In Liquid Infrared Scattering Scanning Near-Field Optical Microscopy for Chemical and Biological Nanoimaging
Reviews and Highlights | Quantum Science | Molecular and Soft-matter | Ultrafast Nano-optics and Nanophotonics | Mineralogy and Geochemistry |
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Brian T. O Callahan, Kyoung-Duck Park, Irina V. Novikova, Tengyue Jian, Chun-Long Chen, Eric A. Muller, Patrick Z. El-Khoury, Markus B. Raschke, and A. Scott Lea
Nano Lett. 20, 4497 (2020).
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Imaging biological systems with simultaneous intrinsic chemical specificity and nanometer spatial resolution in their typical native liquid environment has remained a long-standing challenge. Here, we demonstrate a general approach of chemical nanoimaging in liquid based on infrared scattering scanning near-field optical microscopy (IR s-SNOM). It is enabled by combining AFM operation in a fluid cell with evanescent IR illumination via total internal reflection, which provides spatially confined excitation for minimized IR water absorption, reduced far-field background, and enhanced directional signal emission and sensitivity. We demonstrate in-liquid IR s-SNOM vibrational nanoimaging and conformational identification of catalase nanocrystals and spatio-spectral analysis of biomimetic peptoid sheets with monolayer sensitivity and chemical specificity at the few zeptomole level. This work establishes the principles of in-liquid and in situ IR s-SNOM spectroscopic chemical nanoimaging and its general applicability to biomolecular, cellular, catalytic, electrochemical, or other interfaces and nanosystems in liquids or solutions.