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Anti-freezing surfactants form an adsorption layer at the solid-water interface to inhibit the nucleation and growth of ice. However, this mechanism has not been elucidated at the molecular scale because of the difficulties in visualizing such adsorption structures. In this study, we overcome this limitation by directly visualizing the three-dimensional (3D) adsorption structures of anti-freezing surfactants, hexadecyltrimethylammonium bromide (C

Funding Information: The authors gratefully acknowledge financial support by Grants‐in‐Aid for Scientific Research (Nos. 20H00345 and 20K05321) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (MEXT). This work was also partly funded by JSTMirai Program (No. 18077272). The authors thank the World Premier International Research Center Initiative (WPI); MEXT, Japan; and the Kanazawa University Fund (Strategic Research Promotion Program, Core‐to‐Core Program). The authors also acknowledge financial support from the Sumitomo Foundation (No. 190382), the Natural Sciences and Engineering Research Council (NSERC Canada) (Discovery Grant F16‐05032). This work was a part of the Academy of Finland's Flagship Programme under Projects No. 318890 and 318891 (Competence Center for Materials Bioeconomy, FinnCERES) and also Project No. 314862. Computing resources from the Aalto Science‐IT project and CSC, Helsinki are gratefully acknowledged. Publisher Copyright: © 2022 The Authors. Small Methods published by Wiley-VCH GmbH. Chitin is one of the most abundant and renewable natural biopolymers. It exists in the form of crystalline microfibrils and is the basic structural building block of many biological materials. Its surface crystalline structure is yet to be reported at the molecular level. Herein, atomic force microscopy (AFM) in combination with molecular dynamics simulations reveals the molecular-scale structural details of the chitin nanocrystal (chitin NC)–water interface. High-resolution AFM images reveal the molecular details of chitin chain arrangements at the surfaces of individual chitin NCs, showing highly ordered, stable crystalline structures almost free of structural defects or disorder. 3D-AFM measurements with submolecular spatial resolution demonstrate that chitin NC surfaces interact strongly with interfacial water molecules creating stable, well-ordered hydration layers. Inhomogeneous encapsulation of the underlying chitin substrate by these hydration layers reflects the chitin NCs’ multifaceted surface character with different chain arrangements and molecular packing. These findings provide important insights into chitin NC structures at the molecular level, which is critical for developing the properties of chitin-based nanomaterials. Furthermore, these results will contribute to a better understanding of the chemical and enzymatic hydrolysis of chitin and other native polysaccharides, which is also essential for the enzymatic conversion of biomass.

Adhesion of silica abrasive nanoparticles to a poly(vinyl alcohol) (PVA) brush surface in post-CMP (chemical–mechanical planarization) cleaning leads to serious problems in yield enhancement of sem...

Stimuli-responsive polyelectrolyte brushes adapt their physico-chemical properties according to pH and ion concentrations of the solution in contact. We synthesized a poly(acrylic acid) bearing cysteine residues at side chains and a lipid head group at the terminal, and incorporated them into a phospholipid monolayer deposited on a hydrophobic silane monolayer. The ion-specific, nanoscale response of polyelectrolyte brushes was detected by using three-dimensional scanning force microscopy (3D-SFM) combined with frequency modulation detection. The obtained topographic and mechanical landscapes indicated that the brushes were uniformly stretched, undergoing a gradual transition from the brush to the bulk electrolyte in the absence of divalent cations. When 1 mM calcium ions were added, the brushes were uniformly compacted, exhibiting a sharper brush-to-bulk transition. Remarkably, the addition of 1 mM cadmium ions made the brush surface significantly rough and the mechanical landscape highly heterogeneous. Currently, cadmium-specific nanoscale compaction of the brushes is attributed to the coordination of thiol and carboxyl side chains with cadmium ions, as suggested for naturally occurring, heavy metal binding proteins.

