The collaborative oscillation of conductive electrons in metal nanoparticles results in a surface plasmon resonance that makes them useful for various applications including biolabeling. We investigate the coupling between pairs of elliptical metal particles by simulations and experiments. The results demonstrate that the resonant wavelength peak of two interacting particles is red-shifted from that of a single particle because of near-field coupling. It is also found that the shift decays approximately exponentially with increasing particle spacing and become negligible when the gap between the two particles exceeds about 2.5 times the particle short-axis length.

SWNTs. We have also investigated the effects of NO 2 and NH 3 on the electrical properties of mats of SWNT ropes made from as-grown laser ablation materials. In a 200-ppm NO 2 flow, the resistance of an SWNT mat is found to decrease from R ϭ 150 to 80 ohms (R before /R after ϳ 2) in ϳ10 min (Fig. 4A). In a 1% NH 3 flow, the resistance of a second SWNT mat increases from 120 to 170 ohms (R after /R before ϳ 1.5) in ϳ10 min (Fig. 4B). In these bulk SWNT samples, the molecular interaction effects are averaged over metallic and semiconducting tubes. Also, the inner tubes in SWNT ropes are blocked from interacting with NO 2 and NH 3 because the molecules are not expected to intercalate into SWNT ropes. This explains the small resistance change of bulk SWNT mats by gas exposure compared to that of an individual S-SWNT.The main feature of individual S-SWNT sensors, besides their small sizes, is that they operate at room temperature with sensitivity as high as 10 3 . An individual nanotube sensor can be used to detect different types of molecules. The selectivity is achieved by adjusting the electrical gate to set the S-SWNT sample in an initial conducting or insulating state. The fast response of a nanotube sensor can be attributed to the full exposure of the nanotube surface area to chemical environments. Thus, nanotube molecular wires should be promising for advanced miniaturized chemical sensors. Single-file diffusion, prevalent in many processes, refers to the restricted motion of interacting particles in narrow micropores with the mutual passage excluded. A single-filing system was developed by confining colloidal spheres in one-dimensional circular channels of micrometer scale. Optical video microscopy study shows evidence that the particle self-diffusion is non-Fickian for long periods of time. In particular, the distribution of particle displacement is a Gaussian function.Single-file diffusion (SFD) occurs when the individual pores of the medium are so narrow that the particles are unable to pass each other (1, 2). The sequence of particles remains unchanged over time, and thus, the basic principle of diffusion as a physical mixing process comes into question. The concept of SFD was originally introduced more than 40 years ago in biophysics to account for the transport of water and ions through molecular-sized channels in membranes (3); since then, in addition to biological systems (4, 5), SFD is also discussed in the context of interaction of Markov chains in statistics (6 ), the transportation of adsorbate molecules through zeolites (2), and charge-carrier migration in one-dimensional (1D) polymer and superionic conductors (7). Furthermore, SFD is also related to surface growth phenomena through some mapping (8).As the mutual passage of particles is prohibited in single-filing (SF) systems, the movements of individual particles are correlated, even at long time periods, because the displacement of a given particle over a long distance necessitates the motion of many other particles in the same direction. This...

We report experimental and theoretical studies on the plasmon resonances of finite one-dimensional chains of Au nanoparticles excited by evanescent light waves with polarization parallel to the chains. The experimental results show that the plasmon resonance peak wavelengths of these finite 1D chains are significantly red-shifted in comparison to that of single Au nanoparticle. Contrary to previous findings, the peak wavelengths are observed to be a nonmonotonic function of particle numbers in the chain. This phenomenon is reproduced in the theoretical results obtained by using the transfer-matrix method and is shown to occur only for larger particles where phase retardation effects are important in plasmon coupling.

Self-propelled bacteria are marvels of nature with a potential to power dynamic materials and microsystems of the future. The challenge is in commanding their chaotic behavior. By dispersing swimming Bacillus subtilis in a liquid-crystalline environment with spatiallyvarying orientation of the anisotropy axis, we demonstrate control over the distribution of bacteria, geometry and polarity of their trajectories. Bacteria recognize subtle differences in liquid crystal deformations, engaging in bipolar swimming in regions of pure splay and bend but switching to unipolar swimming in mixed splay-bend regions. They differentiate topological defects, heading towards defects of positive topological charge and avoiding negative charges. Sensitivity of bacteria to pre-imposed orientational patterns represents a new facet of the interplay between hydrodynamics and topology of active matter.One Sentence Summary: Patterned orientational order controls concentration, trajectories and flows of swimming bacteria in a liquid crystal.

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A new nanophotolithography technique based on the interference of surface plasmon waves is proposed and demonstrated by using computer simulations. The wavelengths of the surface plasmon waves at metal and dielectric interfaces can reach the nanometer scale while their frequencies remain in the optical range. As a result, the resolution of this surface plasmon interference nanolithography (SPIN) can go far beyond the free-space diffraction limit of the light. Simulation results show that one-dimensional and two-dimensional periodical structures of 40-100 nm features can be patterned using interfering surface plasmons launched by 1D gratings. Detailed characteristics of SPIN such as field distribution and contrast are also investigated.

Stimuli-responsive liquid crystal elastomers with molecular orientation coupled to rubber-like elasticity show a great potential as elements in soft robotics, sensing, and transport systems. The orientational order defines their mechanical response to external stimuli, such as thermally activated muscle-like contraction. Here we demonstrate a dynamic thermal control of the surface topography of an elastomer prepared as a coating with a pattern of in-plane molecular orientation. The inscribed pattern determines whether the coating develops elevations, depressions, or in-plane deformations when the temperature changes. The deterministic dependence of the out-of-plane dynamic profile on the in-plane orientation is explained by activation forces. These forces are caused by stretching-contraction of the polymer networks and by spatially varying molecular orientation. The activation force concept brings the responsive liquid crystal elastomers into the domain of active matter. The demonstrated relationship can be used to design coatings with functionalities that mimic biological tissues such as skin.

Eukaryotic cells in living tissues form dynamic patterns with spatially varying orientational order that affects important physiological processes such as apoptosis and cell migration. The challenge is how to impart a predesigned map of orientational order onto a growing tissue. Here, we demonstrate an approach to produce cell monolayers of human dermal fibroblasts with predesigned orientational patterns and topological defects using a photoaligned liquid crystal elastomer (LCE) that swells anisotropically in an aqueous medium. The patterns inscribed into the LCE are replicated by the tissue monolayer and cause a strong spatial variation of cells phenotype, their surface density, and number density fluctuations. Unbinding dynamics of defect pairs intrinsic to active matter is suppressed by anisotropic surface anchoring allowing the estimation of the elastic characteristics of the tissues. The demonstrated patterned LCE approach has potential to control the collective behavior of cells in living tissues, cell differentiation, and tissue morphogenesis.