In Liquid Infrared Scattering Scanning Near-Field Optical Microscopy for Chemical and Biological Nanoimaging
Brian O'callahan, Kyoung‐Duck Park, Irina Novikova, Tengyue Jian, Chun‐Long Chen, Eric A. Muller, Patrick Z. El‐Khoury, Markus B. Raschke, Scott Lea
Abstract
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.