Methods Research Of Upconversion Fluorescence Technology In Trace Hazard Residual Detection In Milk

The rapid progress of dairy industry has led to several concerns over its products quality and safety.Maintaining good quality and safety of raw milk plays a key role in the development of dairy industry.The raw materials responsible for milk adulteration are affected by chemical and microbiological pollution due to the presence of trace organic and inorganic species,thus influencing the quality of milk and dairy products.Despite the availability of highly sensitive and reliable detection tools for these species,it accompanies several shortcomings including complications in operation and costly instrumentation.Therefore,it is of great significance to design simple,quick and sensitive methods for trace organic and inorganic species to ensure milk safety and consumers health.In recent years,upconversion fluorescence detection technology has gained considerable interest due to its unique upconversion luminescence,high specificity,sensitivity,simplicity and wide utility.Therefore,new methods based on upconversion luminescence were required for the detection of trace harmful substances in milk.This goal was achieved by analyzing and discussing the main pattern and the basic principle of upconversion fluorescence detection,upconversion fluorescence nanoparticle synthesis and finally developing a series of new detection methods for rapid and sensitive detection of trace harmful substances in milk.The specific research contents are as follows:1.Upconversion fluorescence detection method for the determination of tetracycline?TET?residues in milk.The aptamer-magnetic nanoparticles?Apt-MNPs?and the complementary DNA-UCNPs?cDNA-UCNPs?conjugates were prepared at first.They formed the complex of MNPs-Apt-cDNA-UCNPs by hydrogen bonding With TET addition,the aptamer preferentially bound with TET and caused the dissociation of some cDNA;and the liberation of some cDNA-UCNPs.After magnetic separation,the fluorescence intensity of the detection system decreased.Under the optimal conditions,a wide linear detection range from 0.01 to 100 ng/mL was achieved,with a detection limit of 0.0062 ng/m L for detecting TET.The proposed method was successfully applied to measure TET in contaminated samples with the recovery rate in the range of 98.2%-101.7%,variation coefficient in the range of 0.1%-3.2%.Results showed that the proposed UCNPs biosensor offers an efficient,specific,and simple approach for the detection of TET in milk.2.Upconversion fluorescence detection method for the determination of mercury ion(Hg²⁺)residues in milk.In this study,a turn-on nanosensor was developed based on the fluorescence resonance energy transfer?FRET?between aptamers functionalized upconversion nanoparticles?Apt-UCNPs?and complementary DNA functionalized gold nanoparticles?cDNA-GNPs?.In the absence of Hg²⁺,FRET between UCNPs and GNPs occurred owing to the specific matching between aptamers and cDNA,result in the fluorescence quenching of UCNPs.In the presence of Hg²⁺,aptamers foldback into a hairpin structure due to the stable binding interactions between Hg²⁺and thymine,leading to the release of GNPs from UCNPs,result in the quenched fluorescence restoration.Under the optimized conditions,the nanosensor achieved a linear detection range of 0.2-20?M and a low detection limit of 60 nM.Meanwhile,it showed good selectivity and has been applied to detecte Hg²⁺in milk samples with recovery rate in the range of 95.18%-103.77%,variation coefficient in the range of 2.03%-8.12%.3.Upconversion fluorescence detection method for the determination of fluorion?F^-?residues in milk.The natural chemical curcumin served as specific recognition element and mixed with UCNPs to make a nanosystem.In this nanosystem,the absorption peak of curcumin shows bathochromic shift when F^-was added,causing an upconversion fluorescence quenching at 546 nm and 657 nm through inner filter effects?IFE?,while the upconversion emission at 758nm and 812 nm remained unchanged.Thus,the fluorescence ratio I₅₄₆/I₇₅₈58 was inversely proportional to F^-concentration.Under the optimized conditions,the developed UCNPs-curcumin mixed system achieved the ratiometric fluorescence sensing towards F^-in the linear range of 5–200?M,with the detection limits as low as 5?M?ca.0.1 ppm?.The developed nanosystem also has high selectivity and specificity.Furthermore,this method showed promising practical applications in spiked milk samples with recoveries of 80.34%to 119.92%and variation coefficient in the range of 1.97%-22.11%,which confirmed its great potential in harmful substance detection.