Highly sensitive Ag/PMMA SERS substrate with dense and uniform nano-forest structure for the detection of melamine in milk

In this paper, a large-area uniform nano-forest structure was produced on PMMA support by simple plasma treatment, and a highly sensitive Ag/PMMA SERS substrate was obtained by a thermal evaporation method. SEM images reveal the Ag/PMMA substrate featured densely distributed nano-trees containing lots of branches. FDTD simulation confirmed the gaps both on the top surface and in the body of the nano-forest were all effective hot spots, which could confine intense local electric field. By using crystal violet (CV) as the probe molecule, it was demonstrated the Ag-50/PMMA substrate prepared with a deposition time of 50 min could easily detect 10-10 M CV, and the enhancement factor (EF) was calculated to be 5 x 107. The Ag-50/PMMA substrate exhibited good uniformity and reproducibility with a relative standard deviation (RSD) of 3.6% and 7.8% respectively. Both the successful detection of melamine in milk with a concentration of 0.001 ppm, much lower than the permitted amount of melamine in milk, and the desirable accuracy exhibited in the recovery rate experiments demonstrated the satisfactory detection ability of the Ag-50/PMMA substrate in the real application. The high performance of the proposed SERS substrate ensured its great potential for applications in the field of food surveillance.