Prparation Of Carbon Quantum Dots And Its Application For Detection In Food

The research progress and current status of fluorescence detection and tradional methods in food inspection were briefly illustrated.The advantages and disadvantages of CQDs based on their applications in this field were discussed.The excellent properties and the current status of CQDs in the application field were summarized.The methods of preparing CQDs were summarized.CQDs was one step synthesized.The preliminary detections conditions of the CQDs were surveyed and the scheme of the thesis was basically determined.Details covered:(1)Water-soluble carbon quantum dots(CQDs)were prepared by using citric acid as carbon source.The obtained CQDs showed a strong emission at the wavelength of 484 nm,with an optimum excitation of 394 nm.Sunset yellow with maximum absorption wavelength at 482 nm could selectively quench the fluorescence of CQDs.Based on this principle,a fluorescent probe was developed for snset yellow determination.Furthermore,the quenching mechanism of the CQDs was elucidated.A linear relationship was found in the range of 0.1-100 ?mol/L sunset yellow with the detection limit(3?/k)of 0.051 ?mol/L.Satisfactory results were achieved when the method was submitted to the determination of sunset yellow in liquid samples.(2)We report that a rapid method of fluorescence turn-on assay for detection of melamine using carbon quantum dots(CQDs).The initial strong blue fluorescence of the CQDs was greatly quenched by Hg2+.The quenching mechanism may involve transfer of electrons from negatively charged group in the surface to Hg2+ cations by means of electrostatic interaction.The quenched fluorescence can be greatly recovered by adding melamine,because melamine could coordinate with Hg2+ through amino-group to form stronger metal-azyl bond,which take away Hg2+ from the surface of CQDs.Under the selected conditions,the response was linearly proportional to the concentration of melamine within the range of 3.0-60 mg/L,the limit of detection was 2.2 mg/L.(3)Carbon quantum dots(CQDs)with quantum yield of 11%were successfully synthesized via a simple,low-cost,and green hydrothermal treatment using dried lemon peel as carbon source for the first time.The obtained CQDs showed a strong emission at the wavelength of 505 nm,with an optimum excitation of 425 nm.Carmine with maximum absorption wavelength at 508 nm could selectively quench the fluorescence of CQDs.Based on this principle,a fluorescence probe was developed for carmine determination.The quenching mechanism of the CQDs was elucidated.A linear relationship was found in the range of 0.20-30.00 mg/L carmine with the detection limit(3?/k)of 0.16 mg/L.Satisfactory results were achieved when the method was submitted to the determination of carmine in soft drinks.(4)Carbon quantum dots(CQDs)with quantum yield of 14%were successfully synthesized via a simple,low-cost,and green hydrothermal treatment using cigarette filters as carbon source for the first time.The obtained CQDs showed a strong emission at the wavelength of 465 nm,with an optimum excitation of 365 nm.Sudan I with maximum absorption wavelength at 477 nm could selectively quench the fluorescence of CQDs.Based on this principle,a fluorescence probe was developed for Sudan I determination.Furthermore,the quenching mechanism of the CQDs was elucidated.A linear relationship was found in the range of 2.40-104.0 ?mol/L Sudan I with the detection limit(3?/k)of 0.95 ?mol/L.Satisfactory results were achieved when the method was submitted to the determination of Sudan I in food samples.