Preparation Of Fluorescent Carbon Quantum Dots And Its Application In Drug Analysis And Cell Imaging

Carbon quantum dots（CQDs）,as one of the common fluorescent sensors,are widely used in biochemical analysis,fluorescence imaging and drug delivery due to their excellent fluorescence properties.In this paper,three CQDs were synthesized from different carbon sources in green,and the results were obtained by Transmission Electron Microscope（TEM）,X-ray Diffraction（XRD）,Fourier Transform Infrared Spectrometer（FT-IR）,X-ray Photoelectron Spectrometer（XPS）,UV-visible spectrophotometer（UV-vis）and fluorescence spectroscopy to characterize their structures and properties,and their applications as fluorescent sensors in the fields of drug analysis and cell imaging were explored.The specific research work is as follows:1.The carbon quantum dots with blue fluorescence,abbreviated as OP-CQDs,were synthesized using waste biomass orange peel as the carbon source,and were characterized to have a graphene-like structure of about 3.7 nm with abundant hydrophilic functional groups and good fluorescence properties,which can be well used for drug analysis and cell imaging.In this chapter,the OP-CQDs-FA-Fe³⁺/Ca²⁺"on-off"fluorescence sensors were constructed for the detection of drug FA and important metal ions Fe³⁺and Ca²⁺,respectively.The fluorescence intensity of OP-CQDs was found to be linear in the ranges of 5-90μmol/L and 0.3-2.5 mmol/L.The regression equations wereΔF=0.0045 C_FA+5.8505×10^-4（R₁²=0.9987,ΔF=F/F₀-1）andΔF=0.337-0.3481 C_FA（R₂²=0.9994,ΔF=F/F₀-1）,and the LOD of FA was calculated to be 0.153μmol/L.The method was successfully applied to the spiked assay of FA in folic acid tablets with the recoveries of 95.7%-104.5%.In addition,the fluorescence intensity was linear in the range of 5-80μmol/L with the concentrations of Fe³⁺and Ca²⁺,respectively,in the OP-CQDs-FA system in the presence of different concentrations of FA,and was successfully used for the spiked determination of Fe³⁺and Ca²⁺in human serum with the recoveries of 100.15%-100.48%and 98.05%-98.18%with high accuracy.The establishment of this"on-off"fluorescence sensor provides a new idea for the rapid and sensitive detection of drug FA and important metal ions Fe³⁺and Ca²⁺,respectively.Meanwhile,the survival rate and fluorescence imaging maps of Hep G2 cells under the analysis of high concentration of OP-CQDs showed that OP-CQDs have low cytotoxicity and good biocompatibility.2.Fluorescent carbon quantum dots with single excitation and double emission,referred to as BL-CQDs,were synthesized by extracting fresh Banyan leaves with a mixture of ethanol and acetone,and the resulting extracts were used as precursors.By characterization,the synthesized BL-CQDs were found to be about 1.7 nm,with graphene-like structures,containing a variety of hydrophilic functional groups on the surface,and with good fluorescence properties,and were discussed for ACE activity detection,ACEI inhibition activity evaluation and live cell Bel-7404 fluorescence imaging.The fluorescence intensity ratio of BL-CQDs(I₆₇₆/I₄₆₀)was found to be linear with ACE activity in the range of 0.02-0.8 U/L with a regression equation ofΔF=2.5371 C_ACE-0.0311 and LOD of 0.016 U/L.This method was successfully used in the detection of ACE activity in crude extracted porcine lung and human serum,providing a new method for the analysis of ACE activity in complex samples.The sensor also successfully investigated the inhibition efficiency of yellow anemone leaf flavonoid extract and captopril tablets on ACE activity,which was applied to the screening of ACEI.The low cytotoxicity and good biocompatibility of BL-CQDs were demonstrated by analyzing the survival rate and fluorescence imaging maps of Bel-7404 cells under high concentration of BL-CQDs.3.Nitrogen and phosphorus co-doped red fluorescent carbon quantum dots,abbreviated as NP-CQDs,with a particle size of about 0.7 nm,containing a variety of hydrophilic functional groups on the surface and with good fluorescence properties,were synthesized from o-phenylenediamine and phosphoric acid,which can be well used as hydrophilic carriers in drug delivery and cell imaging.The targeted release of antitumor drugs was achieved by linking biotin and the antitumor drug CPT to NP-CQDs by hydrogen bonding coupling.In the experiment,the drug loading efficiency of the NP-CQDs-biotin-CPT functional complex was measured to be 61.8%,and the cumulative drug release reached 91.39%when incubated for 60 h in a slightly acidic environment.Meanwhile,the cytotoxicity results of Bel-7402 showed that NP-CQDs and NP-CQDs-biotin had almost no toxic side effects on cells,while the prepared NP-CQDs-biotin-CPT functional complex had less than 50%tumor cell viability after 12h incubation,indicating that the functional complex can be used as a drug carrier for antitumor drug targeted delivery.