We have investigated the calcite growth mechanism by directly imaging atomic-scale structural changes at the growing step edges with high-speed frequency modulation atomic force microscopy (HS-FM-AFM). We compared the results with those previously obtained during dissolution, where a transition region (TR) consisting of a Ca(OH)

Atomic force microscopy (AFM) is the only technique that allows label-free imaging of nanoscale biomolecular dynamics, playing a crucial role in solving biological questions that cannot be addressed by other major bioimaging tools (fluorescence or electron microscopy). However, such imaging is possible only for systems either extracted from cells or reconstructed on solid substrates. Thus, nanodynamics inside living cells largely remain inaccessible with the current nanoimaging techniques. Here, we overcome this limitation by nanoendoscopy-AFM, where a needle-like nanoprobe is inserted into a living cell, presenting actin fiber three-dimensional (3D) maps, and 2D nanodynamics of the membrane inner scaffold, resulting in undetectable changes in cell viability. Unlike previous AFM methods, the nanoprobe directly accesses the target intracellular components, exploiting all the AFM capabilities, such as high-resolution imaging, nanomechanical mapping, and molecular recognition. These features should greatly expand the range of intracellular structures observable in living cells.

The helical structures of poly(diphenylacetylene)s bearing optically active substituents linked through amide bonds and with a helicity memory have been visualised using atomic force microscopy. The polymers self-assembled into an ordered 2D monolayer on highly oriented pyrolytic graphite upon exposure to solvent vapour, whose helical pitch and handedness (right- and left-handed) were for the first time directly revealed at molecular resolution.

Calcite dissolution plays critical roles in the global carbon cycle in the Earth, biomineralizations, and weathering of buildings. However, in spite of the importance, the atomistic events at the step edges during the dissolution have remained elusive because of the difficulties in their direct visualization. In this study, we used high-speed frequency modulation atomic force microscopy (FM-AFM) for visualizing various atomic-scale step edge structures and dynamics during the calcite dissolution in water. The obtained images reveal the coexistence of the steps with and without a transition region (TR); a Ca(OH)2 monolayer formed along the step edge as an intermediate state in the dissolution. The TRs are more frequently observed along the slowly dissolving acute steps than along the rapidly dissolving obtuse steps. This finding and our imaging of the TR formation process suggest that the free energy to form a TR is comparable to that for removing ions directly from the step edge and an increase in the loc...

Calcite dissolution is initiated by the formation of a nanoscale etch pit followed by step edge propagation and hence strongly influenced by the interactions between surface diffusing ions and step edges. However, such atomic-scale dynamics are mostly inaccessible with current imaging tools. Here, we overcome this limitation by using our recent development of high-speed frequency modulation atomic force microscopy. By visualizing atomic-scale structural changes of the etch pits at the calcite surface in water, we found the existence of mobile and less-mobile surface adsorption layers (SALs) in the etch pits. We also found that some etch pits maintain their size for a long time without expansion, and their step edges are often associated with less-mobile SALs, suggesting their step stabilization effect.

A phase-locked loop (PLL) circuit is the central component of frequency modulation atomic force microscopy (FM-AFM). However, its response speed is often insufficient, and limits the FM-AFM imaging speed. To overcome this issue, we propose a PLL design that enables high-speed FM-AFM. We discuss the main problems with the conventional PLL design and their possible solutions. In the conventional design, a low-pass filter with relatively high latency is used in the phase feedback loop, leading to a slow response of the PLL. In the proposed design, a phase detector with a low-latency high-pass filter is located outside the phase feedback loop, while a subtraction-based phase comparator with negligible latency is located inside the loop. This design minimizes the latency within the phase feedback loop and significantly improves the PLL response speed. In addition, we implemented PLLs with the conventional and proposed designs in the same field programmable gate array chip and quantitatively compared their performances. The results demonstrate that the performance of the proposed PLL is superior to that of the conventional PLL: 165 kHz bandwidth and 3.2 μs latency in water. Using this setup, we performed FM-AFM imaging of calcite dissolution in water at 0.5 s/frame with true atomic resolution. The high-speed and high-resolution imaging capabilities of the proposed design will enable a wide range of studies to be conducted on various atomic-scale dynamic phenomena at solid–liquid interfaces.

