A facile route of microwave to fabricate PVA-coating Ag nanofilm used as NIR-SERS active substrate

Abstract

Surface-enhanced Raman spectroscopy (SERS) is a very sensitive and selective technique for detecting surface species. Recently, SERS has been increasingly employed in the study of biological macromolecules, from DNA and peptides to whole proteins, and cells. However, visible laser sources usually employed in SERS detections always lead to photochemical reactions as well as intensive fluorescence emission from the biological samples. A way to avoid these questions is the employment of near infrared (NIR) laser excitation; thus, it demands the appropriate designs of NIR-SERS substrates in order to obtain the maximum enhancement of the Raman signals from biological analytes. In this work, we demonstrate the fabrication of a new NIR-SERS substrate of polyvinyl alcohol (PVA) coating Ag nanofilms (PVA-coating Ag nanofilm) using a simple and low-cost microwave strategy. The experimental data show that, the plasmon resonance band of the PVA-coating Ag nanofilm is in the region of 400–900nm, and the maximum center is at ∼780nm, which matches well with the 785nm laser excitation employed in this work. With the NIR-SERS detections of hematin and hemoglobin molecules adsorbed on this PVA-coating Ag nanofilm, one can see that the NIR-SERS activity and spectroscopy reproducibility of this NIR-SERS substrate are all perfect. By using of the tested molecule of hematin, the PVA-coating Ag nanofilm shows a high enhancement factor (EF) of ∼107. As the fabrication process of this NIR-SERS substrate is very simple and inexpensive, this method may be used in large-scale preparation of SERS substrates that have been widely applied in Raman analysis. Especially, this PVA-coating Ag nanofilm can also be served as a novel NIR-SERS substrate in biochemical analysis due to its good NIR characteristics.