In Liquid Infrared Scattering Scanning Near-Field Optical Microscopy for Chemical and Biological Nanoimaging

• DOI: 10.1021/acs.nanolett.0c01291
• Publication Date: 2020-05-01T19:05:10Z
• Authors: 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; A. Scott Lea
• Keywords: ELECTRON-MICROSCOPY; SPECTROSCOPY; Spectrophotometry, Infrared; in situ; NANOSPECTROSCOPY; 535; 02 engineering and technology; DIFFRACTION; Microscopy, Atomic Force; Vibration; SPECIMENS; MOLECULES; Nanoparticles; Nanotechnology; bioimaging; 0210 nano-technology; in-liquid

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.