Atomic Force Microscopy Imaging of Food Polysaccharides

Abstract

Atomic force microscopy (AFM) is a type of scanning probe microscopy that generates images (primarily topographical ones) by scanning the surface of samples with a sharp tip. AFM is applicable to samples with low electric conductivities, and its operating range spans that accessible to both light and electron microscopes, allowing for molecular resolution. These features of AFM enable soft materials to be visualized under natural conditions without harsh or damaging procedures. For food polysaccharides, AFM is capable of visualizing not only dispersed molecules but also molecular assemblies with an advantage over other physical techniques in quantifying the heterogeneity of samples. From these perspectives, AFM is one of the most versatile techniques for obtaining structural information on food polysaccharides, contributing to the progress of this research area. In this article, AFM images of various food polysaccharides are presented along with the usefulness and limitations of this microscopy technique.Keywords: atomic force microscopy (AFM), food polysaccharides, dispersed molecule, molecular assembly, supermolecular structure *To whom correspondence should be addressed. E-mail: tfunami@saneigenffi.co.jp IntroductionAtomic force microscopy (AFM), developed by Binning and Quate in 1986, is a type of scanning probe microscopy that generates images, primarily topographical ones, by scanning the surface of samples with a sharp tip attached to a cantilever. This means that AFM generates images by touching samples rather than observing them. AFM is applicable to samples with low electric conductivities, differing from a scanning tunneling microscope, and is free from a diffraction limit, allowing for a molecular resolution up to the sub-nanometer level. These features of AFM enable the visualization of soft materials, including biomaterials and food materials under natural conditions without harsh or damaging preparative and imaging procedures used in conventional electron microscopy methods, including dyeing, drying, and metal deposition. AFM imaging works both in air and aqueous environments, making it possible to visualize samples in a hydrated form such that the samples exhibit behaviors similar to those seen in real systems.As a tool for the study of food hydrocolloids, AFM is capable of visualizing not only dispersed or isolated molecules

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