Large-scale Ag nanoislands stabilized by a magnetron-sputtered polytetrafluoroethylene film as substrates for highly sensitive and reproducible surface-enhanced Raman scattering (SERS)

Fabrication of surface-enhanced Raman scattering (SERS) nanostructures with both high sensitivity and spectral reproducibility, which are key requirements for routine SERS quantitative (sensing) applications, is a great challenge. Here we report on the multilayered design of SERS-active substrates formed by uniform Ag nanoislands stabilized by a magnetron-sputtered polytetrafluoroethylene (msPTFE) film of nanometre thickness. The preparation of large scale (similar to 20 cm(2)) nanostructures with long (Bmonths) time stability was fast (similar to minutes), cheap and repeatable. SERS performance of our substrates was subsequently improved by step-by-step optimisation of the fabrication procedure and introduction of the additional silver layer, separating the supporting glass from the msPTFE film, which contributed to the total enhancement factor by another order of magnitude. Such substrates provided high SERS sensitivity with a SERS enhancement factor of about 2 orders of magnitude larger than commonly reported in the literature for Ag nanoislands grown directly on glass. The limits of detection were determined as similar to 1 x 10(10) M, 1 x 10(-7) M and 1 x 10(-6) M for testing analytes methylene blue (MB), 5,10,15,20-tetrakis(1-methyl-4-pyridyl) porphyrin (H2TMPyP) and cysteine, respectively. SERS substrates showed excellent spectral reproducibility both across a single substrate and different substrate batches. The relative standard deviation (RSD) of the SERS signal did not exceed 20% for different concentrations of MB and H2TMPyP, respectively. Therefore, Ag nanoislands stabilized by the msPTFE film are due to high sensitivity, stability and excellent spectral reproducibility very promising substrates for SERS biomolecular quantitative (sensing) applications.