The paper studies the molecular-level active control of localized surface plasmon resonances (LSPRs) of Au nanodisk
arrays with molecular machines. Two types of molecular
machines - azobenzene and rotaxane - have been demonstrated
to enable the reversible tuning of the LSPRs via the controlled mechanical movements. Azobenzene molecules have the
property of trans-cis photoisomerization and enable the photo-induced nematic (N)-isotropic (I) phase transition of the
liquid crystals (LCs) that contain the molecules as dopant. The phase transition of the azobenzene-doped LCs causes the
refractive-index difference of the LCs, resulting in the reversible peak shift of the LSPRs of the embedded Au nanodisks
due to the sensitivity of the LSPRs to the disks' surroundings' refractive index. Au nanodisk array, coated with
rotaxanes, switches its LSPRs reversibly when it is exposed to chemical oxidants and reductants alternatively. The
correlation between the peak shift of the LSPRs and the chemically driven mechanical movement of rotaxanes is
supported by control experiments and a time-dependent density functional theory (TDDFT)-based, microscopic model.
Molecular-ruler nanolithography uses individual molecules as building blocks to create nanometer-scale features in a
low-cost, high-throughput process. Self-assembled multilayers are used in combination with radiation-sensitive
polymeric resists to interface nanometer-scale features with structures fabricated using conventional lithographic
methods. This technique is advantageous for its high precision, parallel processing, and low capital investment. Here,
we provide an overview of molecular-ruler nanolithography and describe how this technology is being applied to the
creation of nanometer-scale devices, patterning of large-area sub-200-nm grating structures, and the fabrication of
quartz templates for use as molds in imprint lithography.
The local structure of biological membranes is critically important to membrane function. Regions of very high positive and negative curvature are found in the membranes of many cells, and rapid changes in membrane curvature are integral parts of many cell activities (e.g. endo/exocytosis, cell crawling, cell division). Our goal is to understand the effects of changes in local membrane structure on membrane properties. Optical tweezers are used to control the local structure of the lipid bilayer by controlling the curvature of the membrane. We use giant (`cell-sized'), thin-walled vesicles as our membrane models. Optically trapped latex microspheres are used to deform the liposome bilayer, forming large areas of altered membrane curvature. In contrast to literature reports in which 514.5 nm light was used in optical trapping, we have not observed adhesion of uncoated latex microspheres to liposome vesicles, nor have we observed signs of rapidly increased osmotic pressure within irradiated vesicles. This indicates that the longer wavelength used in our studies (647.1 nm) is less damaging to biological membranes. Furthermore, optical trapping of vesicles with coexisting gel and fluid phase lipids did not lead to gross changes in domain structure, which would be expected upon laser-induced heating of the membrane.
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