Application Research Of Fluorescent Carbon Dots And Noble Metal Nanomaterials In Analysis And Detection

As a fluorescent nanomaterial with rapid research progress in recent years,carbon dots(CDs)are often used in the construction of fluorescence analysis methods because of their easy surface modification,resistance to photobleaching,wide source of raw materials,simple preparation and good photostability.Metal nanoparticles are widely used in the construction of colorimetric assays because of their good biocompatibility,large molar extinction coefficient and large specific surface area.With the continuous development of visual analysis,people combine the advantages of colorimetric and fluorescence analysis to build a variety of dual-signal analysis methods.This type of analysis method combines the high sensitivity of fluorescence analysis and the advantages of simple operation and low cost of colorimetric analysis.It can provide naked eye visual detection results,and the optical signal changes generated in the detection process can be detected by spectrometer,which helps to enhance the detection accuracy.It has great application prospects in biological monitoring,environmental analysis and other aspects.Based on the above,this work developed several analytical methods to detect ascorbic acid,chromium ion and alkaline phosphatase activity based on the unique optical properties of CDs and noble metal nanoparticles.The main work of this paper is as follows:1.Nitrogen-doped carbon dots(NCDs)were synthesized in a reactor by a one-step hydrothermal method,using O-phenylenediamine and ethylene glycol as precursors.The morphology,structure and fluorescence properties of N-CDs were characterized by transmission electron microscope(TEM),X-ray photoelectron spectroscopy(XPS)and so on.Based on the fluorescence enhancement effect of ascorbic acid(AA)on N-CDs and alkaline phosphatase(ALP)can catalyst the hydrolysis of L-ascorbic acid-2-phosphate(AA-2P)to produce AA,a highly sensitive fluorescence analysis method for the detection of AA and ALP was developed.The concentration of AA shows a good linear relationship with the fluorescence signal in the range of 0-150?mol/L and the detection limit is 0.52?mol/L.The fluorescence signal has a good linear relationship with the concentration of ALP in the range of 0-70 U/L and the detection limit is 0.68 U/L.The method has been successfully applied to the detection of ALP in human serum.2.A dual-signal visualization method for the detection of chromium ion was developed by combining fluorescent carbon dots with glutathione modified gold nanoparticles(GSH-AuNPs).GSH-AuNPs can quench the fluorescence of carbon dots based on the internal filtering effect(IFE).The presence of Cr³⁺can induce specific aggregation of GSH-AuNPs,thus a red shift of the SPR absorption peak of GSH-AuNPs and a"red-blue"color change take place.This process destroys the fluorescence quenching of carbon dots by GSH-AuNPs,which induce the fluorescence recovery of carbon dots.The fluorescence signal of the method has a good linear relationship with the concentration of Cr³⁺in the range of 0.5-70?mol/L and the detection limit is 0.37?mol/L.The colorimetric signal shows a good linear relationship with the concentration of Cr³⁺in the range of 2-50?mol/L and the detection limit is 0.30?mol/L.The dual-signal analysis showed good selectivity for Cr³⁺and was successfully applied to the detection of Cr³⁺in lake water samples.3.A dual-signal method for the detection of ALP was constructed by combining carbon dots and gold@silver nanoparticle etching.In this system,Au@Ag nanoparticles can quench the fluorescence of the carbon dots.ALP can catalyze the substrate AA-2P to produce AA,which can reduce the potassium iodate(KIO₃)in the detection solution to produce iodine monomers(I₂).I₂ oxidize the etched silver shell of Au@Ag NPs,thus a red shift of the SPR absorption peak and a"yellow-brown"color change take place,coupled with the fluorescence recovery of carbon dots.The fluorescence signal shows a good linear relationship with the concentration of ALP in the range of 0-100 U/L and the detection limit is 0.20 U/L.The colorimetric signal shows a good linear relationship with the concentration of ALP in the range of 5-100 U/L and the detection limit is 1.88 U/L.The dual-signal method shows good selectivity for ALP and can be used for the detection of ALP in human serum.