Fluorescent Upconversion Nanoparticles And Their Application In The Analysis Of Pesticides Residues In Traditional Chinese Medicines

As the treasure of China,traditional Chinese medicines?TCMs?have attracted more and more attention around the world for their long-term clinical practice and reliable therapeutic effect.However,the safety and efficiency of TCMs can be decreased by pesticide residues,which greatly weakens the competitiveness of TCMs in the international market.Therefore,it is of great importance to develop sensitive,rapid and low-cost methods for analyzing pesticide residues in TCMs for ensuring the quality and safety of TCMs and promoting the internationalization of TCMs.Upconversion nanoparticles?UCNPs?are lanthanide-doped inorganic nano-materials,which are capable of converting near-infrared excitation to ultraviolet or visible emission.In comparison with traditional fluorescent?FL?probes such as organic dye and FL protein,UCNPs possess unique physicochemical features including large anti-Stokes shifts,long-term chemical stability,negligible photobleaching and low toxicity.Under near-infrared excitation,UCNPs are free of autofluorescence interference from various sample matrixes,which provides low background signal and high signal-to-noise ratio.UCNPs have attracted extensive attention in biomedicine,and showed great application potential in biosensing,drug delivery and bioimaging.In this study,using UCNPs as FL probes,we designed two FL methods based on photoinduced electron transfer?PET?and fluorescence resonance energy transfer?FRET?for analyzing pesticide residues in TCMs.1.A fluorescent method based on tyrosinase-mediated photoinduced electron transfer for the analysis of organophosphorus pesticideA tyrosinase-mediated PET system was constructed for organophosphorus pesticides?OPs?analysis by using dopamine-functionalized UCNPs as FL probes.Dopamine quinone was produced by tyrosinase-mediated oxidation of dopamine on the surface of UCNPs,which acted as electron accepter to quench the FL emission of UCNPs.With the addition of OPs,less dopamine quinone was produced due to the inhibited activity of tyrosinase.Thus,stronger FL emission could be observed in the presence of OPs.Chlorpyrifos was used as a model analyte to investigate the feasibility of the FL method for the analysis of OPs.Under the optimal conditions,chlorpyrifos can be analyzed within a wide range of 1.0-1000 ng mL^-1,with a detection limit of 0.38 ng mL^-1?3??.Some other groups pesticides,including organonitrogen pesticide,organochlorine pesticide and chloronicotinyl insecticide all showed negligible interference.And the method can exclude interference from common matrix substance existing in plant samples.The proposed method was successfully used to analyze chlorpyrifos spiked in Balloonflower and Angelica with acceptable recovery values of 95.4-120.0%.It exhibits some advantages like low cost,high sensitivity and free of autofluorescent interference and photobleaching.The successful application in TCMs analysis indicates its application potential for real samples.2.A label-free fluorescent method based on fluorescence resonance energy transfer for the analysis of cyanophoric pesticidesA label-free FL method was constructed for the analysis of cyanophoric pesticides based on FRET between UCNPs and Au nanoparticle?AuNPs?.When negatively charged AuNPs were added into positively charged amino-modified UCNPs,AuNPs were adsorbed onto the surface of UCNPs by electrostatic interaction.Then the FL emission of UCNPs was quenched by AuNPs via FRET process.In the presence of cyanophoric pesticides,the pesticides could bind to the surface of AuNPs via Au-N=C metal-ligand coordination,which removed the citrate ions capped on the surface of AuNPs and induced the aggregation of AuNPs.Accordingly,the FL intensity of UCNPs was recovered due to the inhibition of FRET.Acetamiprid,fenpropathrin and chlorothalonil were used as model analytes to investigate the feasibility of the FL method for the analysis of cyanophoric pesticides.Under the optimal conditions,acetamiprid,fenpropathrin and chlorothalonil were analyzed within the wide range of 0.1-100 ng mL^-1,1.0-100 ng mL^-11 and 0.1-50 ng mL^-1,with detection limits of 0.015 ng mL^-1,0.24 ng mL^-1 and 0.011ng mL^-1?3??,respectively.The whole analysis procedure could be accomplished within6 min.This method was free of probe labelling and provided a platform for the analysis of other cyanophoric pesticides.It also possessed some merits,such as simple operation,short time,high sensitivity and low cost.The proposed method was successfully used to analyze acetamiprid spiked in Lanceolata,Angelica dahurica,and Astragalus with acceptable recovery values of 76.0%-120.0%,showing its potential practical application.In summary,based on the unique optical properties of UCNPs,two FL methods were constructed for the analysis of pesticide residues in TCMs.Superior to traditional FL probes,UCNPs exhibit large anti-stokes shift and high photostability.Therefore,these FL methods based on UCNPs were free of autofluorescent interference and photobleaching.Combining with PET,FRET and enzyme inhibition strategy,these methods exhibited some advantages like low cost,simple operation,high sensitivity and satisfying reproducibility,providing a novel technical platform for guaranteeing safety of TCMs.