Detection Of Melamine Based On The Fluorescence Resonance Energy Transfer And The Inner Filter Effect Of Metal Nanoparticles

This study was granted by “The Applications of Advanced Materials in FoodSafety Analysis”, a Talent Introduction Fund of Agriculture Division of JilinUniversity. Detection of melamine using optical properties of metal nanoparticles(MNPs) was investigated.In this thesis, based on the fluorescence resonance energy transfer (FRET)/innerfilter effect (IFE) between gold nanoparticles (AuNPs, absorber) and dye/quantumdots (QDs, fluorophore), two sensitive, rapid and simple fluorescent analyticalmethods for melamine were developed and further applied in practical detection.The study included the following two aspects:(1) A fluorescent “turn-on” sensor for melamine detection was developed basedon FRET between Rhodamine B (RB) and citrate-stabilized AuNPs. RB could beattached to the surface of the AuNPs by electrostatic interaction and the fluorescenceemission of RB was obviously quenched via FRET, resulting in a fluorescence“off-state”. Upon addition of melamine, its molecules could strongly bind to thesurface of the AuNPs by ligand change, releasing the adsorbed RB molecules.Furthermore, melamine can induce the aggregation of the AuNPs, reducing theoverlap between the fluorescence emission spectrum of RB and the absorptionspectrum of the AuNPs. The two factors notably inhibited FRET, making theFRET-decreased fluorescence emission of RB markedly recovered and achieving afluorescent “turn-on” state. Under the optimal conditions, a good linear relationshipbetween the fluorescence recovery degree of RB and melamine concentration wasobtained in the range of5~1000μg L-1, R2=0.99, and the limit of detection (LOD)was0.18μg L-1. The method was successfully applied to detect melamine in liquidmilk and powdered infant formula with a recovery of95.9%-102.2%.(2) A fluorescent analytical method for melamine detection was established based on IFE of citrate-stabilized AuNPs on the fluorescence of TGA-capped CdTeQDs. The fluorescence of the CdTe QDs was significantly quenched via the efficientIFE of the AuNPs. But if melamine and the AuNPs were mixed at first and then theCdTe QDs were added, melamine could induce the aggregation and correspondingabsorbance change of the AuNPs, which then inhibited IFE and recovered theIFE-decreased fluorescence of the CdTe QDs. Under the optimum conditions, thefluorescence recovery degree of the CdTe QDs exhibited a good linear correlation tomelamine concentration in raw milk in the range from100~1100μg L-1and the LODwas20μg L-1. The method was successfully used for detecting melamine in raw milksamples with satisfying recovery and repeatability with a recovery of103%-104%.