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| 1.
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Ogata, Shoichiro ; Kobayashi, Naritaka ; Kitagawa, Takuya ; Shima, Shohei ; Fukunaga, Akira ; Takatoh, Chikako ; Fukuma, Takeshi
概要:
In this study, nanoscale corrosion behavior of copper fine wires in dilute NaCl solution is studied by atomic force micr
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oscopy and electron backscatter diffraction. The dissolution rate of grains constituting the wires strongly depends on their crystallographic orientation. In pure water, the dissolution rate increases in the order of (111) < (001) < (110). Addition of Cl- dramatically increases the dissolution rate of the (111) surface to alter the order to (110) ≈ (001) ≈ (111) at 0.1 mM. These results show that the crystallographic orientation dependence is significantly changed by a slight increase of Cl- concentration in dilute solution. © 2016 Elsevier Ltd.<br />Embargo Period 24 months
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| 2.
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Fukuma, Takeshi ; Onishi, K. ; Kobayashi, N. ; Matsuki, A. ; Asakawa, Hitoshi
概要:
In this study, we have investigated the performance of liquid-environment FM-AFM with various cantilevers having differe
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nt dimensions from theoretical and experimental aspects. The results show that reduction of the cantilever dimensions provides improvement in the minimum detectable force as long as the tip height is sufficiently long compared with the width of the cantilever. However, we also found two important issues to be overcome to achieve this theoretically expected performance. The stable photothermal excitation of a small cantilever requires much higher pointing stability of the exciting laser beam than that for a long cantilever. We present a way to satisfy this stringent requirement using a temperature controlled laser diode module and a polarization-maintaining optical fiber. Another issue is associated with the tip. While a small carbon tip formed by electron beam deposition (EBD) is desirable for small cantilevers, we found that an EBD tip is not suitable for atomic-scale applications due to the weak tipsample interaction. Here we show that the tipsample interaction can be greatly enhanced by coating the tip with Si. With these improvements, we demonstrate atomic-resolution imaging of mica in liquid using a small cantilever with a megahertz-order resonance frequency. In addition, we experimentally demonstrate the improvement in the minimum detectable force obtained by the small cantilever in measurements of oscillatory hydration forces. © 2012 IOP Publishing Ltd.
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| 3.
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Iwanaga, Atsushi ; Asakawa, Hitoshi ; Fukuma, Takeshi ; Nakamichi, Momoka ; Shigematsu, Sakurako ; Linder, Markus B. ; Haruyama, Tetsuya
概要:
金沢大学理工研究域バイオＡＦＭ先端研究センター<br />A groundbreaking method for ordered molecular layer preparation on a solid surface employin
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g the drop-stamp method has been developed by us taking advantage of the characteristics of the HFB molecule as a self-organizer/adsorption carrier. It is a smart method which can be used to prepare a self-organized protein layer on a solid surface without unspecific adsorption or defects. In our previous report, we clarified the self-organizing nature of HFB-tagged protein molecules on a surface of a solution droplet. In this report, a protein layer was prepared on a HOPG surface by using the drop-stamp method with a maltose binding protein (MBP)-tagged HFBII molecule. The structure of the stamped protein layer was investigated using frequency modulation atomic force microscopy (FM-AFM) in a liquid condition. The FM-AFM images show that the drop-stamp method can prepare an ordered protein layer on a solid surface smartly. The drop-stamp method using a HFB carrier is a practical method which can be used to prepare an ordered protein layer on a solid substrate surface without unspecific adsorption defects. © 2011 Elsevier B.V.
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| 4.
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Fukuma, Takeshi ; Mostaert, Anika S. ; Serpell, Louise C. ; Jarvis, Suzanne P.
概要:
金沢大学フロンティアサイエンス機構<br />We have investigated the surface structure of islet amyloid polypeptide (IAPP) fibrils and α-synu
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clein protofibrils in liquid by means of frequency modulation atomic force microscopy (FM-AFM). Ångström- resolution FM-AFM imaging of isolated macromolecules in liquid is demonstrated for the first time. Individual β-strands aligned perpendicular to the fibril axis with a spacing of 0.5 nm are resolved in FM-AFM images, which confirms cross-β structure of IAPP fibrils in real space. FM-AFM images also reveal the existence of 4 nm periodic domains along the axis of IAPP fibrils. Stripe features with 0.5 nm spacing are also found in images of α-synuclein protofibrils. However, in contrast to the case for IAPP fibrils, the stripes are oriented 30° from the axis, suggesting the possibility of β-strand alignment in protofibrils different from that in mature fibrils or the regular arrangement of thioflavin T molecules present during the fibril preparation aligned at the surface of the protofibrils. © IOP Publishing Ltd.
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| 5.
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論文
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Fukuma, Takeshi ; Okazaki, Yasutaka ; Kodera, Noriyuki ; Uchihashi, Takayuki ; Ando, Toshio
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金沢大学 理工研究域 数物科学系<br />We have developed the atomic force microscope scanner with the high resonance frequency of 540 kHz
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in the z axis using a piezosupport mechanism "inertia balance support." In the method, a cubic piezoactuator is supported at the four sides perpendicular to the extension axis, by which the resonance frequency of the scanner remains as high as that of the actuator in the free vibration. The scanner allows driving at low voltage ±15 V for the practical z scan range of 330 nm. We demonstrate the applicability of the scanner to the true-atomic-resolution imaging of mica in liquid. © 2008 American Institute of Physics.
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| 6.
