Accessing chemically-specific information in complex materials with nanoscale optical spectroscopy

Optical spectroscopy has been used extensively to obtain structural and chemical information, and has provided a wealth of knowledge about biological macromolecular organization and the mechanics of biological processes. Unfortunately, diffraction limits the spatial resolution to hundreds of nanometers or micrometers, preventing direct observation of important biological structures and their complex hierarchical organization, which spans length scales from nanometers to millimeters. In particular, the ability to directly access information about the secondary structure of proteins, which is important to the prediction of tertiary or quaternary structure and overall function (biological problems) or property (materials applications), is difficult to achieve due to a lack of chemically-specific, nanometer-scale probes.

Here, I discuss the development of scattering-scanning near-field optical microscopy (s-SNOM), a combined atomic force microscopy/optical technique, and its application to understanding heterogeneity in complex soft matter systems. In s-SNOM, a scanning probe tip acts as an antenna to locally enhance and scatter light and access nanoscale optical information. In combination with IR and Raman vibrational spectroscopic techniques, we can probe biological and biomaterials systems and investigate nanometer-scale structure and its relation to functional and engineered properties. Furthermore, this approach is compatible with both dry and aqueous environments. The combination of these factors means that s-SNOM is a powerful tool for gaining information complementary to conventional optical and microscopy techniques.