抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Plasmons in strongly coupled metallic nanostructures.

基礎講座 電気泳動(Electrophoresis)

The resonant modes of plasmonic nanoparticle structures made of gold or silver endow them with an ability to manipulate light at the nanoscale. However, owing to the high light losses caused by metals at optical wavelengths, only a small fraction of plasmonics applications have been realized. Kuznetsov et al. review how high-index dielectric nanoparticles can offer a substitute for these metals, providing a highly flexible and low-loss route to the manipulation of light at the nanoscale.

Science , this issue p. [10.1126/science.aag2472][1]

 [1]: /lookup/doi/10.1126/science.aag2472

http://science.sciencemag.org/content/sci/354/6314/aag2472.full.pdf

Optically resonant dielectric nanostructures

Metasurfaces are planar structures that locally modify the polarization, phase and amplitude of light in reflection or transmission, thus enabling lithographically patterned flat optical components with functionalities controlled by design. Transmissive metasurfaces are especially important, as most optical systems used in practice operate in transmission. Several types of transmissive metasurface have been realized, but with either low transmission efficiencies or limited control over polarization and phase. Here, we show a metasurface platform based on high-contrast dielectric elliptical nanoposts that provides complete control of polarization and phase with subwavelength spatial resolution and an experimentally measured efficiency ranging from 72% to 97%, depending on the exact design. Such complete control enables the realization of most free-space transmissive optical elements such as lenses, phase plates, wave plates, polarizers, beamsplitters, as well as polarization-switchable phase holograms and arbitrary vector beam generators using the same metamaterial platform.

/pdf/dielectric-metasurfaces-for-complete-control-of-phase-and-3pa0oy7av0.pdf

Dielectric metasurfaces for complete control of phase and polarization with subwavelength spatial resolution and high transmission

We demonstrate that coupling between grating diffraction and localized surface plasmons in two-dimensional gold nanoparticle arrays in water leads to narrow near-infrared resonance peaks in measured far field extinction spectra. Good agreement is obtained between finite difference time domain (FDTD) calculations and experimental extinction spectra. The FDTD calculations predict that the gold nanoparticle arrays exhibit near-field electric field intensity (E2) enhancements approximately one order of magnitude greater than those of single isolated gold nanoparticles.

/pdf/experimental-observation-of-narrow-surface-plasmon-4940919z11.pdf

Experimental observation of narrow surface plasmon resonances in gold nanoparticle arrays

Although optical tweezers based on far-fields have proven highly successful for manipulating objects larger than the wavelength of light, they face difficulties at the nanoscale because of the diffraction-limited focused spot size. This has motivated interest in trapping particles with plasmonic nanostructures, as they enable intense fields confined to sub-wavelength dimensions. A fundamental issue with plasmonics, however, is Ohmic loss, which results in the water, in which the trapping is performed, being heated and to thermal convection. Here we demonstrate the trapping and rotation of nanoparticles using a template-stripped plasmonic nanopillar incorporating a heat sink. Our simulations predict an ~100-fold reduction in heating compared with previous designs. We further demonstrate the stable trapping of polystyrene particles, as small as 110 nm in diameter, which can be rotated around the nanopillar actively, by manual rotation of the incident linear polarization, or passively, using circularly polarized illumination.

/pdf/trapping-and-rotating-nanoparticles-using-a-plasmonic-nano-3oxpe577zz.pdf

Trapping and rotating nanoparticles using a plasmonic nano-tweezer with an integrated heat sink

We demonstrate that vertical silicon nanowires take on a surprising variety of colors covering the entire visible spectrum, in marked contrast to the gray color of bulk silicon. This effect is readily observable by bright-field microscopy, or even to the naked eye. The reflection spectra of the nanowires each show a dip whose position depends on the nanowire radii. We compare the experimental data to the results of finite difference time domain simulations to elucidate the physical mechanisms behind the phenomena we observe. The nanowires are fabricated as arrays, but the vivid colors arise not from scattering or diffractive effects of the array, but from the guided mode properties of the individual nanowires. Each nanowire can thus define its own color, allowing for complex spatial patterning. We anticipate that the color filter effect we demonstrate could be employed in nanoscale image sensor devices.

/pdf/multicolored-vertical-silicon-nanowires-19n9pau35t.pdf

Multicolored vertical silicon nanowires

We demonstrate optically trapping of microparticles on silicon microring resonators. Once trapped on a microring, a particle can be confined in an optical potential with a depth of 25 k(B)T over the entire microring's circumference. The particles are propelled around the microring at hundreds of micrometers per second, producing periodic revolutions at a few hertz. We anticipate that the increased force and highly accurate positioning obtainable with this system will lead to various nanomanipulation applications.

/pdf/optical-manipulation-with-planar-silicon-microring-38isg5ufum.pdf

Optical Manipulation with Planar Silicon Microring Resonators

A nanowire array is described herein. The nanowire array comprises a substrate and a plurality of nanowires extending essentially vertically from the substrate; wherein: each of the nanowires has uniform chemical along its entire length; a refractive index of the nanowires is at least two times of a refractive index of a cladding of the nanowires. This nanowire array is useful as a photodetector, a submicron color filter, a static color display or a dynamic color display.

Ethan Schonbrun

Papers

Experimental observation of narrow surface plasmon resonances in gold nanoparticle arrays

Trapping and rotating nanoparticles using a plasmonic nano-tweezer with an integrated heat sink

Multicolored vertical silicon nanowires

Optical Manipulation with Planar Silicon Microring Resonators

Light absorption and filtering properties of vertically oriented semiconductor nano wires