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Fukuma, Takeshi ; Okazaki, Yasutaka ; Kodera, Noriyuki ; Uchihashi, Takayuki ; Ando, Toshio
概要:
金沢大学フロンティアサイエンス機構<br />金沢大学理工研究域数物科学系<br />We have developed the atomic force microscope scanner with the high resonance
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frequency of 540 kHz in the z axis using a piezosupport mechanism "inertia balance support." In the method, a cubic piezoactuator is supported at the four sides perpendicular to the extension axis, by which the resonance frequency of the scanner remains as high as that of the actuator in the free vibration. The scanner allows driving at low voltage ±15 V for the practical z scan range of 330 nm. We demonstrate the applicability of the scanner to the true-atomic-resolution imaging of mica in liquid. © 2008 American Institute of Physics.
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| 7.
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論文
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Asakawa, Hitoshi ; Ikegami, Koji ; Setou, Mitsutoshi ; Watanabe, Naoki ; Tsukada, Masaru ; Fukuma, Takeshi
概要:
In this study, we directly imaged subnanometer-scale structures of tubulins by performing frequency modulation atomic fo
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rce microscopy (FM-AFM) in liquid. Individual α-helices at the surface of a tubulin protofilament were imaged as periodic corrugations with a spacing of 0.53 nm, which corresponds to the common pitch of an α-helix backbone (0.54 nm). The identification of individual α-helices allowed us to determine the orientation of the deposited tubulin protofilament. As a result, C-terminal domains of tubulins were identified as protrusions with a height of 0.4 nm from the surface of the tubulin. The imaging mechanism for the observed subnanometer-scale contrasts is discussed in relation to the possible structures of the C-terminal domains. Because the C-terminal domains are chemically modified to regulate the interactions between tubulins and other biomolecules (e.g., motor proteins and microtubule-associated proteins), detailed structural information on individual C-terminal domains is valuable for understanding such regulation mechanisms. The results obtained in this study demonstrate that FM-AFM is capable of visualizing the structural variation of tubulins with subnanometer resolution. This is an important first step toward using FM-AFM to analyze the functions of tubulins. © 2011 Biophysical Society.
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| 8.
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論文
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Kobayashi, Naritaka ; Asakawa, Hitoshi ; Fukuma, Takeshi
概要:
Local potential distribution plays important roles in physical, chemical and biological processes at a solid/liquid inte
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rface. However, the measurement of a local potential distribution in liquid has been a long-standing challenge, which has hindered understanding of the mechanisms for the various interfacial phenomena. Recently, we have developed a method to overcome this problem [Kobayashi, Rev. Sci. Instrum. 81, 123705 (2010)], which is referred to as open-loop electric potential microscopy (OL-EPM). Here, we present its first application to quantitative measurements of local potential distribution in liquid. In OL-EPM, an ac bias voltage is applied between a tip and sample and the first and second harmonic cantilever oscillations induced by the electrostatic force are detected and used for the calculation of a potential value. In the equation for the potential calculation, here we introduce a correction factor to cancel out the error caused by the difference in the deflection sensitivity to the first and second harmonic electrostatic forces. With the improved method, we have performed potential measurements of two types of latex beads with different surface charges. The measured potential difference between the different types of latex beads approximately corresponds to their zeta potential difference, which demonstrates the quantitative capability of OL-EPM. © 2011 American Institute of Physics.
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| 9.
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論文
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Kobayashi, Naritaka ; Asakawa, Hitoshi ; Fukuma, Takeshi
概要:
Local potential distribution plays important roles in physical, chemical and biological processes at a solid/liquid inte
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rface. However, the measurement of a local potential distribution in liquid has been a long-standing challenge, which has hindered understanding of the mechanisms for the various interfacial phenomena. Recently, we have developed a method to overcome this problem [Kobayashi, Rev. Sci. Instrum. 81, 123705 (2010)], which is referred to as open-loop electric potential microscopy (OL-EPM). Here, we present its first application to quantitative measurements of local potential distribution in liquid. In OL-EPM, an ac bias voltage is applied between a tip and sample and the first and second harmonic cantilever oscillations induced by the electrostatic force are detected and used for the calculation of a potential value. In the equation for the potential calculation, here we introduce a correction factor to cancel out the error caused by the difference in the deflection sensitivity to the first and second harmonic electrostatic forces. With the improved method, we have performed potential measurements of two types of latex beads with different surface charges. The measured potential difference between the different types of latex beads approximately corresponds to their zeta potential difference, which demonstrates the quantitative capability of OL-EPM. © 2011 American Institute of Physics.
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| 10.
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論文
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Fukuma, Takeshi ; Yoshioka, Shunsuke ; Asakawa, Hitoshi
概要:
We have developed a wideband phase-locked loop (PLL) circuit with real-time phase correction for high-speed and accurate
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force measurements by frequency modulation atomic force microscopy (FM-AFM) in liquid. A high-speed operation of FM-AFM requires the use of a high frequency cantilever which, however, increases frequency-dependent phase delay caused by the signal delay within the cantilever excitation loop. Such phase delay leads to an error in the force measurements by FM-AFM especially with a low Q factor. Here, we present a method to compensate this phase delay in real time. Combined with a wideband PLL using a subtraction-based phase comparator, the method allows to perform an accurate and high-speed force measurement by FM-AFM. We demonstrate the improved performance by applying the developed PLL to three-dimensional force measurements at a mica/water interface. © 2011 American Institute of Physics.
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