Investigating the Protein Secondary Structure at the Nanoscale using Infrared Nano-Spectroscopy

Scattering-type scanning near-field optical microscopy (s-SNOM) has become a key technology to study the chemical composition of organic materials at the nanoscale. This AFM-based technology exploits the strong confinement of light at the end of a sharp, metallic AFM tip to generate a nanoscale optical hotspot at the sample surface. Importantly, the amplitude and phase of the light within the optical hotspot is strongly influenced by the dielectric properties (absorption, reflectivity) of the sample directly below the tip. Phase and amplitude-resolved detection of the back-scattered radiation as function of position can therefore be used to extract the local optical properties at the sample surface with <10 nanometer precision. Utilizing broadband laser sources like a mid-infrared supercontinuum laser for tip illumination enables hyperspectral spectroscopic measurements with nanoscale spatial resolution. Embedded structural phases in organic semiconductors, biominerals, or biomolecules can now directly be visualized and characterized on the nanometer length scale. In this presentation we will introduce the basic principle of near-field microscopy and hyperspectral nanospectroscopy and address their impact and key applications in the field of organic materials