Istruzione e Formazione
Kanazawa University research: Speeding up atomic force microscopy
The basic idea of AFM is to make a very small tip scan the surface of a sample. During this horizontal ('xy') scan, the tip, which is attached to a small cantilever, follows the sample's vertical ('z') profile, inducing a force on the cantilever that can be measured. The magnitude of the force at the 'xy' position can be related to the 'z' value; the 'xyz' data generated during a scan then result in a height map providing structural information about the investigated sample. In HS-AFM, the working principle is slightly more involved: the cantilever is made to oscillate near its resonance frequency. When the tip is moved around a surface, the variations in the amplitude of the cantilever's oscillation — resulting from the tip's interaction with the sample's surface — are recorded, as these provide a measure for the local 'z' value. Amplitude variation detectors have an intrinsic slowness, called latency, as a finite time interval is normally required to detect a change in amplitude. Amplitude detector latency is one of the main bottlenecks towards improving the speed of HS-AFM.
Umeda and colleagues invented a cleverly designed amplitude detector that has zero intrinsic latency. The detector is based on the trigonometric calculation, in which the calculation of = (sin ω + cos ω ) = ( sinω ) + ( cosω ) is performed using an incoming sin wave sinω . The key step for the fast detection was to obtain the cosine wave cosω by the differential operation. Hence, the electronic circuit invented here was named DB (differential based) amplitude detector. The scientists built a test circuit with this architecture, and evaluated its speed performance in the range of 300 – 1500 kHz carrier frequency. The DB amplitude detector resulted in about 10 times faster characteristics than the schemes typically used until now.
The researchers also tested the DB amplitude detector in a real HS-AFM experiment. They successfully recorded actin filaments, one of the cytoskeletal filaments found in eukaryotic cells, with a scanning velocity of 800 micrometers per second, which is four times faster than with a typical setup. The higher recording speeds not only results in a higher video frame rate (50 milliseconds per frame) but it also has the advantage of being less invasive — in the standard setup, the filament collapsed after 1 second, whereas with the new detector, the biomolecule was stably observed for 30 seconds.
The detector of Umeda and colleagues promises better performance in terms of imaging speed and less-invasiveness compared to conventional detectors. Quoting the scientists: "By overcoming the obstacle of the amplitude detector bandwidth, we have opened the road to increasing the temporal resolution of HS-AFM."
Kenichi Umeda , Chihiro Okamoto , Masahiro Shimizu , Shinji Watanabe , Toshio Ando , Noriyuki Kodera . Architecture of zero-latency ultrafast amplitude detector for high-speed atomic force microscopy, , 181602 (2021)
URL: https://aip.scitation.org/doi/10.1063/5.0067224
DOI: 10.1063/5.0067224
https://nanolsi.kanazawa-u.ac.jp/wp-content/uploads/2021/11/fig1_uk_kn.png
Figure 1. Diagram of ampitude detection based on the trigonometric calculation. To obtain amplitude from an incoming sin wave sinω , after the calculation of = (sin ω + cos ω ) = ( sinω ) + ( cosω ) is performed, the square root operation is subsequently performed. So far, a phase-shift-based (PSB) operation that has finite intrinsic latency has been used to calculate cosω (blue box shown in the center). Here, the scientists use a differential-based (DB) operation that has zero intrinsic latency to calculate cosω (red box shown in the bottom center). Furthermore, it was found that a faster amplitude detection and less invasive imaging were achieved by skipping the square root operation.
Hiroe Yoneda
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WPI Nano Life Science Institute (WPI-NanoLSI)
Kanazawa University
Kakuma-machi, Kanazawa 920-1192, Japan
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Nano Life Science Institute (NanoLSI), Kanazawa University is a research center established in 2017 as part of the World Premier International Research Center Initiative of the Ministry of Education, Culture, Sports, Science and Technology. The objective of this initiative is to form world-tier research centers. NanoLSI combines the foremost knowledge of bio-scanning probe microscopy to establish 'nano-endoscopic techniques' to directly image, analyze, and manipulate biomolecules for insights into mechanisms governing life phenomena such as diseases.
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As the leading comprehensive university on the Sea of Japan coast, Kanazawa University has contributed greatly to higher education and academic research in Japan since it was founded in 1949. The University has three colleges and 17 schools offering courses in subjects that include 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 time of the fiefdom (1598-1867). Kanazawa University is divided into two main campuses: Kakuma and Takaramachi for its approximately 10,200 students including 600 from overseas.