Separate-scan atomic force microscope for fast infrared scattering-type scanning near-field optical microscope

TL;DR

This paper introduces a combined high-speed AFM and infrared sSNOM system enabling rapid nanoscale chemical imaging of biomolecules in aqueous environments, overcoming previous speed limitations.

Contribution

It presents a novel separate-scan AFM integrated with BI-sSNOM, achieving high-speed imaging suitable for observing dynamic biological processes.

Findings

Achieved a Z-axis bandwidth of ~70 kHz and XY-axis of ~6 kHz in AFM scanner.

Successfully imaged actin filaments with the AFM.

Validated sSNOM imaging on purple membranes and microtubules.

Abstract

Pseudo-heterodyne scattering-type scanning near-field optical microscopy (sSNOM) is applied in the mid-infrared region to detect the chemical composition of biomolecules on the nanoscale. However, the application of sSNOM in molecular biology has been limited to static images in air. Recently, bottom illumination sSNOM (BI-sSNOM) was developed for operation in water. Yet, the scan rate of sSNOM remains a bottleneck to record protein structural changes in aqueous solution on the seconds time scale. We designed an optical and mechanical system consisting of a separate scan high-speed atomic force microscope (HS-AFM) coupled to the BI-sSNOM optics. The designed AFM scanner has a mechanical bandwidth of ca 70 kHz along the Z-axis, and ca 6 kHz along the XY-axis, equivalent to the sample scanning HS-AFM. The AFM performance is demonstrated by imaging actin filaments. The optical design is validated by sSNOM experiments on purple membranes and microtubules.