Low-cost, mass-producible nanostructured surface on flexible substrate with ultra-thin gold or silver film for SERS applications

Surface Enhanced Raman Spectroscopy has emerged as a powerful analytical technique for fingerprint recognition of molecular samples with high sensitivity. The Surface Enhanced Raman Scattering (SERS) effect has been extensively studied for the past few decades. However, only recently the commercialization of portable Raman spectrometers has taken SERS a step closer to real-world applications. Swift and convenient testing of analytes for point-of-care, environmental as well as food quality control and safety applications, is very lucrative. This can be realized with the use of low-cost, mass producible and environmentally friendly SERS active substrates in combination with portable Raman spectrometers. In this study, we demonstrate one approach to accomplish such a SERS-active substrate using nanostructured latex coated paperboard as a base substrate. The nanostructure is accomplished by applying a reverse gravure coater in combination with a short-wavelength infrared (IR) heater. The whole process is easily up-scalable. The SERS functionality is then obtained by physical vapor deposition of an ultra-thin layer of Au or Ag. The surface nanostructure was confirmed by atomic force microscopy, showing an additional nanoscale graininess after the deposition of Au or Ag. The successful metal deposition was confirmed by X-ray photoelectron spectroscopy and deposition homogeneity was also analyzed. To confirm the SERS effect, two model compounds; crystal violet and rhodamine 6G were tested in the concentration range of 1–1000 μM. The results confirmed that the nanostructured, flexible, paper-based substrate can perform as a SERS-active substrate with negligible background noise.