A novel method to fabricate a two-dimensional (2D) crystal of protein molecules has been developed. The method enables us to control both the position of nucleation and the direction of the crystal ...growth. The crystal obtained using a protein molecule, ferritin, was found to be composed of a number of densely packed single crystal domains with an unprecedentedly large size of approximately 100 μm2. This method also reveals characteristic behavior of the spatiotemporal evolution of the crystal; for example, “fusion” of the crystal domains, which is never observed in an ordinary crystal composed of atoms or ions, was demonstrated. Our approach could have potential in fabricating extraordinarily large and highly ordered nanoparticle arrays of organic or inorganic materials.
Following the kickoff symposium last year, we will invite out-standing female researchers in the Tsukuba area to hold the 2nd Diversity Symposium. Through the symposium, I would like all members to ...have the opportunity to think about the importance of securing diversity in scnence. The barrier to be overcome is not the “number” of female researchers, but to realize a society where men and women can truly cooperate on equal ground and work together. We look forward to your participation.
This is a special issue for female young scientists and students to explain how large potentials they have in nature. The importance of untiring effort in education to grow new generation is also ...described based on the author's experience. “Anyone who has never made a mistake has never tried anything new” (Albert Einstein) --- The youngers must do challenge in life to obtain what you dream of in your hand.
Electroactive tetrathiafulvalene (TTF)-containing alkanethiol self-assembled monolayers (SAMs) were designed and synthesized to elucidate the relationship between electrochemical responses and film ...structures. Two TTF derivative molecules having one alkanethiol chain (1) and two alkanethiol chains (2) were utilized to modulate the molecular packing arrangements in the SAMs, and the formation and structure of the SAMs were characterized by surface plasmon resonance spectroscopy (SPR). SPR measurements in various contacting media demonstrated loose packing of SAM 1 and close packing of SAM 2 due to the different space fillings of the molecules. Two successive one-electron redox waves were observed for both SAMs by cyclic voltammetry. The peak widths of the redox waves were strongly dependent on the oxidation states of the TTF moieties, the packing arrangement of the SAMs, and the contacting medium. We found that TTF-based SAMs exhibited collective electrochemical responses induced by dynamic structural changes, depending on the degree of freedom for the component molecules in the SAMs. These results imply that the molecular design, taking into account the electrochemical responses, extends the available range of molecular-based functionalities in TTF-based SAMs.
We report a way of using citrates, ionic capping molecules on gold nanoparticles, as a "tuner" to adjust the charge density on the particles by solution pH, in correlation with their association ...constants (pKa). We have synthesized 10% biotin-capped gold nanoparticles with 90% citrates covering on the remaining surfaces. The controlled electrostatic repulsion force between the particles determines the distance between the particles on substrate, i.e., the surface density of the particles, even for the case of immobilization via biotin-avidin reaction. Thus the density of gold nanoparticles on surface was varied in a wide range systematically, especially to high density, and the optical response of two dimensional particle aggregates was investigated to discuss the effect of local plasmon coupling. The UV-vis-Near-IR reflection absorption spectrum of the particle aggregates at low pH (pH < pKa2) appeared with a transverse resonance at ca. lamda=520 nm and a longitudinal resonance widened and red-shifted to lamda=680 nm. Surface plasmon resonance (SPR) curve of the aggregates exhibits a large shift of the minimum angle position together with a significant increase of the minimum intensity (dip-up), as opposed to a small angle shift and no dip-up for well-dispersed particles. The deviation from the SPR simulation curves based on the Maxwell-Garnett (MG) theory clearly indicates the effect of local plasmon coupling in aggregates. The Kramers-Kronig transformations of the UV-vis-Near-IR spectra and the SPR data analyses with Fresnel's equations state the increase of the effective dielectric constants of the particle layers with the density of the particles and the formation of aggregates.
A plasmonic metasurface composed of a self-assembled monolayer of gold nanoparticles allows for fluorescence imaging with high spatial resolution, owing to the collective excitation of localized ...surface plasmon resonance. Taking advantage of fluorescence imaging confined to the nano-interface, we examined actin organization in breast cancer cell lines with different metastatic potentials during cell adhesion. Live-cell fluorescence imaging confined within tens of nanometers from the substrate shows a high actin density spanning < 1 μm from the cell edge. Live-cell imaging revealed that the breast cancer cell lines exhibited different actin patterns during the initial phase of cell adhesion (∼ 1 h). Non-tumorous MCF10A cells exhibited symmetric actin localization at the cell edge, whereas highly metastatic MDA-MB-231 cells showed asymmetric actin localization, demonstrating rapid polarization of MDA-MB-231 cells upon adhesion. The rapid actin organization observed by our plasmonic metasurface-based fluorescence imaging provides information on how quickly cancer cells sense the underlying substrate.
