Evanescent-field-induced Raman scattering for bio-friendly fingerprinting at sub-cellular dimension.

Evanescent field induced chemical imaging concept has been realized in analytical platform based on the µ-tip-enhanced Raman scattering spectroscopy (µ-TERS). The technique aimed to minimize thermal decomposition of dried biological sample as the result of huge concentration of optical field near the tip by increasing the size of an aperture-less "excitation source". µ-TERS technique is similar to classical biosensor systems based on propagating surface plasmon resonance phenomenon but with sensitive elements a few micrometers in size that can be targeted to the area of interest. The utility of the concept is exemplified by the analysis of dried single cell envelope of genetically modified Saccharomyces cerevisiae yeast cells, which do not have any heat-removing pathways, by water as in the case of the living cell. Practical excitation conditions effective for µ-TERS Raman observation of single layer dried biological samples without photodamage-related spectral distortion have been determined - the allowable limit is above 30s at 13 µW/µm(2). Finally, potential of µ-TERS spectroscopy as new bio-friendly instrumental platform for chemical fingerprinting and analytical characterization of buried nanoscale features is discussed.