Probing Denaturation of Protein A via Surface-Enhanced Infrared Absorption Spectroscopy

Abstract

We apply surface-enhanced infrared absorption (SEIRA) spectroscopy to monitor the denaturation process of a surface-bound protein A monolayer. Our proposed platform relies on a plasmonic metasurface comprising different spatial subregions (“pixels”) that are engineered to exhibit different resonances covering the infrared region of the electromagnetic spectrum that is matched to the vibrational modes of the Amide groups. Specifically, we are able to determine changes in the Amide I and Amide II vibration coupled modes, by comparing the SEIRA reflectance spectra pertaining to the native state and a denatured state induced by a pH variation. In particular, we observe some evident red-shifts in the principal Amide I mode and the Amide II vibration coupled modes (attributable to the breaking of hydrogen bonds), which result in insurmountable barriers for refolding. Thanks to the strong field localization, and consequent enhancement of the light-matter interactions, our proposed sensing platform can operate with extremely small amounts of an analyte, with an estimated detection limit of about 3 femtomoles of molecules.

Numerical investigation of plasmonic bowtie nanorings with embedded nanoantennas for achieving high SEIRA enhancement factors

“…Further, Gao et al [69] have developed a generalized classical model of SEIRA spectroscopy that shows that mid-IR surface plasmon resonances can be used for detection of vibrational bands. SEIRA spectroscopy has also been incorporated to monitor protein denaturation in the infrared regime using engineered plasmonic metasurfaces [70]. In a latest report by Najem et al [71] enhanced infrared sensing is demonstrated using aluminium nanostructured bowties on a metal-insulator-metal (MIM) platform.…”