A simple method for preparation of Ag nanofilm used as active, stable, and biocompatible SERS substrate by using electrostatic self-assembly.

A new SERS-active Ag nanofilm on the surface of a glass slide has been prepared by a low-cost electrochemical strategy using polyvinyl alcohol (PVA) at a proper voltage. The two-dimensional morphology of the Ag nanofilm has been examined by scanning electron microscopy (SEM). The average size of the aggregated particles on the surface of the Ag nanofilm is up to ca. 200+/-50 nm, which is much larger than that of PVA-protected Ag colloidal nanoparticles (PVA-Ag CNPs, 45+/-8 nm). Meanwhile, many nano-scale regions with average sizes of ca. 300+/-50 nm are formed between the adjacent Ag nanoparticles. By the SERS measurements of human serum (HS) and hemoglobin (Hb), this Ag nanofilm is shown to be an excellent SERS substrate with good stability and biocompatibility. As the fabrication process of this SERS substrate is simple and inexpensive, this method may be used in large-scale preparation of substrates that have been widely applied in Raman analysis. In addition, this SERS-active Ag nanofilm can serve as a novel SERS substrate in biochemical analysis due to the biocompatibility.