Here we report the
tuning of a number of excited dye molecules that were strongly coupled
with the localized surface plasmons (LSPs) of Au nanostructures by
electrochemical potential control. Using the redox-state-tuned dye
molecules and several types of metal nanostructures with distinct
LSP energies, active control of the high coupling strength was achieved
via an electrochemical potential-based control method. One interesting
finding of the present work is that the parabolic behavior of the
coupling strength in the range between 0.10 and 0.27 eV is dependent
on the electrochemical potential; this has not been observed previously.
Anticrossing plots showing the energies of the upper and lower states
of the coupling to the LSP energy suggest that the number of dye molecules
contained in the cavity-confined LSP field is controlled not only
by the redox states of the dye molecules but also by the interactions
between the dyes and the metal surfaces. The present finding provides
a novel route to control light–matter interactions regarding
the energy of electrons in metals and molecules, defined by absolute
potential, i.e., electrochemical potential.
Cell polarity determines the direction of cell growth in bacteria. MreB actin spatially regulates peptidoglycan synthesis to enable cells to elongate bidirectionally. MreB densely localizes in the cylindrical part of the rod cell and not in polar regions in Escherichia coli. When treated with A22, which inhibits MreB polymerization, rod-shaped cells became round and MreB was diffusely distributed throughout the cytoplasmic membrane. A22 removal resulted in restoration of the rod shape. Initially, diffuse MreB started to re-assemble, and MreB-free zones were subsequently observed in the cytoplasmic membrane. These MreB-free zones finally became cell poles, allowing the cells to elongate bidirectionally. When MreB was artificially located at the cell poles, an additional pole was created, indicating that artificial localization of MreB at the cell pole induced local peptidoglycan synthesis. It was found that the anionic phospholipids (aPLs), phosphatidylglycerol and cardiolipin, which were enriched in cell poles preferentially interact with monomeric MreB compared with assembled MreB in vitro. MreB tended to localize to cell poles in cells lacking both aPLs, resulting in production of Y-shaped cells. Their findings indicated that aPLs exclude assembled MreB from cell poles to establish cell polarity, thereby allowing cells to elongate in a particular direction.
The intensity of Raman scattering from dye molecules strongly coupled with localized surface plasmons of metal nanostructures was controlled by the electrochemical potential. Through in situ electrochemical extinction and surface-enhanced Raman scattering measurements, it is found that the redox state of the molecules affects the coupling strength, leading to the change in the intensity of the Raman scattering. Analysis of the Raman spectrum provides information on the molecules in strong coupling states showing effective enhancement of Raman scattering.
The light–matter interaction is the crucial tool for the efficient light energy usage. Electrochemical potential control method can tune the coupling strength between the molecules and the light field. In this study, electrochemical surface‐enhanced Raman scattering measurements have been carried out to clarify the detailed molecular behavior in the strong coupling regime. The Raman and fluorescence intensities from dye molecules in the strong coupling regime provided us the information about the change in the distance between the molecules and the metal surface in angstrom level. The detailed investigation of spectra revealed the origin for the potential dependence on the coupling strength. The present insight obtained in the current study would be valuable to understand the electrochemically controlled molecule–light interaction for photochemistry research.
Gram-negative bacteria such as Escherichia coli are surrounded by inner and outer membranes and peptidoglycan in between, protecting the cells from turgor pressure and maintaining cell shape. The Rod complex, which synthesizes peptidoglycan, is composed of various proteins such as a cytoplasmic protein MreB, a transmembrane protein RodZ, and a transpeptidase PBP2. The Rod complex is a highly motile complex that rotates around the long axis of a cell. Previously, we had reported that anionic phospholipids (aPLs; phosphatidylglycerol and cardiolipin) play a role in the localization of MreB. In this study, we identified that cells lacking aPLs slow down Rod complex movement. We also found that at higher temperatures, the speed of movement increased in cells lacking aPLs, suggesting that membrane fluidity is important for movement. Consistent with this idea, Rod complex motion was reduced, and complex formation was disturbed in the cells depleted of FabA or FabB, which are essential for unsaturated fatty acid synthesis. These cells also showed abnormal morphology. Therefore, membrane fluidity is important for maintaining cell shape through the regulation of Rod complex formation and motility.
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