IR ellipsometry of silk fibroin films on Al nanoislands

Infrared spectroscopic ellipsometry (IRSE) is a powerful tool for the characterization of various types of organic and inorganic films. In application to protein films, IRSE can be utilized to detect structural changes, orientation of specific group, etc. Because of sensitivity, enhanced IRSE will be very useful to study protein thin films. Here we show that fibroin films on Al mirror display surface-enhanced infrared spectroscopic ellipsometry (SEIRSE). AFM data indicate that nanoislands on the Al mirror are responsible for the plasmon-enhanced mechanism. SEIRSE for fibroin films shows non-uniform enhancement across the spectrum. Possible mechanisms of such enhancement are provided. Evidently, as proposed previously, at least two mechanisms, the electromagnetic (EM) and chemical, are expected to contribute to the enhancement. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)