| Carbon Quantum Dots（CQDs）was a new kind of carbon nano-functional material.It had the excellent optical properties of high fluorescence intensity,good light stability,wide excitation spectrum,adjustable emission wavelength and large stokes shift.At the same time,CQDs had the advantages of environmentally friendly,non-toxic,simple synthesis and low cost,which has attracted much attention in the fields of analysis application,bioimaging,chemical sensing and gene transport.The early synthesis of CQDs mainly used artificial carbons compounds as raw materials.The preparation process was cumbersome and the reaction conditions were harsh.In recent years,some methods for preparing CQDs using natural materials such as aloe and strawberry have emerged.The selection of carbon source materials for the synthesis of CQDs and their luminescence properties characterization and analytical applications are becoming more and more active.CQDs were often used as fluorescent probes for the determination of inorganic ions in samples because of their excellent luminescent properties,but the application of CQDs as fluorescent probes for pharmaceutical preparation analysis was not very much.In this paper,a one-step hydrothermal method was developed for the preparation of CQDs with excellent properties by green natural materials.Using CQDs as the fluorescent probe,the quencher could turn off the fluorescence of CQDs,but the addition of some pharmaceuticals could restore the fluorescence signal.According to this principle,a"off-on"fluorescent probe was constructed for the highly sensitive detection of pharmaceuticals.This study not only provided a new method for fluorescence detection of pharmaceuticals,but also expanded the application of CQDs in the field of pharmaceutical preparation and analytical chemistry.The four processes are as follows:1.A one-step hydrothermal method was developed for the preparation of carbon quantum dots（CQDs）with strong fluorescence by using red dates as precursors.The luminescence properties of the red dates CQDs were studied by fluorescence spectroscopy,UV-Vis spectrum,transmission electron microscopy,infrared spectrum,X-ray powder diffraction spectroscopy.The fluorescence quantum yield was 5.1%.In pH=4.00 NaAc-HAc buffer solution,after KMnO4 was added in CQDs solution,the fluorescence of CQDs was quenched,and the fluorescence signal of the system was in the“off”state.In the presence of rutin,the fluorescence of CQDs was recovered because KMnO4 preferred to react with rutin,which results in the departure of KMnO4 from the surface of the CQDs,and the fluorescence signal of the system was“open”.The degree of recovery of CQDs fluorescence intensity was proportional to the rutin concentration,which provided a new method for the detection of rutin with high sensitivity and selectivity based on the fluorescence quenching-recovery properties of CQDs.The mechanism of fluorescence quenching of CQDs by KMnO4 was studied,and the reaction conditions were optimized.Under optimal conditions,the recovered fluorescence of CQDs was linearly related with the rutin concentration in the range 2.5×10-77 to 1.0×10-5mol/L,the detection limit was 1.5×10-77 mol/L.The present method was applied for the detection of rutin in samples with satisfactory results.2.Green non-polluting fluorescent carbon quantum dots were synthesized by one-step hydrothermal method using peanut as a carbon source.Based on its luminescent properties,a"off-on"fluorescent method was constructed for high sensitivity detection of dopamine（DA）by using the PN-CQDs as a probe.The experiments indicated that in pH=3.80 HAc-NaAc buffer solution,when Ce（Ⅳ）was added in PN-CQDs solution,the fluorescence of PN-CQDs was quenched,and the fluorescence signal of the system was in the“off”state.It was found that both electron transfer from PN-CQDs to Ce（Ⅳ）and aggregation of PN-CQDs were responsible for the PN-CQDs luminescence quenching.In the presence of DA,the fluorescence of PN-CQDs was recovered because Ce（Ⅳ）preferred to react with DA,which resulted in the departure of Ce（Ⅳ）from the surface of the PN-CQDs,the fluorescence signal of the system was“open”.The reaction conditions were optimized and under optimal conditions,the recovered fluorescence of PN-CQDs was linearly related with the DA concentration in the range 2.5×10-7-1.0×10-55 mol/L,the detection limit was 9.0×10-88 mol/L.The fluorescence quenching-recovery mechanism of the system was discussed.The fluorescence lifetimes of PN-CQDs and PN-CQDs-Ce（IV）systems were 6.02 ns and 5.15 ns,respectively.The fluorescence quenching type of PN-CQDs was dynamic quenching.The fluorescence of Ce（III）generated in the reaction atλex/λem=251 nm/350 nm had no effect on the determination of DA.The method was sensitive,simple and rapid.It has been applied to the determination of DA in practical samples.The recovery of standard addition was between 97.5%and 103.0%,and the results were satisfactory.3.CQDs with strong fluorescence was synthesized from black sesame by one-step hydrothermal method at 180℃for 24 h.The emission wavelength and intensity of the CQDs were strongly depended on the excitation wavelength.Based on Cu2+and CQDs could form a non-radiative complex,the"quench-recovery"fluorescent probe was constructed for high sensitivity detection of piroxicam.The experiments indicated that in pH=3.60 disodium hydrogen phosphate-citric acid buffer solution,the fluorescence of CQDs was quenched atλex=332 nm/λem=414 nm after Cu2+was added in CQDs solution,and the fluorescent signal of CQDs was"off",After adding piroxicam to the quenched CQDs,the fluorescence of CQDs was restored because piroxicam has a stronger binding ability with Cu2+to form a more stable complex.So it could remove Cu2+from the surface of CQDs,the fluorescent signal of the CQDs was"opened"again.The mechanism of the reaction was discussed and the reaction conditions were optimized.Under optimal conditions,the recovered fluorescence of CQDs was linearly related with the piroxicam concentration in the range 8.0×10-88 to 7.5×10-66 mol/L,the linear regression equation wasΔF=5.03×107c+12.28,the detection limit was 7.2×10-88 mol/L.The experiment provided a new fluorescence analysis method for the detection of piroxicam.4.Black bean CQDs（BS-CQDs）were synthesized by one-step hydrothermal method using green natural black beans as the carbon source,and the fluorescent properties and morphology were characterized.The results of TEM showed that the particle size of the BS-CQDs was about 10 nm and the distribution was uniform.XRD and FTIR showed that BS-CQDs were amorphous and with rich hydrophilic groups,such as-OH,-COOH and nitrogen functional groups,so the BS-CQDs had good water solubility.The UV-Vis and FL spectra showed that BS-CQDs had an obvious absorption peak at 274 nm,which was the characteristic UV-Vis absorption peak of CQDs.The BS-CQDs had a characteristic of excitation wavelength dependence,and the position of fluorescence emission peak moved with the change of excitation wavelength.It was found that in KCl-HCl buffer solution with pH=1.70,the fluorescence of BS-CQDs quenched by Ce（IV）but could be restored by cefixime.The recovered fluorescence of BS-CQDs was linearly related with the cefixime concentration in the range from 2.5×10-7to 1.5×10-55 mol/L,The linear regression equation wasΔF=2.65×107c+16.33.The establishment of the new system provided a new method for the determination of cefixime.It also provided a new idea for fluorescence analysis in pharmaceutical preparation. |
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