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 gm by H2O2 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 H2O2, which means the available amount of H2O2 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 mu M (R-2=0.989), with a limit of detection CLOD) of 8.51 nM. Moreover, the proposed highly selective method is fully capable of rapid, separation-free detection of melamine in milk powder. (C) 2015 Elsevier B.V. All rights reserved.