Efficient conversion and highly sensitive detection of PAEs in milk based on hydrazinolysis reaction and hydrogen bonding using SERS technique.

Background: Phthalate esters (PAEs), a diverse group of plasticizers with reproductive and developmental toxicity, have their residues in milk packaging increasing with lipid solubility as the storage time elapses, thereby posing a serious threat to human health. Detection methods based on chromatography and mass spectrometry are technically mature, with high sensitivity. However, their sample pretreatment is complicated, the instruments used are expensive, and they have high environmental requirements, making them unsuitable for on-site detection.

Results: The SERS technique is more portable, rapid, highly sensitive, and low-cost in substance detection. We used Au@Ag@IP6 NPs as the SERS substrate to conduct precise quantitative detection of PAEs residues in milk. In this method, PAEs first need to react with hydrazine hydrate to generate phthalhydrazide. Taking advantage of the strong metal complexing ability of IP6, an ultra-thin coating is formed on the silver shell. Through the hydrogen bonding effect between phthalhydrazide and IP6, phthalhydrazide is tightly adsorbed in the "hot spots" among Au@Ag@IP6 NPs, thus obtaining an extremely enhanced signal, enabling rapid detection within 15 min. This method elaborated the preparation process of Au@Ag@IP6 NPs, verified the stability of the substrate, optimized the reaction conditions of PAEs, and conducted spiked tests on milk. The spiked recovery rate ranges from 85 % to 115 %, and the relative standard deviation (RSD) value is less than 10 %.

Significance: This scheme can achieve rapid detection of plasticizers in milk within 15 min by uniformly converting various PAEs molecules into phthalhydrazide and utilizing the strong adsorption of nanoparticles to phthalhydrazide. The synthesized nanoparticles have a strong hydrogen bonding effect with most substances containing the N element, and it is expected that this scheme can be extended to the detection of other systems with high nitrogen content.