Two-step-route to Ag-Au nanoparticles grafted on Ge wafer for extra-uniform SERS substrates

A two-step galvanic displacement reaction was employed to synthesize Ag-Au nanoparticles grafted on Ge wafer using different equilibrium potentials. The Ge wafer was employed to reduce silver ions and grow Ag nanoparticles first, and then to reduce gold ions and to grow Au nanoparticles between the gaps of Ag nanoparticles. When they were employed as SERS substrates to detect 200 random spots, the lowest relative standard deviation (RSD) to our knowledge, of less than 7% was obtained by using Rhodamine 6G (1 × 10^-9 M) as probe molecules in the aqueous detection. Crystal violet solution (1 × 10^-8 M) was also detected with an ultra low RSD of less than 8%. The result of the electric field distribution by the finite difference time domain simulation further explained the distinguished sensitivity and uniformity of these substrates. The high uniformity and reproducibility of this substrate may benefit quantitative surface enhanced Raman scattering (SERS) detection in the field of biology in future.