Simultaneous enzymatic and SERS properties of bifunctional chitosan-modified popcorn-like Au-Ag nanoparticles for high sensitive detection of melamine in milk powder

In this work, we suggest a chitosan-modified popcorn-like Au–Ag nanoparticles (CSPNPs) based assay for high sensitive detection of melamine , in which CSPNPs not only provide with an intrinsic peroxidase-like activity but also act as surface enhanced Raman scattering (SERS) substrates. CSPNPs can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H 2 O 2 to the charge transfer complex (CTC), which contributes to a tremendous surface-enhanced resonant Raman scattering (SERRS) signals with 632.8   nm laser excitation. The target molecule melamine can generate an additional compound with H 2 O 2 , which means the available amount of H 2 O 2 for the oxidation of TMB reduced. Correspondingly, the SERRS intensity of CTC is decreased. The decreased Raman intensity is proportional to the concentration of melamine over a wide range from 10   nM to 50   μM ( R 2 =0.989), with a limit of detection (LOD) of 8.51   nM. Moreover, the proposed highly selective method is fully capable of rapid, separation-free detection of melamine in milk powder.