KANAZAWA, Japan March 19, 2021 / PRNewswire / – Kanazawa University report in Review of Scientific Instruments a recently developed report Atomic Force Microscopy Approach to Imaging Samples and Biological Processes. The method offers higher frame rates and less sample disturbance.
High speed atomic force microscopy (HS-AFM) is an imaging technique that can be used to visualize biological processes, for example protein activity. Today, typical HS-AFM frame rates are as high as 12 frames per second. However, to improve the capabilities of the method so that it can be applied to an increasing range of biological samples, better video speeds are needed. In addition, faster recording times mean less interaction between the sample and the probe, a tip that scans the surface of the sample, making the imaging procedure less invasive. Now, Shingo Fukuda and Toshio Ando from the Nano Life Science Institute (WPI-NanoLSI) at Kanazawa University have developed an alternative HS-AFM approach to increase the frame rate up to 30 frames per second.
An AFM image is generated by laterally moving a tip just above the surface of a sample. During this xy scanning movement, the position of the tip in the direction perpendicular to the xy plane (the z coordinate) will follow the height profile of the sample. The variation of the z-coordinate of the tip produces a height map: the sample image.
Fukuda and Ando worked at HS-AFM in the so-called amplitude modulation mode. The tip is then made to oscillate with a set amplitude. While scanning a surface, the amplitude of oscillation will change due to variations in height in the structure of the sample. To return to the original amplitude, a correction to the tip-sample distance is necessary. The size of the correction is related to the topology of the sample surface and is dictated by the so-called configuration feedback control error. The scientists noted that the feedback control error is different when the tip moves in opposite directions, which is called tracking and kicking. This difference is ultimately due to the different physical forces at play when the tip is 'pulled' (traced) and when the tip is 'pushed' (back).
Drawing on their knowledge of the physics of track and trace, Fukuda and Ando developed an imaging regimen that avoids tracking. This must be properly taken into account in the control algorithm. The researchers tested their single-trace imaging mode on actin filament samples. (Actin is a very common protein in cells.) The images were not only faster, but also less invasive: the filaments broke much less frequently. They also recorded polymerization processes (through protein-protein interactions); again, the method was found to be faster and less disruptive compared to the standard AFM scan and trace operation.
The scientists are confident that their "simple and highly efficient method will soon be installed in existing and future HS-AFM systems, and will enhance a wide range of HS-AFM imaging studies in biophysics and other fields."
Legend from Figure 1: Difference in invasiveness between trace and trace processes.
(a) Raster scan: trace scan (red line) and back scan (blue line) of the sample stage,
(b) scan directions of the tip relative to the sample at the traceback and scan processes,
(c) difference in feedback control error between traceback and traceback processes. Actin filament error images oriented almost along the Y axis (top) and the error profile (bottom),
(d, e) difference in the directions of the torques produced by the lateral and vertical forces exerted on the cantilever from the sample during the trace (d) and recoil (e) scanning processes,
(f, g) HS-AFM images of actin filaments captured at 10 fps in OTI (f) and ORI (g) modes. In ORI mode, actin filaments broke rapidly.
Figure 2. The circuit installed for OTI mode and its operation.
(a) During back scan, a DC shift signal ( A or <0) is added to the amplitude signal ( A ). The feedback control works as if the probe is in strong contact with the sample and therefore the sample stage moves away from the tip.
(b) Trigger signal for X scanner in OTI mode (top), DC offset signal added to true amplitude signal (center) and Z scanner offset (bottom).
Shingo Fukuda and Toshio Ando . Faster High Speed Atomic Force Microscopy for Imaging Biomolecular Processes, Rev. Sci. Instrum. 92 033705 (2021).
DOI: 10.1063 / 5.0032948
About WPI nanoLSI Kanazawa University
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WPI Nano Life Science Institute (WPI-NanoLSI)
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About the Nano Life Science Institute (WPI-NanoLSI)
Nano Life Science Institute (NanoLSI) at Kanazawa University is a research center established in 2017 as part of the Initiative of the World Premier International Research Center of the Ministry of Education, Culture, Sports, Science and Technology. The objective of this initiative is to form world-class research centers. NanoLSI combines the most advanced knowledge of bio-scanning probe microscopy to establish 'nanoendoscopic techniques' to directly image, analyze and manipulate biomolecules to understand the mechanisms that govern life phenomena such as disease.
About Kanazawa University
As the leading comprehensive university on the Sea coast of Japan Kanazawa University has contributed greatly to higher education and academic research in Japan since its founding in 1949. three colleges and 17 schools offering courses in subjects including medicine, computer engineering and humanities.
The University is located on the coast of the Sea of Japan in Kanazawa – a city rich in history and culture. The city of Kanazawa has a highly respected intellectual profile since the fiefdom (1598-1867). Kanazawa University is divided into two main campuses: Kakuma and Takaramachi for its approximately 10,200 students, including 600 from abroad.
SOURCE Kanazawa University