Application Of Nano-gold Enhanced Optical Effect In The Detection Of Food Hazards

Nanoprobes based on precious metal nanomaterials have excellent performance in heavy metal detection and organic pollutant detection due to their high sensitivity,visible to the naked eye,non-destructive real-time detection and low detection cost.However,due to the complexity of the detection method and the low detection sensitivity,this paper uses the optical effect of gold nanoparticles to develop a colorimetric and fluorescent sensor,which successfully detects the lead ion(Pb²⁺)in the food matrix and the organic pollutant Rhodamine 6G(R6G).The main work is as follows:(1)A gray system based on the principle of complementary colors was established for the sensitive and specific naked eye detection of Pb²⁺in complex food matrices by using glutathione(GSH)modified gold nanoparticles(AuNPs)as an indicator.The gray system is prepared by mixing the purple-red GSH modified AuNPs(AuNPs-GSH)and the blue-green sulfonated pigment green 7(SPG7),and is named SPG7/AuNPs probe.In the presence of Pb²⁺,the strong chelation of Pb²⁺with GSH can trigger the aggregation of AuNPs,leading to the color activation of SPG7.Therefore,the ratio of the absorbance at 523 nm to the absorbance at 628 nm(A_{523 nm}/A_{628 nm})can be used to quantitatively detect Pb²⁺,and the detection limit of the probe is 0.33?g/L.Moreover,this probe exhibits promising practical applications in real preserved egg samples with recoveries of 89.2%to 107.5%and relative standard deviations(R.S.D.)in the range of 0.28%to 2.12%.(2)The surface of AuNPs was coated with mercapto-poly-N-isopropylacrylamide(HS-PNIPAM)to synthesize polymer-coated core-shell nanoparticles(AuNPs-HS-PNIPAM),which explained the surface-enhanced fluorescence effect(SEF)mechanism and realize the detection of R6G molecules.In this experiment,AuNPs is the necessary metal core,and HS-PNIPAM is the temperature-responsive elastic shell.The elastic shell layer ensures a certain distance between the R6G and the surface of the nanoparticle.A part of R6G is in the local electric field of AuNPs,thereby enhancing the fluorescence emission of R6G molecules.When the natural frequency of 82 nm AuNPs matches the emission wavelength of R6G,and the thickness of HS-PNIPAM is7.7 nm,the fluorophore has a higher plasma-enhanced fluorescence efficiency.When R6G droplets exist,as the temperature of the droplets gradually decreases(60°C-28°C),the proximity of R6G to the surface of AuNPs leads to a gradual increase in the energy transfer efficiency from AuNPs to R6G,so the intensity of the Rayleigh scattered light of AuNPs gradually decreases.Here,we ignore the energy provided by the fluorophore to the AuNPs.