Display omitted
•Live-cell imaging with high lateral and axial resolution was performed.•A plasmonic metasurface confines fluorescence within ∼ 20 nm from substrate.•Actin at cell edge similar to super-resolution microscopy of fixed cells was observed.•Breast cancer cells showed different actin organization within 1 h after attachment.
We have proposed a gold nanoparticle (GNP)-based single-electron transistor (SET) doped with a dye molecule, where the molecule works as a photoresponsive floating gate. Here, we examined the ...source-drain current () at a constant drain voltage under light irradiation with various wavelengths ranging from 400 to 700 nm. Current change was enhanced at the wavelengths of 600 and 700 nm, corresponding to the optical absorption band of the doped molecule (copper phthalocyanine: CuPc). Moreover, several peaks appear in the histograms of during light irradiation, indicating that multiple discrete states were induced in the device. The results suggest that the current change was initiated by the light absorption of CuPc and multiple CuPc molecules near the GNP working as a floating gate. Molecular doping can activate advanced device functions in GNP-based SETs.
Recently we have developed an unsymmetrical azobenzene disulfide with a short alkyl side chain, 4-hexyl-4‘-(12-(dodecyldithio)-dodecyloxy)azobenzene (C6AzSSC12), aiming of a high efficiency in ...photoisomerization in SAMs on planar gold surfaces (Tamada, K.; et al. Langmuir 2002, 18, 5239). In this paper, we introduce an additional modification on the molecule to improve the thermal endurance for the photoreaction by attachment of a methyl group to the azobenzene ring, thus avoiding dye aggregation sterically. A “methyl-derivatized” azobenzenethiol (C6Az(Me)SH) SAM revealed a significant improvement in their photoreactivity compared with an unmodified azobenzenethiol (C6AzSH) SAM due to the steric effect of the methyl group. A “methyl-derivatized” unsymmetrical azobenzene disulfide (C6Az(Me)SSC12) SAM exhibited quite a similar photoresponse to that of C6AzSSC12 SAM before heat treatment owing to the free volume given by the unsymmetrical structure; however, only the C6Az(Me)SSC12 SAM could retain high photoreactivity in phase-segregated domains formed by annealing, unlike the C6AzSSC12 SAM. The C6Az(Me)SH and C6Az(Me)SSC12 SAMs exhibited a reaction kinetics different from that of C6AzSSC12 SAM due to a different quantum yield and the molecular tilt angle of the azobenzene unit. The C6Az(Me)SH SAM exhibited a typical character of “congested surface”, where the reaction rate from cis to trans was faster, while that from trans to cis was slower compared with those of C6Az(Me)SSC12 SAM.
Display omitted
► We synthesize protein and temperature-responsive polymer conjugates. ► We examine the adsorption of protein–polymer conjugates on a surface. ► The adsorption of the conjugates is ...control by temperature and surfactants. ► The adsorption profile depends on temperature change in the presence of surfactant.
Ferritin grafted with temperature-responsive poly(N-isopropylacrylamide) (PIPAAm-ferritin) was synthesized by a coupling reaction using PIPAAm and ferritin for obtaining stimuli-responsive biomaterials. The hydrodynamic diameter of PIPAAm-ferritins in aqueous solution increased at 37°C at a higher protein concentration (>0.2mg/mL) because of the intermolecular aggregation through the hydrophobic interaction of PIPAAm chains. On the other hand, PIPAAm-ferritins at a lower concentration (<0.2mg/mL) were unable to increase their size even at 37°C. The adsorption kinetics of PIPAAm-ferritins on hydrophobically modified Si substrate were evaluated with a quartz crystal microbalance in 10mmol/L Bis–Tris/HCl buffer (pH 5.8) with and without poly(oxyethylene) sorbitan monolaurate (TWEEN 20) (0.05wt%) as a surfactant. Although the adsorption of PIPAAm-ferritins on hydrophobic Si substrate at 25°C in the buffer with TWEEN 20 was hardly observed, PIPAAm-ferritins were considerably adsorbed on the substrate at 37°C, indicating that the hydrophobic interaction between the substrate and PIPAAm grafts on the ferritins after the destruction of the hydrophobic interaction between the protein and the substrate by TWEEN 20.
PDF
