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Nanoscale Fourier Transform Infrared Spectroscopy

Nanoscale Fourier transform infrared spectroscopy (nano-FTIR) is a high-resolution chemical imaging system, which combines the nanoscale spatial resolution of atomic force microscopy with the chemical sensitivity of infrared spectroscopy. This resource is used to identify and characterize different chemical and biological materials. Also known as scattering-type near-field optical microscopy (s-SNOM), the nano-FTIR instrument was developed through a partnership with Professor Markus Raschke at the University of Colorado Boulder and is designed to provide spectroscopic infrared vibrational nanoimaging at ultrahigh spatial resolution down to 10 nm. Nano-FTIR can be used to analyze a variety of samples, from proteins to minerals, and, thus, can advance EMSL’s mission through its application to both biological and environmental processes.

Nano-FTIR provides vibrational spectral information in the 800 to 4500 cm-1 (13 to 2 µm) range, sensitivity down to the molecular level, and can be used to create maps of chemical composition and structure of a variety of biological and chemical samples such as minerals and biostructures. The system uses tunable infrared light that can be focused onto a gold-coated atomic force microscopy tip with a peak power of > 1mW, enabling a tip-enhanced field at the apex of the probe. Spatial resolution of the instrument is dictated by the geometry of the tip and has been shown to be less than 10 nm. For s-SNOM imaging, the atomic force microscopy is operated in dynamic non-contact mode. The tip-scattered radiation is detected in the backscattering direction and the near-field signal is extracted from the far-field background by lock-in detection of the synchronized signal component with the tip dither frequency to provide contrast due to the nonlinear distance dependence of the optical tip-sample coupling.

photo of a metal instrument encased in glass
Nanoscale Fourier transform infrared spectroscopy (nano-FTIR) supports the Structural Biology and Biogeochemical Transformations Integrated Research Platforms.

Research application

Supporting the Structural Biology Integrated Research Platform, nano-FTIR can characterize proteins and their associated secondary structure, as well as map other biostructures. The instrument allows for in situ nano imaging of chemical and biological systems using in-liquid operation through a novel bottom illumination geometry.

Supporting the Biogeochemical Transformations Integrated Research Platform, nano-FTIR tracks chemical changes in biogeochemical or hydrological systems.

Supporting the Terrestrial-Atmospheric Processes Integrated Research Platfom, nano-FTIR chemically identifies nanoscale aerosol particles. 

Tips for success

  • Samples must be compatible with atomic force microscopy. This requires a flat surface of < 500 nm roughness across a 10-micron region of interest.

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