Review: Advanced Atomic Force Microscopy Modes for Biomedical Research

Abstract

Visualization of biomedical samples in their native environments at the microscopic scale is crucial for studying fundamental principles and discovering biomedical systems with complex interaction. The study of dynamic biological processes requires a microscope system with multiple modalities, high spatial/temporal resolution, large imaging ranges, versatile imaging environments and ideally in-situ manipulation capabilities. Recent development of new Atomic Force Microscopy (AFM) capabilities has made it such a powerful tool for biological and biomedical research. This review introduces novel AFM functionalities including high-speed imaging for dynamic process visualization, mechanobiology with force spectroscopy, molecular species characterization, and AFM nano-manipulation. These capabilities enable many new possibilities for novel scientific research and allow scientists to observe and explore processes at the nanoscale like never before. Selected application examples from recent studies are provided to demonstrate the effectiveness of these AFM techniques.

Keywords: atomic force microscopy; biomedical research; high-speed imaging; material property mapping; mechanobiology; nano-manipulation; nanotechnology.

Figure 1

Typical size of biological objects and resolution capabilities of microscopy techniques.

Figure 2

Principle illustration of a conventional AFM including a cantilever probe with optical beam deflection sensor and piezo-acoustic resonance excitation, a nanopositioning system, and an imaging motion controller.

Figure 3

Advanced imaging capability illustration: (a) high-speed imaging to track virus movement on cells, (b) mechanobiology with viscoelastic property mapping and single-cell force spectroscopy, (c) chemical species characterization using near-field optics with AFM, and (d) AFM biomedical sample manipulation for fluid extraction from a cell.

Figure 4

HSAFM images of skeletal HMM chemomechanical cycle: the frames show a double-headed myosin fragment bound to F-actin at different states in 2 µM ATP with the red dot indicating the center of mass. Image created at 6.7 frames per second with a 30 nm scale bar. (PPS: pre-power-stroke, post-PS: post-power-stroke) (adapted from [21] with permission, copyright 2021 American Chemical Society).

Figure 5

Mechanical property mapping of a native cytoplasmic purple membrane adsorbed on mica and imaged in a buffer solution with topography, Young’s modulus, deformation, and adhesion (adapted from [72] with permission, copyright 2013 Springer Nature).

Figure 6

Scattering type SNOM image of collagen fibrils on a nerve section surface: (a,b) topography image of a section of the collagen fibrils, (c) third harmonic amplitude image at 1100 cm${}^{-1}$ with labels of the high-density area, (d) force phase image of the collagen fibrils (adapted with permission from [91], copyright 2021 Springer Nature).

Figure 7

FluidFM principle illustration: (a) schematic diagram of a hollow cantilever with microfluidic channels, (b,c) SEM image of a FluidFM probe tip with openings on the tip apex for cell manipulation and near the tip apex for particle injection and sampling, and (d) schematic of an injection process of particles into cells after penetrating the membrane (adapted with permission from [121], copyright 2009 American Chemical Society).