Biomolecular systems with faster and less-invasive atomic force microscopy by Kanazawa University

Researchers at Kanazawa University report in Review of Scientific Instruments a newly developed atomic force microscopy approach for imaging biological samples and processes. the tactic offers higher frame rates and fewer disturbance of samples.

High-speed atomic force microscopy (HS-AFM) is an imaging technique which will be used for visualizing biological processes, for instance the activity of proteins. Nowadays, typical HS-AFM frame rates are as high as 12 frames per second. so as to enhance the capabilities of the tactic , in order that it are often applied to an ever expanding range of biological samples, better video rates are needed, though.

Moreover, faster recording times imply less interaction between the sample and therefore the probe — a tip scanning the sample’s surface — making the imaging procedure less invasive. Now, Shingo Fukuda and Toshio Ando from Nano bioscience Institute (WPI-NanoLSI), Kanazawa University have developed an alternate HS-AFM approach to extend the frame rate up to 30 frames per second.

An AFM image is generated by laterally moving a tip around just above a sample’s surface. During this xy-scanning motion, the tip’s position within the direction perpendicular to the xy-plane (the z-coordinate) will follow the sample’s height profile. The variation of the z-coordinate of the tip then produces a height map — the image of the sample.

Fukuda and Ando worked on HS-AFM within the so-called amplitude-modulation mode. The tip is then made to oscillate with a group amplitude. While scanning a surface, the oscillation amplitude will change due to height variations within the sample’s structure. to urge back to the first amplitude, a correction to the tip-sample distance must be made. How large the correction must be is said to the sample’s surface topology, and is dictated by the so-called feedback control error of the setup.

The scientists noted that the feedback control error is different when the tip moves in opposite directions, called tracing and retracing. This difference is ultimately thanks to the various physical forces at play when the tip is ‘pulled’ (tracing) and when it’s ‘pushed’ (retracing).

Based on their insights into the physics of the tracing and retracing processes, Fukuda and Ando developed an imaging regime that bypasses retracing. This then must be properly accounted for within the controlling algorithm. The researchers tested their only-trace-imaging mode on actin filament samples. (Actin may be a protein quite common in cells.) The imaging wasn’t only faster, but also less invasive — the filaments broke much less frequently. They also recorded polymerization processes (through protein–protein interactions); again, the tactic was found to be faster and fewer disturbing compared to the quality AFM tracing-retracing operation.

The scientists are confident that their “simple and highly effective method will soon be installed within the existing and upcoming HS-AFM systems, and can improve a good range of HS-AFM imaging studies in biophysics and other fields.”

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