金沢大学ナノ生命科学研究所, The microscopic understanding of the crystal growth and dissolution processes have been greatly advanced by the direct imaging of nanoscale step flows by atomic force microscopy (AFM), optical interferometry, and X-ray microscopy. However, one of the most fundamental events that govern their kinetics, namely, atomistic events at the step edges, have not been well understood. In this study, we have developed high-speed frequency modulation AFM (FM-AFM) and enabled true atomic-resolution imaging in liquid at ∼1 s/frame, which is ∼50 times faster than the conventional FM-AFM. With the developed AFM, we have directly imaged subnanometer-scale surface structures around the moving step edges of calcite during its dissolution in water. The obtained images reveal that the transition region with typical width of a few nanometers is formed along the step edges. Building upon insight in previous studies, our simulations suggest that the transition region is most likely to be a Ca(OH)2 monolayer formed as an intermediate state in the dissolution process. On the basis of this finding, we improve our understanding of the atomistic dissolution model of calcite in water. These results open up a wide range of future applications of the high-speed FM-AFM to the studies on various dynamic processes at solid-liquid interfaces with true atomic resolution. © 2017 American Chemical Society., Embargo Period 12 months

Investigating interfacial water ordering on solid surfaces with different hydrophobicities is fundamentally important. Here, we prepared hydrophilic mica substrates with some areas covered by mildly hydrophobic graphene layers and studied the resulting hydration layers using three-dimensional (3D) force measurements based on frequency-modulation atomic force microscopy. Hydration layers of 0.3–0.6 nm were detected on bare graphene regions; these layers were considerably larger than the spacing measured on mica (0.2–0.3 nm). On the graphene-covered regions, we also observed the formation of special ordered structures of adsorbates over time, on which, surprisingly, no prominent hydration layers were detected. Based on these findings, we present one possible scenario to describe the formation process of the ordered interfacial structures and the enhanced oscillation period in the force profiles. This work also demonstrates the capability and significance of 3D force measurements in probing hydration behaviors on a heterogeneous substrate with a lateral resolution smaller than several nanometers.

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor regulating the expression of genes involved in xenobiotic response. Recent studies have suggested that AhR plays essential roles not only in xenobiotic detoxification but also energy metabolism. Thus, in this study, we studied the roles of AhR in lipid metabolism. Under high fat diet (HFD) challenge, liver-specific AhR knock-out (AhR LKO) mice exhibited severe steatosis, inflammation, and injury in the liver. Gene expression analysis and biochemical study revealed that de novo lipogenesis activity was significantly increased in AhR LKO mice. In contrast, induction of suppressor of cytokine signal 3 (Socs3) expression by HFD was attenuated in the livers of AhR LKO mice. Rescue of the Socs3 gene in the liver of AhR LKO mice cancelled the HFD-induced hepatic lipotoxicities. Promoter analysis established Socs3 as novel transcriptional target of AhR. These results indicated that AhR plays a protective role against HFD-induced hepatic steatosis and the subsequent lipotoxicity effects, such as inflammation, and that the mechanism of protection involves the direct transcriptional regulation of Socs3 expression by AhR.

It seems natural to assume that defects at mineral surfaces critically influence interfacial processes such as the dissolution and growth of minerals in water. The experimental verification of this claim, however, is challenging and requires real-space methods with utmost spatial resolution, such as atomic force microscopy (AFM). While defects at mineral-water interfaces have been resolved in 2D AFM images before, the perturbation of the surrounding hydration structure has not yet been analyzed experimentally. In this Letter, we demonstrate that point defects on the most stable and naturally abundant calcite (10.4) surface can be resolved using high-resolution 3D AFM-even within the fifth hydration layer. Our analysis of the hydration structure surrounding the point defect shows a perturbation of the hydration with a lateral extent of approximately one unit cell. These experimental results are corroborated by molecular dynamics simulations.

