Adaptive silver films for bio-array applications

Summary form only given. The adaptive property of e-beam evaporated silver films has been studied and employed for protein sensing with surface-enhanced Raman scattering (SERS). Our approach for sensing proteins is based on adaptive silver films (ASFs); the method allows fine nanostructure rearrangement under protein deposition that makes it possible to soft-adsorb proteins on the metal surface and to form aggregates of nanoparticles which are optimal for SERS. We demonstrate that adaptive nanostructured films can be used for the observation of differences in SERS spectra of recombinant human insulin and insulin lispro at sub-monolayer protein surface densities and provide macroscopic enhancement factor of about 3×10⁶ . Since human insulin and its analog have the same set of side chains and differ only in conformational states, the observed difference indicates the preservation of the conformational state with the use of adaptive metal substrates. Direct, label-free detection of antibody-antigen binding at a monolayer protein concentration has been also demonstrated, using SERS detection on adaptive silver films. This includes evidence of distinct SERS spectral changes upon antigen-antibody binding and independent biochemical sandwich assay validation studies, which confirm that antibodies retain binding properties on ASFs. It is shown that proteins stabilize the ASFs and restructure them so that proteins can preserve their binding activity. We demonstrate the ability to employ various detection methods with one substrate, including label-free SERS, chemiluminescence, fluorescence, and further analysis of protein spot retrieved from the surface.