Preparation And Bioimaging Properties Of Fluorescent Carbon Dots From Cellulose Hydrogel

The fluorescent probe is essential in biomedical research,and the quantum dots fluorescent probe attracts interest with the development of nanotechnology.The presently used quantum dots in biological imaging are semiconductor quantum dots,however,the biocompatibility of these semiconductor quantum dots is not satisfied.Therefore,carbon quantum dots?CDs?is expected to be used for in vivo labeling due to its excellent biocompatibility.To prepare the CDs,biomass materials were considered as carbon sources because they are environmental-friendly materials.Cellulose,the most representative biomass,has been used to prepare CDs in the form of powder or short fibers.To prepare the element-doped CDs,such problems as poor doping efficient and low utilization of raw material need to be considered.In this work,cellulose hydrogel was used as the carbon source and doping-material-carrier to produce CDs and element-doped CDs.The influence of the chemicals that carried in the cellulose hydrogel on the generated yield?GY?,the chemical structure,and the optical properties of the so-produced CDs were studied.The effect of the size of CDs on their optical properties was also studied.The in vitro cytotoxicity and in vivo safety of CDs were studied,and the influence of the chemicals that carried in the cellulose hydrogel,the particle size of the CDs,and the cell type on the bioimaging quality of living cells performance of CDs were investigated,and the application possibility of so-produced CDs for in vivo biological imaging was discussed.The experimental results obtained in this study may provide a reference to the preparation and biological application of biomass-based CDs.In this work,several kinds of element-doped CDs with luminescent properties were prepared by the one-step hydrothermal method using cellulose hydrogel as both the carbon source and the doping-material-carrier,and the generated yield?GY?of CDs was detected.Subsequently,the morphology and microstructure of CDs were observed by means of High-resolution transmission electron microscope?HRTEM?,and the chemical structure and groups of CDs were analyzed by means of Ultraviolet-visible spectrophotometer?UV-Vis?,Fourier infrared spectroscopy?FTIR?and X-ray photoelectron spectroscopy?XPS?.The optical properties of so-produced CDs were studied by means of fluorescence spectrophotometer?PL?and the quantum yield?QY?of the CDs was calculated.The LDH assay and CCK-8 assay on Human Amniotic Epithelial Cells?AECs?were proformanced to investigate the cytotoxicity of the CDs,and the in vivo biocompatibility was evaluated by histopathologic observation and Bcl-2/Bax Elisa assay of the heart,liver,lung,spleen and kidney of the SPF sprague-dawley?SD?rats that intravenous injected with CDs solution through the tail vein.The influence of chemicals carried in cellulose hydrogel,as well as the particle size of the CDs on the bioimaging quality of AECs and Hela cells were studied via individually labeling or co-marked with ER-Tracker Red and Phalloidin TRITC.Besides,the in vivo biological imaging property of CDs was studied by the frozen section observation and fluorescence measurement of the tissues in SD rats.The experimental results show that:1.The CDs that doped with N or S were successfully obtained by using cellulose hydrogel that carried with different chemicals such as NaOH,urea,thiourea and?NH₄?₂SO₄ as the carbon source,and the GY of CDs that produced by chemical-carried cellulose hydrogel are much higher than that produced by pure cellulose hydrogel.2.CDs prepared from cellulose hydrogels that carried with different chemicals exhibit similar fluorescence spectral properties.The maximum QY of the CDs obtained in this experiment reaches to 0.227�0.002,and decreases in the following sequence:?NH₄?₂SO₄/cellulose hydrogel CDs>NaOH/urea/cellulose hydrogel CDs>urea/cellulose hydrogel CDs>NaOH/cellulose hydrogel CDs>cellulose hydrogel CDs>Thiourea/cellulose hydrogel CDs.For the same kind of CDs,the smaller the particle size of the CDs is,the higher the QY is.3.CDs prepared from cellulose hydrogel have almost no cytotoxicity and tissue toxicity in rats and can be used for bioimaging of in vitro living cells and in vivo.4.CDs were unevenly distributed in the cytoplasm of living cells,and cell morphology can be effectively fluorescently labeled,and it has no selective labeling function for endoplasmic reticulum and F-actin.The brightness of the labeled image was determined by both the QY of CDs and the CDs-uptaken of the living cells.For the same kind of cells,there is a positive correlation between the labeled brightness and the QY of the CDs;for the same kind of CDs,the labeled brightness of Hela cells is higher than that of AECs.5.CDs injected into rats only remained in the liver,kidney and spleen after 1 h of injection and showed blue fluorescent,and had no significant labeling effect on other tissues.