openaire: EC/FP7/610446/EU//PAMS Frequency modulation atomic force microscopy (FM-AFM) experiments were performed on the calcite (1014) surface in pure water, and a detailed analysis was made of the 2D images at a variety of frequency setpoints. We observed eight different contrast patterns that reproducibly appeared in different experiments and with different measurement parameters. We then performed systematic free energy calculations of the same system using atomistic molecular dynamics to obtain an effective force field for the tip-surface interaction. By using this force field in a virtual AFM simulation we found that each experimental contrast could be reproduced in our simulations by changing the setpoint, regardless of the experimental parameters. This approach offers a generic method for understanding the wide variety of contrast patterns seen on the calcite surface in water, and is generally applicable to AFM imaging in liquids.

金沢大学ナノ生命科学研究所, Recently, there have been significant advancements in liquid-environment atomic force microscopy (AFM) with true atomic resolution. The technical advancements are followed by a rapid expansion of its application area. Examples include subnanometer-scale imaging of biological systems and three-dimensional measurements of water distributions (i.e., hydration structures) and fluctuating surface structures. However, to continue this progress, we should improve the fundamental performance of liquid-environment dynamic-mode AFM. The present AFM technique does not allow real-time imaging of atomic-scale dynamic phenomena at a solid-liquid interface. This has hindered atomic-level understanding of crystal growth and dissolution, catalytic reactions and metal corrosion processes. Improvement in force sensitivity is required not only for such a high-speed imaging but also for various surface property measurements using a high-resolution AFM technique. In this review, we summarize recent works on the improvements in the force sensitivity and operation speed of atomic-resolution dynamic-mode AFM for liquid-environment applications. © 2015 The Japan Society of Applied Physics., Embargo Period 12 months

金沢大学ナノ生命科学研究所, High-speed atomic force microscopy has attracted much attention due to its unique capability of visualizing nanoscale dynamic processes at a solid/liquid interface. However, its usability and resolution have yet to be improved. As one of the solutions for this issue, here we present a design of a high-speed Z-tip scanner with screw holding mechanism. We perform detailed comparison between designs with different actuator size and screw arrangement by finite element analysis. Based on the design giving the best performance, we have developed a Z tip scanner and measured its performance. The measured frequency response of the scanner shows a flat response up to ∼10 kHz. This high frequency response allows us to achieve wideband tip-sample distance regulation. We demonstrate the applicability of the scanner to high-speed atomic-resolution imaging by visualizing atomic-scale calcite crystal dissolution process in water at 2 s/frame.

金沢大学ナノ生命科学研究所, Recent advancement in dynamic-mode atomic force microscopy (AFM) has enabled its operation in liquid with atomic-scale resolution. However, its imaging speed has often been too slow to visualize atomic-scale dynamic processes. Here, we propose a method for making a significant improvement in the operation speed of dynamic-mode AFM. In this method, we use a wideband and low-latency phase detector with an improved algorithm for the signal complexification. We demonstrate atomic-scale imaging of a calcite crystal growth process in water at one frame per second. The significant improvement in the imaging speed should enable various studies on unexplored atomic-scale interfacial processes. © 2013 AIP Publishing LLC.

金沢大学ナノ生命科学研究所, We have developed a liquid-environment atomic force microscope with a wideband and low-noise scanning system for atomic-scale imaging of dynamic processes at solid/liquid interfaces. The developed scanning system consists of a separate-type scanner and a wideband high-voltage amplifier (HVA). By separating an XY-sample scanner from a Z-tip scanner, we have enabled to use a relatively large sample without compromising the high resonance frequency. We compared various cantilever- and sample-holding mechanisms by experiments and finite element analyses for optimizing the balance between the usability and frequency response characteristics. We specifically designed the HVA to drive the developed scanners, which enabled to achieve the positioning accuracy of 5.7 and 0.53 pm in the XY and Z axes, respectively. Such an excellent noise performance allowed us to perform atomic-resolution imaging of mica and calcite in liquid. Furthermore, we demonstrate in situ and atomic-resolution imaging of the calcite crystal growth process in water. © 2013 AIP Publishing LLC.