Atomic Force Microscopy (AFM) in Neuroscience

Atomic Force Microscope (AFM) is an important tool for studying biological samples, it can image the surface under liquid. This technology outlines the surface profile by controlling the collection of forces acting between the tiny probe and the surface. It can study the surface structure with a very high signal-to-noise ratio at sub-nanometer resolution and is suitable for a large temperature range and almost all environments. As both an imaging technique and a mechanical tool, AFM provides an excellent opportunity to study soft biological samples such as living brain tissue.

Imaging Methods and Techniques of Neuroscience

AFM works by physically interacting with the cantilever tip and cell surface molecules. The adhesion force between the tip molecule and the cell surface molecule is detected as cantilever deflection, therefore, the cantilever tip can be used to image living cells with atomic resolution and detect single-molecule events in living cells under physiological conditions. This is the only technology that can directly provide structural, mechanical, and functional information with high resolution, allowing biological samples (from single molecules to living cells) to be visualized and manipulated.

Fig.1 Various AFM modes. (Dufrêne, 2017)

Many AFM imaging modes have been developed. These modes can be easily applied to biological systems in principle, thereby further expanding the various information that can be quantified and structurally mapped when imaging complex biological systems. These methods include high-resolution imaging of natural biological structures, simultaneous mapping of mechanical, kinetic, and thermodynamic properties, functional groups and binding sites, free energy landscapes of free radicals and receptor bonds, and electrostatic properties from charge distribution to ion flow.

Application of AFM Technology in Brain Tissue Mechanics

AFM is used in neurobiology, focused on the biomechanics of neurons and glial cells. As the central nervous system (CNS) of the whole body, brain tissue mainly contains neurons and glial cells, which interact with neurotransmitters through electroacoustic and ion signals. AFM non-invasive study of brain morphology and cell mechanics can better understand the development of various diseases, such as neurodegenerative diseases and brain tumors.

• The use of AFM in neuronal biomechanics
• AFM imaging of neurons growing on laminin micrographs shows the role of laminin-guided cell neutral growth and action in growth cone dynamics.
• AFM combined with confocal fluorescence microscopy is used to analyze the morphology of the growth cones of multi-headed nodular neurons in rats.
• 3D AFM imaging of neurons and glial cells provides a lot of information about the 3D structure of cells.
• Prove the elastic properties of different areas of the brain and the fine details of the biomolecular structure

AFM measurement of rat brain hippocampus and cortical regions shows that the mechanical heterogeneity of the subregions and age-dependent tissue stiffness are related, and the brain tissue stiffness of Alzheimer's mice was reduced. These potential applications of AFM in brain development and the characteristics of diseased tissues help to better understand the impact of mechanical induction at the subtissue level.

Fig.2 Sensory neuron optical image (a) and AFM imaging (b, c). (Khalisov, 2017)

A multi-modal, multi-parameter, multi-frequency, high-speed AFM imaging platform will help to understand the dynamics, structure, chemistry, and functional heterogeneity of complex biological systems more comprehensively. The latest advances in AFM make it an ideal tool to understand the role of mechanical cues in brain tissue and to correlate these cues with histopathological features. With the advancement of brain tissue sample preparation methods, coupled with the multi-modalization of AFM bioimaging technology, the use of AFM to diagnose and analyze neurodegenerative diseases covers a wide range of neuroscience networks.

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References

1. Dufrêne, Y.F.; et al. Imaging modes of atomic force microscopy for application in molecular and cell biology. Nature nanotechnology. 2017, 12(4): 295-307.
2. Khalisov, M.M.; et al. Characteristics of receptor-and transducer-coupled activation of the intracellular signaling in sensory neuron revealed by atomic force microscopy. Technical Physics Letters. 2017, 43(1): 85-87.