The Synthesis Of Carbon Quantum Dots Derived From Pomegranate Seeds And Their Application

Fluorescent carbon quantum dots(CQDs)have drawn tons of attention due to their superior properties such as low cytotoxicity,resistance to photobleaching,emission tunability,good biocompatibility and high photostability,since they were first discovered in 2004.Up to now,various synthetic methods and different carbon sources have been reported for the preparation of CQDs,and CQDs have been successfully applied for bioimaging,biosensing,photocatalysis,optoelectronic device and so on.However,synthesizing surface-functioned CQDs with highly luminescent properties as effective fluorescent probes for biological and environment detection is still a challenge for researchers.In this thesis,four CQDs with different luminescent properties are prepared by using pomegranate seeds as carbon source and ethylenediamine,amino acid,riboflavin as surface passivation agents,respectively.And the as-prepared CQDs are employed as fluorescent probes for highly sensitive detection of dopamine,glutathione,parathion and Hg2+,respectively.The main research contents are as follows:CQDs are synthesized by using a facile one-step microwave assisted pyrolysis with pomegranate seeds as carbon precursor and ethylenediamine as surface passivation agent.The CQDs show bright blue photoluminescence under ultraviolet light.Besides,CQDs can respond to the acid-alkali of solutions sensitively.Moreover,the fluorescence of CQDs can be quenched by dopamine due to their electrostatic interaction.Based on that,a new strategy for highly sensitive and selective determination of dopamine is established by using the as-prepared CQDs as fluorescent probes.The linear detection range for dopamine is from 0.1 to 8 ?g/mL with the detection limit of 31 ng/mL.The proposed method has been applied for the detection of dopamine in human serum and urine samples with RSD less than 3.1%,and the recovery values are within 98.0-103.5%.Furthermore,the as-prepared CQDs can be used for bioimaging in zebrafish,suggesting good biocompatibility of CQDs.Fluorescent CQDs are prepared by hydrothermal treatment using pomegranate seeds as carbon source and ethylenediamine as surface passivation agent.The as-prepared CQDs display blue photoluminescence with a high quantum yield(23.80 %).Besides,the fluorescence of CQDs can be quenched by Hg2+ due to the combination of Hg2+ with-COOH and-OH on the surface of CQDs,resulting in the electron transfers from excited state of CQDs to empty “d” orbit of Hg(II).While glutathione can bond to Hg2+ selectively via the formation of Hg-S bond,resulting that Hg2+-CQDs complex dissociates,which leads to the the fluorescence recover of CQDs.Furthermore,an “off-on” fluorescent method is proposed for highly sensitive detection of glutathione.The enhanced fluorescence intensity is well proportional to the concentration of GSH in the range from 0.1 to 6 ?M with a low detection limit of 32 nM.The proposed method can be used for the determination of glutathione in biological samples.Pomegranate seeds,DL-tryptophan and DL-aspartic acid are employed as the raw materials to synthesize CQDs by hydrothermal treatment.The as-prepared CQDs show blue photoluminescence with a high quantum yield of 35.78 %.The surface defects of CQDs may be reduced because of the interaction between parathion and CQDs,which is not beneficial for the nonradiative recombination between excited electrons in the conduction band(e-)and electron hole in the valance band(h+),resulting in the fluorescent enhancement of CQDs.Thus a new fluorescence enhanced strategy for the detection of parathion is established with a linear range from 0.01 to 1.1 ?M,and a low detection limit of 3.7 nM is obtained.The proposed method has been applied to detect parathion in environmental samples with RSD less than 3.2%.The recoveries are from 98.0 to 102.7 %.Nitrogen doped CQDs(N-CQDs)are prepared from pomegranate seeds in the presence of riboflavin by hydrothermal treatment.The as-prepared N-CQDs display yellow-green photoluminescence with high quantum yield to be 38.83 %.Moreover,N-CQDs-based fluorescent probes for highly sensitive detection of Hg2+ is developed based on effective fluorescence quenching of N-CQDs.Based on that,a linear relationship is obtained in the range of 0.05-7 ?M with a detection limit of 29 nM Hg2+.The proposed method can be used for the determination of Hg2+ in river water,lake water and tap water.The study on fluorescence quenching mechanism indicates that both static and dynamic quenching processes occur in the system.