs in solid state often suffer from fluorescence quenching due to the π-πstacking of conjugated systems,like most small molecules or organics.Such issues will greatly limit the development of CDs in various applications.Besides the exploration in basic properties of CDs,the biotical application of CDs is concentrated on bio imaging,drug delivery and cancer therapy.With the increasing attention of society to health issues,it is indispensable to further explore the biologic safety of CDs.In this thesis,we synthesized the CDs that can be used as bioimaging agent and fluorescent ink.And it can generate bright yellow PL in solid state without any additional matrix,meanwhile it owns concentration-dependent PL emission in solution.Subsequently,we made further analysis on this phenomenon,hoping it could bring some significant meaning to the future synthesis and regulation of carbon nanomaterials.Besides,we investigated the interaction of CDs with two serum proteins,human serum albumin(HSA)and γ-globulins,which may offer promising inspiration to the biosafety of nanomaterials.The thesis consists of five chapters:Chapter 1: This chapter introduces a comprehensive overview of synthetic routes,fluorescent properties,application and biological effect,also illustrating the significance and innovation of this topic.Chapter 2: Hydrothermal synthesis was used to obtain the blue-emitting CDs with high crystallization and uniform distribution.We analyzed the compositional elements,main functional groups,PL property and chemical durability of CDs.Also finding that CDs in solid state can emit yellow PL.Using the excellent biocompatibility and PL property of CDs,it has been successfully applied to biological imaging and fluorescent inks.Chapter 3: In this chapter,the concentration-dependent PL property of CDs was further analyzed and discussed.When CDs monomers were dissolved in aqueous solution,the self-assembly behavior appeared with the concentration rising,meanwhile the PL emission shift from blue to green region.While the solid CDs emits yellow PL and the solid monomers are inclined to assembly into spherical structure.Combining the results of Zeta potential and fluorescent lifetime,we developed a model for PL conversion and monomers assembly of CDs as the concentration varies:When the CDs monomers are dispersed in solution,it emits blue PL;when the concentration increases,the CDs monomers are assembled into aggregates due to the intermolecular force,meanwhile the PL emission shift to long-wavelength region;while in solid state,the π-π conjugated domain is enlarged,resulting in the bathochromic yellow emission.In view of the above analysis,we proposed a mechanism for the redshift of CDs PL caused by surface state electron rearrangement,which may provide referential significance for the synthesis and performance regulation of nanomaterials.Chapter 4: This chapter investigated the interaction between CDs with HSA andγ-globulins to explore its biosafety in biotical applications.It turns out the quenching effects of CDs on the two proteins are both dynamic quenching.Ultraviolet-visible(UV-vis)differential spectrometry and transient state fluorescence spectrometry were also utilized to further confirm their quenching types.The interaction forces are hydrogen bond,van der Waals forces and electrostatic forces for HSA and γ-globulins,respectively.By fitting the van’t Hoff equation,the thermodynamic parameters of relevant reactions such as enthalpy change,entropy change and Gibbs free energy are also obtained.Furthermore,the effect of CDs on the conformational structure of proteins was characterized by synchronous fluorescence spectra(SFS),three-dimensional(3D)fluorescence and circular dichroism(CD)spectra.This research could provide valuable information for the reliable application of nanomaterials at the biological level and medical theranostic field.Chapter 5: Summary and outlook.This chapter first summarized the overall structure of the paper,from the synthesis of CDs to the exploration of properties,and then to the biological effects.Subsequently the development potential and significance of CDs in structural characterization,luminescence regulation and application technology are discussed. |
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