FM-AFM imaging

Figure 18.5 shows FM-AFM images of purple membranes. In these images, individual bR molecules constituting the membrane are clearly resolved (Fig. 18.5b). 

Figure 18.5 FM-AFM images of a purple membrane including bR protein molecules adsorbed on muscovite mica in phosphate buffer solution, (a] Scale bar 60 nm. (b) Scale bar 16 nm. (c, d] Scale bars 1.4 nm. (c] and (d) are the magnified images of the areas indicated by the white squares in Cb).2i...

The author and coworkers obtained the first subnanometer-resolution FM-AFM image of biological molecules by imaging a lipid bilayer consisting of dipalmitoylphosphatidylcholine (DPPC) molecules (Fig. 18.6a). 

Figure 18.6 (a] Model of a DPPC molecule, (b) model of a DPPC bilayer formed on mica In water, and (c) FM-AFM image of a DPPC bilayer in water [15 nm X 7.5 nm]. ... 

FM-AFM imaging of biological molecules is possible even with a stiff cantilever. 

Figure 18.7 FM-AFM images of lAPP fibrils on mica in PBS solution, (a) 800 nm x 800 nm, A/ = —55 Hz, tip velocity = 1 p,m/s. (b) 10 nm x 10 nm, A/ = +50 Hz, tip velocity = 195 nm/s. (c) Schematic model of the /i-strands. Abbreviations-. lAPP, islet amyloid polypeptide PBS, phosphate buffer solution.

Figure 18.7a,b shows FM-AFM images of amyloid fibrils formed from the lAPP deposited on mica in PBS solution. lAPP fibrils are associated with type 2 diabetes when deposited in pancreatic islets. The image shows finely striped features perpendicular to the fibril axis. The distance between adjacent stripes is approximately 0.5 nm. A previous X-ray diffraction study suggested the existence of periodic structure along lAPP fibril axes with a spacing of 0.47 nm. 

Figure 18.9 (a] Schematic model of the lipid-ion complex formed at the lipid-water interface, (b] and (c) Sequential FM-AFM Images of the same area of the DPPC bllayer in PBS solution. Height range 0.1 nm. Tip velocity 120 nm/s. Imaging speed 85 s/image. ... 

Figure 18.9b,c shows sequential FM-AFM images taken on a DPPC bilayer in PBS. ... 

The author and coworkers applied FM-AFM to the investigation of the DPPC-cholesterol (50-50 mol%) mixed bilayer. Figure 18.10 shows an FM-AFM image of a DPPC-cholesterol mixed bilayer formed on mica in PBS. 

In addition to the structure of the molecular surfaces, the distribution of water " and ions interacting with the surface is also visualized by FM-AFM. Finally, the molecular-scale arrangement of the unknown biomolecular complex (i.e., the lipid-cholesterol complex) was determined by FM-AFM imaging. 

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