Infrared spectroscopy gets down to nanoscale

"Until now, nanotechnology could only barely benefit from this powerful technique, because diffraction limits conventional infrared spectroscopic microscopy to a resolution of at least a few micrometres," Markus Brehm of the Max Planck Institute told nanotechweb.org. "With our approach we overcome the diffraction limit and bring the full power of infrared spectroscopy to the nanoscale." Brehm and colleagues used platinum covered cantilevered silicon tips to map samples with s-SNOM for topography, infrared amplitude and phase contrast. They looked at spherical beads of poly(methyl methacrylate) (PMMA) with diameters of 30–70&nbasp;nm and cylindrical tobacco mosaic viruses that were 18 nm in diameter. "Infrared spectroscopy works surprisingly well," said Brehm. "Tiny amounts of material (10-20 litre) provide a remarkably strong contrast – the required sample volume is orders of magnitude smaller than with conventional far-field infrared microscopy." The virus and PMMA each had a different infrared spectral fingerprint, which enabled s-SNOM to distinguish between them. The technique could provide label-free chemical analysis: it was not affected by the dimensions of the probed objects or the changing environment of the nanoparticles. "In our opinion, the technique will be useful whenever chemical identification of material is needed at nanoscale resolution," said Brehm. "This could be the case for the characterization of engineered devices such as nano-electronic conductive structures, as well as for biological specimens such as protein complexes and cell substructures. Even if high spatial resolution is not required, the sensitivity enhancement that comes with our microscope will allow chemical identification in cases where only a tiny amount of sample material is available." According to the researchers, infrared spectroscopy can also provide structural identification such as the secondary structure of a protein. The s-SNOM technique could perhaps supply the information at the single protein or even protein-subunit level. Structural data of this type could help scientists understand Alzheimer's disease and bovine spongiform encephalopathy. The technique's near-field contrast depended on the infrared frequency. As a result, the researchers took a number of images of their samples, each using a different frequency. "The experiment required numerous, repeated scanning of the same sample but with different wavelengths," said Brehm. "For example, one spectrum was extracted from 59 images taken in 3 days work. It was necessary to maintain exactly the same conditions for each, especially atomic force microscope imaging conditions, interferometer stability, and beam alignment." Now the researchers hope to make their infrared-spectroscopic near-field microscopy technique faster, easier and more reliable. "The key is to move from our sequential way of taking spectra – taking images repeatedly at different wavelengths - to a parallel method that takes a complete spectrum at each pixel during scanning," said Brehm. "We have, in fact, just verified this aim in a system that combines infrared frequency-comb spectroscopy with near-field microscopy." "Source":[ http://nanotechweb.org/articles/news/5/6/8/1]

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