Preparation And Modification Of Biomass Based Carbon Quantum Dots And Their Application In The Detection Of Copper Ions

Copper ions(Cu²⁺)which is the third most abundant transition metal ion in the human body play a crucial role in biological systems.As the cofactor of many enzymes,the content of copper ion will have a huge impact on biological systems.At present,there are many methods for the detection of Cu²⁺,and the fluorescence detection technology has attracted much attention because of its high sensitivity,easy operation,less spectral interference and wide absorption band.However,most of the fluorescent probes use organic solvents mostly and the poor solubility in water,it will limit the probe in the environment and its biological applications.Carbon Quantum Dots?CQDs?,a novel fluorescent material discovered in 2004,are characterized by outstanding fluorescence,good optical stability and easy surface modification,especially their excellent biocompatibility and low toxicity.It is considered to be a powerful alternative to metalsemiconductor fluorescent dye material.However,compared to inorganic quantum dots and organic dyes,the fluorescence quantum yield of carbon dots is lower.Therefore,it is of great significance to prepare a carbon quantum dot with high fluorescence quantum yield,good fluorescence property and biocompatibility.Based on the above,the main contents of this paper are as follows:1)By using the mangosteen shells as the raw material,the carbonized mangosteen shells with carbon content of more than 75% and relatively complete carbon network structure was obtained by one-step carbonization method.The perfection of structure of mangosteen shells is helpful for the preparation efficiency of CQDs.2)The water-soluble CQDs with blue green fluorescence were prepared by carbonic acid-catalyzed oxidative cleavage from carbonized mangosteen shells.The average size of the carbon quantum dots was 2.7 nm,and the lattice spacing was 0.246 nm,corresponding to the?001?plane of graphite.FTIR spectra analysis showed that the surface of CQDs is rich in hydroxyl and carboxyl groups,which means the good water solubility and easy to modification.3)The CQDs were modified by one-step hydrothermal method on the basis of the mangosteen shells based quantum dots,and the surface of the CQDs was enriched with amino groups whichcould react with Cu²⁺.FTIR spectra analysis showed that BPEI was successfully modified on the CQDs' surface.After optimization,the fluorescence intensity of BPEI-CQDs could be greatly enhanced,and the fluorescence quantum yield was improved from 3.7% to 21.6%. Besides,the fluorescence emission peak moved to blue shift,which could emit bright blue light under the ultraviolet light.Through the fluorescence response for BPEI-CQDs to different ions and Cu²⁺ ions with different concertation,the fluorescence of BPEI-CQDs was quenched,so that BPEI-CQDs can show specific recognition to Cu²⁺.The degree of fluorescence quenching linear range of BPEI-CQDs is 5⁶0 ?mol/L and the detection limit can reach to 0.69 ?mol / L, which can meet the requirements of the detection of Cu²⁺ in the human body?10-4 10-6 mol / L?.4)The as prepared BPEI-CQDs were applied to the imaging of mouse fibroblast L929 cells and intracellular copper ion detection.MTT test results showed that BPEI-CQDs exhibited low toxicity and good cell membrane permeability.BPEI-CQDs could pass through the cell membrane and stay in the cytoplasm.The colour of fluorescence imaging in L929 cells was changed when the excitation wavelength changed,which corresponding to that the emission wavelength of the BPEI-CQDs depends on the excitation wavelength.Under the action of exogenous Cu²⁺,the intracellular fluorescence was quenched,which provided suggestion for the detection of intracellular Cu²⁺.