In situ nucleation and growth of silver nanoparticles in membrane materials: a controllable roughened SERS substrate with high reproducibility

A controllable roughened silver surface with high surface‐enhanced Raman scattering (SERS) activity and high reproducibility has been developed in this study. This silver surface was prepared by silver nucleation in polyelectrolyte multilayers (PEMs) and silver‐enlarged growth. First, the small Ag nuclei were synthesized by NaBH4 in situ reduction of Ag ions on a surface of PEMs. Then the small Ag nuclei formed were effectively enlarged by using a mixture of commercially available reagents named Li Silver. The optical properties and morphologies of the silver substrates have been investigated by ultraviolet–visible (UV–vis) spectroscopy and atomic force microscopy (AFM). The UV–vis and AFM results revealed that the small Ag nuclei separately appeared on the PEMs after NaBH4 in situ reduction. The size of the enlarged Ag nanoparticles can be easily controlled with the immersing cycle in Li Silver. 4‐Mercaptopyridine (4‐MPY) and Rhodamine 6G (R6G) have been used as Raman probes to evaluate the properties of the new SERS substrates. It has been found that the enhancement factor of R6G reached ∼109 after treatment in Li Silver. Reproducibility has been investigated using the SERS signal intensity at 1094 cm−1 of 4‐MPY. Signals collected over multiple spots within the same substrate resulted in a relative standard deviation (RSD) of 6.38%, while an RSD of 10.33% was measured in signals collected from different substrates.