Preparation Of The Fluorescence Probes Based On Novel Carbon-based Quantum Dots And Their Application In Biosensing And Bioimaging

As a new class of attractive fluorescence nanomaterials,carbon based quantum dots particles smaller than 10 nm,have attracted wide attentions of scientists in diverse research fields owning to their outstanding optical and chemistry properties.To compare with the traditional organic dyes and semiconductor quantum dots,carbon based quantum dots are more useful because of their large surface area,green synthesis,easy functionalization,excellent photostability,low cytotoxicity,favorable biocompatibility,and good water solubility.These outstanding physicochemical and optical properties promise their potential applications in fluorescence sensors,bioimaging,drug delivery,photocatalysis,and photovoltaic devices.Up to now,extensive efforts have been devoted to synthesizing carbon based quantum dots,however,most of these methods involve complex processes,produce low yield,and low fluorescence quantum yield.Thus,it is highly important to develop a simple,cost-effective and environmentally-friendly method for for the preparation of carbon based quantum dots.Herein,three novel fluorescent carbon based quantum dots were prepared by one step hydrothermal treatment or microwave-assisted strategies with biomass or cheap,low cost of chemical reagent as raw materials.Their applications in the fields of fluorescence sensors and bioimaging are presented.The main contents of this work can be concluded as follow:Part one:A facile hydrothermal synthesis strategy for fabrication of nitrogen-doped carbon quantum dots(N-CQDs)was developed using sugarcane bagasse as precursor.The morphology,structures and optical properties of the obtained N-CQDs were characterized by transmission electron microscope(TEM),Ultraviolet-Visible spectroscopy(UV-Vis),photoluminescence spectroscopy,Fourier transform infrared spectrophotometer(FT-IR)and X-ray photoelectron spectroscopy(XPS).The as-synthesized N-CQDs possess high water solubility,good photoluminescence stability,and excellent photostability.Additionally,the N-CQDs exhibit excitation-dependent emission with the maximum emission at 440 nm,and a high quantum yield of 9.5%is achieved at an excitation wavelength of 350 nm.Chlorotetracycline(CTC)can cause the fluorescence quenching effect of the N-CQDs more obvious,hereby,a simple and efficient method to measure the CTC was established.This sensing system exhibits a wide linear relationship with CTC concentrations from 0.04 ?mol/L to 30?mol/L and a detection limit as low as 0.01?mol/L.This sensing system exhibits excellent sensitivity and selectivity toward CTC,which was successfully applied in the detection of CTC in milk.Part two:A simple,facile,and economical hydrothermal strategy was developed for the synthesis of nitrogen-doped graphitic quantum dots(N-GQDs)using citric acid as carbon source and melamine as nitrogen source.The morphology,structures and optical properties of the obtained N-GQDs were characterized by TEM.UV-Vis,photoluminescence spectroscopy,FT-IR and XPS.The as-synthesized N-GQDs possess high water solubility,good photoluminescence stability,excellent photostability,and good tolerance for pH with a fluorescence quantum yield of 18%.Furthermore,on the basis of the effective quenching effect of metacycline(MTC),a new method was developed for the determination of MTC by using N-GQDs as fluorescent probe.This sensing system exhibits excellent sensitivity and selectivity toward MTC with a wide linear relationship from 0.1 ?mol/L to 120?mol/L and a low detection limit of 0.02?mol/L.It was successfully applied for the detection of MTC in mice plasma.Part three:A novel bright blue luminescent nitrogen and boron codoped carbon quantum dots(N,B-CQDs)was prepared via a facile and rapid microwave-assisted synthesis using citric acid,boric acid,and ethanol amine as the precursors.The as-prepared N,B-CQDs exhibited uniform spherical particles with an average of 2.5 nm.The strong emission with the maximum wavelength at 450 nm could be observed under excitation at 350 nm,and exhibit excitation-independent emission characteristic.The N,B-CQDs possess excellent water solubility,excellent stability under UV irradiation,strong resistance to the interference of high ionic strength environments,good tolerance for pH,and high fluorescence quantum yield(38.6%).The cell viability assay under a pretty high concentration of N,B-CQDs reveals low cytotoxicity and good biocompatibility.Based on these advantages,the N,B-CQDs can be used as a promising fluorescent probe for T24 cell imaging with great potential in bioanalysis and the related fields.