The Study On Using Fluorescent Probe To Detect Melamine In Raw Milk

Quantum Dots，as a typical representative nano-material, because of goodoptical, electrical properties, magnetism properties and so on, QDs have been widelyapplied in the fields of environment, medicine, biology, etc and been widelyconcerned by researchers. Melamine, as an important organic chemicalproduction, was used for production of multipurpose melamine-formaldehyderesins. The nitrogen level can reach up to66%. It is not approved for use as a feedor food additive. However, due to its high nitrogen level （66%nitrogen by mass）,melamine has been added illegally into infant formula to artificially distort their crudeprotein content. Melamine has low oral acute toxicity, but the combination ofmelamine with cyanuric acid leads to the formation of insoluble crystals in thekidneys. The chronic administration of high concentrations of melamine can inducerenal failure and even death, especially in babies and children. A certain maximumlevel of melamine ingestion is officially fixed in foods, e.g.,2.5ppm in the USA andEU, and1.0ppm for infant formula in China. To date, the standard approaches ofdetection melamine in raw milk have HPLC, GC-MS, HPLC-MS, and so on. In thispaper, QDs was used as fluorescent probe to detect melamine in raw milk. Theobvious merits provided by proposed methods, such as simplicity, rapidity, low costand high sensitivity would make it promising for on-site screening of melamineadulterant in milk products. Moreover, the possible experiment mechanism involvedin the detection of melamine was also discussed and verified.Water-soluble CdTe quantum-dots of different sizes capped with thioglycolicacid （TGA-CdTe QDs） were synthesized via a microwave-assisted method. It wasfound that melamine could quench the fluorescence emission of TGA-CdTe QDs inaqueous solution. The fluorescence intensity of TGA-CdTe QDs versus melamineconcentrations gave a linear response according to the Stern-Volmer equation. Basedon this, a novel method for the determination of melamine has been developed. Underoptimum conditions, the proposed method has been successfully used to detect melamine in the liquid milk with a detection limit of0.04mg·L^-1, and the wholeprocess including sample pretreatment could be accomplished within30min. Theobvious merits provided by this method, such as simplicity, rapidity, low cost andhigh sensitivity would make it promising for on-site screening of melamine adulterantin milk products.A simple, rapid and sensitive fluorescent assay for melamine has been developedbased on inner filter effect （IFE） of gold nanoparticles （AuNPs） on the fluorescence ofCdS quantum dots （QDs）. When CdS QDs capped with L-Cys was mixed withcitrate-stabilized AuNPs, the fluorescence of CdS QDs was significantly quenched viathe IFE of AuNPs. With the presence of melamine, melamine could induce theaggregation and corresponding absorbance change of AuNPs, which then resulted inthe recovery of IFE-decreased emission of CdS QDs. Under the optimum conditions,the detection limit for melamine in raw milk was0.02mg·L^-1. The application of thismethod in samples of melamine-spiked raw milk suggested a recovery between103%and104%.