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

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

The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Low-loss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces.

All-dielectric metamaterials

Metamaterials are composed of periodic subwavelength metal/dielectric structures that resonantly couple to the electric and/or magnetic components of the incident electromagnetic fields, exhibiting properties that are not found in nature. This class of micro- and nano-structured artificial media have attracted great interest during the past 15 years and yielded ground-breaking electromagnetic and photonic phenomena. However, the high losses and strong dispersion associated with the resonant responses and the use of metallic structures, as well as the difficulty in fabricating the micro- and nanoscale 3D structures, have hindered practical applications of metamaterials. Planar metamaterials with subwavelength thickness, or metasurfaces, consisting of single-layer or few-layer stacks of planar structures, can be readily fabricated using lithography and nanoprinting methods, and the ultrathin thickness in the wave propagation direction can greatly suppress the undesirable losses. Metasurfaces enable a spatially varying optical response (e.g. scattering amplitude, phase, and polarization), mold optical wavefronts into shapes that can be designed at will, and facilitate the integration of functional materials to accomplish active control and greatly enhanced nonlinear response. This paper reviews recent progress in the physics of metasurfaces operating at wavelengths ranging from microwave to visible. We provide an overview of key metasurface concepts such as anomalous reflection and refraction, and introduce metasurfaces based on the Pancharatnam-Berry phase and Huygens' metasurfaces, as well as their use in wavefront shaping and beam forming applications, followed by a discussion of polarization conversion in few-layer metasurfaces and their related properties. An overview of dielectric metasurfaces reveals their ability to realize unique functionalities coupled with Mie resonances and their low ohmic losses. We also describe metasurfaces for wave guidance and radiation control, as well as active and nonlinear metasurfaces. Finally, we conclude by providing our opinions of opportunities and challenges in this rapidly developing research field.

A review of metasurfaces: physics and applications.

Optical metasurfaces have developed as a breakthrough concept for advanced wave-front engineering enabled by subwavelength resonant nanostructures. However, reflection and/or absorption losses as well as low polarization-conversion efficiencies pose a fundamental obstacle for achieving high transmission efficiencies that are required for practical applications. Here, for the first time to our knowledge, highly efficient all-dielectric metasurfaces are demonstrated for NIR frequencies using arrays of silicon nanodisks as metaatoms. The main features of Huygens' sources are employed, namely, spectrally overlapping crossed electric and magnetic dipole resonances of equal strength, to demonstrate Huygens' surfaces with full transmission-phase coverage of 360° and near-unity transmission. Full-phase coverage combined with high efficiency in transmission are experimentally confirmed. Based on these key properties, all-dielectric Huygens' metasurfaces can become a new paradigm for flat optical devices, including beam-steering, beam-shaping, and focusing, as well as holography and dispersion control.

High-Efficiency Dielectric Huygens’ Surfaces

We present the first experimental demonstration of zero backscattering from nanoparticles at optical frequencies as originally discussed by Kerker et al. [ Kerker , M. ; Wang , D. ; Giles , C. J. Opt. Soc. A 1983 , 73 , 765 ]. GaAs pillars were fabricated on a fused silica substrate and the spectrum of the backscattered radiation was measured in the wavelength range 600-1000 nm. Suppression of backscattering occurred at ~725 nm, agreeing with calculations based on the discrete dipole approximation. Particles with zero backscattering provide new functionality for metamaterials and optical antennas.

https://www.photonics.ethz.ch/fileadmin/user_upload/pdf/Papers/person13a-1.pdf

Demonstration of Zero Optical Backscattering from Single Nanoparticles

We present the first experimental demonstration of zero backscattering from nanoparticles at op- tical frequencies as originally discussed by Kerker et. al. [M. Kerker, D. Wang, and C. Giles, J. Opt. Soc. A 73, 765 (1983)]. GaAs pillars were fabricated on a fused silica substrate and the spectrum of the backscattered radiation was measured in the wavelength range 600-1000 nm. Suppression of backscattering occurred at ~725 nm, agreeing with calculations based on the discrete dipole approximation. Particles with zero backscattering provide new functionality for metamaterials and optical antennas.

Demonstration of zero optical backscattering from single nanoparticles

A material-specific dual-color common-path interferometric detection system for discriminating between nanoparticles in solution in real time is described. The detection technique is applicable to situations where both particle size and material are of interest.

/pdf/material-specific-detection-and-classification-of-single-4gevjmzun7.pdf

Material-specific detection and classification of single nanoparticles

GaAs scattering structures are fabricated to measure the suppressed backscattered field due to interference between the electric and magnetic dipole moments.

Steven Person

Papers

Demonstration of Zero Optical Backscattering from Single Nanoparticles

Demonstration of zero optical backscattering from single nanoparticles

Material-specific detection and classification of single nanoparticles

Suppressed backscatter from electric and magnetic dipole interference in sub-micron dielectric spheres