Preparation Of The Label-free SERS Sensor And Its Application In The Rapid Detection Of Melamine And Penicilloic Acid In Milk Products

In recent years,more and more foods(especially,milk products)have been illegally adulterated with the non-food chemicals by some producers owing to profits,which do harm to the public health.So it is crucial to develop a rapid and simple method of monitoring the forbidden chemicals in milk products.Surface-enhanced Raman scattering(SERS)technique has become a powerful analytical tool for the rapid detection of chemical and biological species due to high sensitivity,narrow spectroscopic fingerprint,nondestructive nature and easy sample preparation.In this work,a label-free SERS strategy based on silver-coated gold nanoparticles(Au@Ag NPs)was developed for rapid detection of melamine(MA)and penicilloic acid(PA)in milk products.It has been demonstrated that core size and shell thickness of Au@Ag NPs are two critical variants affecting enhancement of Raman signals by coupling of two plasma resonance absorption.The Au@Ag NPs with 26-nm core and 9-nm Ag shell exhibit excellent Raman enhancement,in particular,upon the formation of hot spots by NPs aggregation induced by interaction between target molecules and Au@Ag NPs.Compared to the early studies limited to laboratory settings,our analytical approach is simple(without sample pretreatment),less time-consuming and inexpensive.The limit of detection(LOD)of MA in liquid milk,yogurt and milk powder is 0.750 ppm,respectively.Meanwhile,the LOD of PA is 3.00 ppm,3.00 ppm and 4.00 ppm in liquid milk,yogurt and milk powder,respectively.Good recoveries were also obtained from milk products spiked with MA or PA.The label-free SERS technique offers a potential for the on-site monitoring of chemical contaminants in milk products.