Fabrication of Flexible, Highly Reproducible, and Hydrophobic Surface-enhanced Raman Scattering Substrates Through Silver-Nanoparticle Inkjet Printing

We demonstrate a flexible, low-cost, and highly reproducible hydrophobic surface-enhanced Raman scattering (SERS) substrate produced by inkjet printing silver nanoparticles (Ag NPs) on a commercial overhead projector (OHP) film. Unlike a conventional Raman substrate such as glass or a silicon wafer, the OHP film is flexible, is easy and safe to handle, and has extremely low fabrication cost. Furthermore, our inkjet printing method is suitable for large-area fabrication of well-defined functional nanostructures. The prepared SERS substrate is a nanoplasmonic material owing to the presence of Ag NPs with hydrophobic surfaces due to their being coated with stearic acid (SA). The SERS activities of the OHP@Ag and SA-coated OHP@Ag substrates were verified experimentally using rhodamine B (RhB) as an analyte. The Raman band intensities of RhB deposited on the OHP@Ag substrate suggested obvious enhancement compared with those of the OHP film without Ag NPs. The SA-coated OHP@Ag substrate showed two-fold signal enhancement compared to the hydrophilic OHP@Ag substrate because of the hydrophobic condensation effect. The SERS detection signal for RhB had a relative standard deviation of 4.4%, revealing the excellent repro-ducibility of the substrate. Thus, this cost-effective and hydrophobic SERS flexible substrate can be used widely in SERS-based detection.