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revised on 13.10.2020 and posted on 14.10.2020by Haomin Wang, Joseph M. González-Fialkowski, Wenqian Li, Qing Xie, Yan Yu, Xiaoji Xu
Atomic force microscopy-infrared microscopy
(AFM-IR) provides a route to bypass Abbe’s diffraction limit through photothermal
detections of infrared absorption. With the combination of total internal
reflection, AFM-IR can operate in the aqueous phase. However, AFM-IR in contact
mode suffers from surface damage from the lateral shear force between the tip
and sample, and can only achieve 20~25-nm spatial resolution. Here, we develop
the liquid-phase peak force infrared (LiPFIR) microscopy that avoids the
detrimental shear force and delivers an 8-nm spatial resolution. The
non-destructiveness of the LiPFIR microscopy enables in situ chemical
measurement of heterogeneous materials and investigations on a range of
chemical and physical transformations, including polymer surface
reorganization, hydrogen-deuterium isotope exchange, and ethanol-induced
denaturation of proteins. We also perform LiPFIR imaging of the budding site of
yeast cell wall in the fluid as a demonstration of biological applications. LiPFIR
unleashes the potential of in liquid AFM-IR for chemical nanoscopy.