nano-FTIR is an emerging new optical super resolution microscopy technique that enables IR spectroscopy and chemical mapping with 20nm spatial resolution. nano-FTIR employs an externally IR-illuminated sharp metallic AFM tip to create a nanoscale hot-spot at its apex. The optical tip-sample near-field interaction is determined by the local dielectric properties (refractive index) of the sample. Detection of the elastically tip-scattered light simultaneous to AFM imaging yields nanoscale resolved near-field images. Utilizing broadband laser sources like a mid-IR supercontinuum laser for tip illumination and interferometric light detection analogous to classical FTIR spectroscopy, enables near-field spectroscopic measurements with nanometer scale spatial resolution. Recently, nanoscale chemical characterization of mulitcomponent thins film polymer blends and probing of secondary structure in individual protein fibrils have been succesfully demonstrated. Here we demonstrate for the first time nano-FTIR spectroscopy and nanoscaled resolved infrared mapping of a thin crystalline nanocellulose (CNC) film and individual fibers. nano-FTIR spectra are reproducible and are in good agreement with conventional FTIR spectra from similar materials. Remarkably, the nano-FTIR reveal distinct difference between single fiber spectra and the film spectra. The ratio between the group of bands in the 1100-1150 cm-1 spectral range (C-O-C, C-C backbone) and the group of 1300-1400 cm-1 bands is about 3 times larger for the film spectra compared to the fiber spectra. This observation can be explained in terms of the intrinsic polarization selectivity and thus molecular orientation sensitivity of nano-FTIR.

Nano-FTIR spectroscopy: Nanoscale resolved infrared spectroscopy of individual CNC fibers and thin films

255th National Meeting (2018)

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