Dual-Color Peak Force Infrared Microscopy

Abstract

Peak force infrared (PFIR) microscopy achieves nanoscale infrared imaging at sub-10 nm spatial resolution through photothermal mechanical detection of atomic force microscopy (AFM). However, it suffers from a major limitation that only one infrared frequency can be scanned for an AFM frame at a time. To overcome this limitation, we report here dual-color PFIR microscopy that enables simultaneous imaging at two infrared frequencies. This dual-color PFIR microscopy bypasses the limitations of frame drift and distortion of AFM when comparing two images of different infrared frequencies. We benchmark the performance and spatial resolution of this method using structured polymers exhibiting phase separation. We further demonstrate the application of this technique in imaging biological samples by mapping the cell wall of Escherichia coli (E. coli) bacteria. The presence of a bacterial outer membrane was detected without extrinsic labels. This dual-color PFIR microscopy enables simultaneous nondestructive chemical nanoimaging of multiple chemical components and will be useful for potential applications such as in situ dual-channel monitoring of chemical reactions.

Lock-in amplifier based peak force infrared microscopy

“…In lock-in based PFIR microscopy, such an increase in noise contribution is inevitable, imposing a trade-off between performance and instrumental complexity. In addition, the recently developed dual-color PFIR microscopy, 24 allows two PFIR images to be collected simultaneously without relative drift. In the case of lock-in amplifier based PFIR microscopy, utilization of multiple IR sources is not straightforward, if possible, at all.…”

Dual-Frequency Peak Force Photothermal Microscopy for Simultaneously Spatial Mapping Chemical Distributions and Energy Dissipation

“…Such photothermal expansions are detected by the deflections and oscillations of the AFM probe. , Through analysis of the mechanical responses from the AFM cantilever, the magnitude of the infrared or visible absorption can be extracted. In our experimental implementation, we adopted the simultaneous detection configuration of the dual-color PFIR microscopy to incorporate both the infrared excitation and the visible excitations. The AFM-based photothermal imaging of both infrared and visible frequencies is done simultaneously in one AFM frame scan.…”

Toward the Next Frontiers of Vibrational Bioimaging

“…The development of broadband and multiplexed SRS and CARS methods has increased imaging speed and expanded the volume of obtainable vibrational information. For the point-scan MIP and force-detected AFM+IR, hyperspectral data can be constructed sequentially using multiple laser lines in parallel , or a fast-tunable QCL. On the other hand, implementations of broadband MIP and force-detected AFM+IR are of increasing interest.…”