Construction And Application Of Ratiometric Fluorescence Probe Based On Biomass Carbon Quantum Dots

Carbon Quantum Dots?CQDs?are a new type of carbon nano-functional material,which have stable optical properties and easy to achieve surface functionalization,as well as good biocompatibility and low cytotoxicity.Currently,most of the CQDs synthesis are mainly based on synthetic carbon compounds,with complex preparation process and harsh reaction conditions.Recently,due to the concept of green life and green chemistry,more and more scientists start to looking for more economic,green and environmental protection raw materials to synthesize CQDs.Natural biological materials,due to the low cost,easy to obtain and pollution-free,and also contain high quality of carbohydrates and protein,can be used as good carbon source to synthesize CQDs.Therefore,the synthesis of CQDs through these natural biological materials have been increasily reported,where melon seeds,nectarine,jujube and other natural biomass organic carbon sources were used to synthesis CQDs with excellent fluorescence properties.The raw materials were green and nontoxic,which make the synthesized CQDs is nontoxic as well.Thus,they have been widely used in biological imaging,biomarker,environmental detection,photocatalysis and drug detection and analysis and so on.There are fluorescence analysis method based on CQDs have been reported,while most of them were detected with single wavelength fluorescence intensity signal.These can be easily affected by the fluctuation of light source intensity and external environment such as temperature and humidity and so on,which would highly disturbed the accuracy of experimental results.Ratiometric fluorescence probes usually collect signals of two or more characteristic emission wavelengths,and determined the target analyte according to the ratio change of those two emission peaks.Compared with the signal wavelength measured fluorescence signal,ratiomeric fluorescence probe show stronger anti-interference ability and clearly improved the detection accuracy.The study of ratiometric fluorescence probe based on CQDs has now become a hotspot.In this thesis,the synthesis of CQDs with biological materials and the construction of ratiometric fluorescence probes with these CQDs as a response signal or reference signal respectively were studied,which can not only provided a new method for fluorescence detection of target analytes,but also expanded the application scope of the CQDs in analysis detection.The main work of this thesis is as follows:1 Green fluorescent castor carbon quantum dots?CO-CQDs?with excellent fluorescence properties were synthesized by one-step hydrothermal method with natural biomass peeled castor.Combining the as-synthesized CO-CQDs with Eosin Y?EY?,a novel ratiometric fluorescence probe CO-CQDs/EY was formed.In the Na2HPO4-citric acid buffer solution of pH=4.00,under the excitation wavelength of 320 nm,the CO-CQDs/EY complex showed two independent fluorescence emission peaks at 405 nm and 540 nm,respectively.The fluorescence signals of 405 nm and 540 nm could be simultaneously quenched by Cr?VI?.While,in the present of L-ascorbic acid,the fluorescence signal at 540 nm was significantly strengthened,while the fluorescence intensity at 405 nm still remained unchanged.Therefore,a novel method for L-ascorbic acid analysis was developed based on this fluorescence ratiometric probe CO-CQDs/EY.This ratiometric method showed excellent specificity,sensitivity and accuracy.The optimum conditions of experiment were investigated and the mechanism of interaction was discussed.Under the optimized experimental conditions,the linear range of this method was 0.05-4.0?M,and the detection limit was calculated to be 0.037?M.Moreover,this method has been successfully applied to L-ascorbic acid analysis in drugs,vegetables and fruits,showing great potential in real sample analysis.2 Natural biomass“hyacinth bean”was chose as carbon source,after mixing with pure water,a green,soluable and non-toxic“hyacinth bean”CQDs?HB-CQDs?with excellent fluorescence property were synthesized by one-step hydrothermal method.Meanwhile,a new complex with high resolutionable fluorescence emission peaks were formed by mixed HB-CQDs with isothiocyanate fluorescence?FITC?.It was found that the HB-CQDs/FITC complex shows double fluorescence emission peaks in 400 nm and510 nm,and both peak were able to be quenched by MnO₄^-through radiation energy transfer,which makes the fluorescence intensity of the complex significantly decreased and“close”the fluorescence signal.The fluorescence signal was“re-open”,after adding lonoxicam?LNXC?to the system,which is due to the radiation energy transfer process was hindered by the combination of LNXC and MnO₄^-and restored the flluorescence intensity in 510 nm,while the signal at 400 nm was remained.The optimum conditions to recover the fluorescence signal and the affectable factors were detected,the mechanism of interaction between MnO₄^-and HB-CQDs/FITC and the fluorescence quenching types were discussed.After measuring the fluorescence lifetime and ultraviolet-visible absorption spectra,the fluorescence quenching type was defined as dynamic quenching.Under the optimum experimental conditions,the determination of LNXC was achieved according to the good linear relationship between the fluorescence intensity ratio?I510/400?of the complex and the concentration of LNXC in the range of 0.1-10?M,the detection of LNXC was successfully achieved.3 Dandelion and ethylenediamine were selected as carbon and nitrogen sources,respectively,nitrogen-doped dandelion carbon quantum dot?DE-CQDs?was first synthesized,following with absorbtion of rhodamine 6G?Rh6G?on the surface DE-CQDs by electrostatic interaction,thus,a ratiometric fluorescent probe based on DE-CQDs to detect Hg²⁺and L-phenylalanine?L-Phe?was designed.Under the sigle excitation wavelength of 343 nm,this probe showed double emission peaks of 425 nm and 550 nm in BR buffer?pH=4.00?.Since the fluorescence signal of 425 nm was quenched after adding Hg²⁺in the buffer,while fluorescence signal of 550 nm was unaffected,a method use DE-CQDs as the response signal and Rh6G as the reference signal for measuring Hg²⁺was established,and the quenching ratio of the fluorescence intensity I_425/550 at the two emission peaks showed a good linear relationship with Hg²⁺at the concentration in the range of 1.0-20?M;and the fluorescence signal of 425 nm was restored with the addition of L-Phe.Under the optimum experimental conditions,since the fluorescence intensity recoveried ratio of DE-CQDs/Rh6G complex probe of 425 nm and 550 nm had a good linear relationship with the concentration of L-Phe ranging from0.50-10?M,a new method has been established with the detection limits of 0.20?M of Hg²⁺and 0.24?M of L-Phe,respectively.This probe was applied to the detection of L-Phe with satisfactory results in food sweeteners-aspartame.