Adaptive SERS substrates for protein sensing

Adaptive surface-enhanced Raman scattering (SERS) substrates exhibit unique properties which make them well suited for SERS studies of proteins on surfaces. Specifically, adaptive silver films (ASFs) allow nanoscale restructuring of metal particles during protein deposition which yields a three-fold benefit of soft protein adsorption, protein-metal complex stabilization, and increased SERS signal. In this work ASF fabrication and characterization methods are introduced, with special attention paid to characterization methods that provide insight into the adaptive nature of the substrates, such as UV-vis spectrophotometry, field-emission scanning electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. These ASF substrates show SERS enhancement factors in the range of 106 for an area-averaged signal, and have been successfully used for sub-monolayer protein detection. The addition of a thick metal layer in the ASF fabrication structure typically increases the SERS signal by a factor of four or five. Finally, several examples of current SERS protein studies using ASF substrates are provided.