Synthesis And Bioimaging Performance Of Chiral Carbon Quantum Dots Based On Stereo Structure Inheritance Strategy

Chiral carbon quantum dots（CQDs）,as a new functional carbon nanomaterial,possess chiralityas well as tunable emission wavelength,superior photostability,low toxicity,and good biocompatibility.Chirality plays an important role in biology,chemistry,and medicine,which will broaden the application of CQDs in targeting imaging,chiral catalysis,chiral recognition,and chiral detection.In view of the immature preparation,short emission wavelength,and unclear chirality mechanism of chiral CQDs,the strategy of stereo structure inheritance was adopted to synthesize chiral CQDs with different structures and optical activities via one-step hydro-/solvothermal method from different chiral sources.Their morphology,structure,optical properties,fluorescence,and chirality mechanism were investigated,and the effects of their optical activity on targeting imaging performance of Golgi apparatus were investigated.The main work is divided into the following four parts:（1）Synthesis of enantiomeric carbon quantum dots and their cell imaging performance.To obtain enantiomer CQDs,blue emissive L-and D-CQDs were synthesized by one-step hydrothermal method from L/D-Tryptophan（L/D-Trp）,a widely available and low-cost amino acid in nature,as the chiral and carbon source.They have similar morphology,structure and optical properties,and show opposite and symmetrical circular dichroism signals,indicating that they are enantiomers.The magnitude of the asymmetric g-factor is 10^-5.Control experiments show that the circular dichroism signal of L/D-CQDs not only inherits the chirality of L/D-Trp on the surface of CQDs,but also generates two new chiral signals induced by chiral environment.Finally,L-and D-CQDs with low toxicity were applied to cell imaging,as they can enter cells for cytoplasmic imaging.（2）Synthesis of chiral carbon quantum dots with high optical activity and their Golgi targeting imaging performance.In order to improve the optical activity of chiral CQDs,the L-CQDs with blue emission were synthesized facily by one-step hydrothermal method from L-Ascorbic acid（L-AA）with high reactivity,as chiral and carbon source,and ethylenediamine as nitrogen dopant.The fluorescence of L-CQDs originated from the carbon core and surface state,and the latter is dominant.The chirality of L-CQDs is completely inherited from L-AA and located on the surface of CQDs.L-CQDs possessed satisfactory photostability,good biocompatibility,and low toxicity,applicable to Golgi targeting imaging.（3）Synthesis of blue emissive chiral carbon quantum dots with cysteine residues and their Golgi targeting imaging performance.In order to improve Golgi targeting imaging ability of L-CQDs,cysteine（Cys）residues were introduced into L-CQDs.Blue emissive L-CQDs with Cys residues were synthesized by one-step hydrothermal method with L-AA as chiral and carbon source,and L-Cys as the Golgi targeting unit.Their fluorescence were derived from carbon core and surface state;The circular dichromatic spectra showed that L-CQDs are chiral and the g-factor is on the order of 10^-4.In addition,L-CQDs exhibited excitation dependence,satisfactory photostability,good biocompatibility and low toxicity,and can be used as a Golgi targeting imaging agent for Golgi targeting imaging,Their Pearson correlation coefficient is 0.62.（4）Synthesis of orange emissive chiral carbon quantum dots with cysteine residues and their Golgi target-imaging properties.In order to increase the content of Cys residues in chiral CQDs,further improve their Golgi targeting imaging ability,and broaden their emission wavelength to avoid autofluorescence interference,the long wavelength chiral CQDs with Golgi targeting ability were achieved.By adopting structure inheritance strategy,L-and D-CQDs with excitation-dependent orange emission were synthesized by one-step solvothermal method from L/D-Cys as chiral source and Golgi targeting unit,and neutral red as carbon source.The fluorescence originated from carbon core and surface states.L-and D-CQDs have obvious circular dichromatic signal,the order of asymmetrical g-factor is 10^-4.In addition,their have good fluorescence and chiral stability,low toxicity,and good biocompatibility.When applied L-and D-CQDs to Golgi targeting imaging,their Pearson correlation coefficients are 0.99 and0.97,respectively.At the same time,chiral CQDs emit orange light,which can penetrate biological tissues for in vivo imaging.The morphology,structure,optical properties and Golgi targeting performance of a series of chiral CQDs were invesgated.It was found that the high optical activity of CQDs and the presence of Cys residue could synergically improve the Golgi targeting imaging performance.Therefore,as a good Golgi targeting imaging agent,chiral CQDs should be rich in Cys residue and high optical activity,and the emergence of chiral CQDs also provides a low-cost imaging agent for Golgi targeting imaging.