Graphene is a monolayer of tightly packed carbon atoms that possesses many interesting properties and has numerous exciting applications. In this work, we report the antibacterial activity of two waterdispersible graphene derivatives, graphene oxide (GO) and reduced graphene oxide (rGO) nanosheets. Such graphene-based nanomaterials can effectively inhibit the growth of E. coli bacteria while showing minimal cytotoxicity. We have also demonstrated that macroscopic freestanding GO and rGO paper can be conveniently fabricated from their suspension via simple vacuum filtration. Given the superior antibacterial effect of GO and the fact that GO can be mass-produced and easily processed to make freestanding and flexible paper with low cost, we expect this new carbon nanomaterial may find important environmental and clinical applications.

Size and shape of nanoparticles are generally controlled by external influence factors such as reaction temperature, time, precursor, and/or surfactant concentration. Lack of external influence may eventually lead to unregulated growth of nanoparticles and possibly loss of their nanoscale properties. Here we report a gold nanoparticle (AuNPs)-based self-catalyzed and self-limiting system that exploits the glucose oxidase-like catalytic activity of AuNPs. We find that the AuNP-catalyzed glucose oxidation in situ produces hydrogen peroxide (H(2)O(2)) that induces the AuNPs' seeded growth in the presence of chloroauric acid (HAuCl(4)). This crystal growth of AuNPs is internally regulated via two negative feedback factors, size-dependent activity decrease of AuNPs and product (gluconic acid)-induced surface passivation, leading to a rapidly self-limiting system. Interestingly, the size, shape, and catalytic activities of AuNPs are simultaneously controlled in this system. We expect that it provides a new method for controlled synthesis of novel nanomaterials, design of "smart" self-limiting nanomedicine, as well as in-depth understanding of self-limiting systems in nature.

geometrical-optics theory. [ 7 ] Although the intrinsic PSHE was found signifi cantly enhanced by the (spin-independent) phase gradients at carefully designed meta-surfaces (artifi cial ultra-thin metamaterials composed by planar units with tailored properties exhibiting extraordinary capabilities to control light propagations), [8][9][10][11][12][13][14][15][16][17] the measured ratio between the transverse displacement of spin-polarized photons and their traveling distance is still very small (≈10 −2 ). [ 12 ] In a parallel line, strong PSHE was discovered at a particular class of meta-surfaces that can scatter spin-polarized lights to different directions, [13][14][15][16] which is analogous to the extrinsic SHE discovered in electron systems. [ 3 ] The PSHE of this type can be very pronounced because the "transverse forces" acting on the spin-polarized photons come from the (spindependent) phase gradient (comparable to the wave vector of light in vacuum) on the meta-surface, which is realized at subwavelength scales in a fully controllable manner. [13][14][15][16] In sharp contrast to the intrinsic PSHE for which a semi-geometrical-optics theory is suffi cient, [ 12 ] the extrinsic PSHE can only be understood based on the full-wave Maxwell equations where wave interferences play very important roles. [13][14][15][16] However, wave interferences can also form unwanted zero-order modes after scatterings by meta-surfaces, so that the devices realized so far all suffer loweffi ciency problem: typically only a small portion (theoretical limit 25%) of incident spin-polarized photons can be anomalously defl ected by the meta-surfaces yielding the PSHE. [ 14,15,18,19 ] Here we show that in principle a giant PSHE with nearly 100% effi ciency can be realized at meta-surfaces satisfying certain criterion, which is derived from a general Jones matrix analysis. Such a criterion is approachable from two different routes, leading to two types of meta-surfaces with distinct symmetry properties. While the idea is realizable at general frequencies, as a proof of concept, here we design and fabricate two realistic microwave samples and perform experiments to demonstrate that both can realize PSHE with ≈90% effi ciency within a broad frequency bandwidth (≈10-14 GHz). Finally, we experimentally demonstrate that our meta-surfaces can work as effi cient and broadband polarization detectors as one illustration of many potential applications of our fi ndings. Results and Discussion Criterion to Realize PSHE with 100% Effi ciencyWe start from analyzing the electromagnetic (EM) properties of the building block (meta-atom) of our meta-surfaces. As shown in Figure 1 a, consider a generic slab, representing a 2D array Photonic spin Hall effect (PSHE; i.e., spin-polarized photons can be laterally separated in transportation) gains increasing attention from both science and technology, but available mechanisms either require bulky systems or exhibit very low effi ciencies. Here it is demonstrated that a giant PSHE with ≈100% effi ciency can...

DNA hybridization can finely regulate the intrinsic glucose oxidase like catalytic activity of AuNPs owing to the marked difference in adsorption of single‐ and double‐stranded DNA on its surface. A sensing strategy for DNA and microRNA is presented; in a different approach, this DNA‐regulated AuNP catalysis was coupled with AuNP‐mediated seed growth, which was monitored in real time and at a single‐nanoparticle level.

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Durch DNA‐Hybridisierung kann dank des deutlichen Unterschieds in der Adsorption einzel‐ und doppelsträngiger DNA auf der Oberfläche von Au‐Nanopartikeln (AuNPs) deren intrinsische Glucoseoxidase‐artige katalytische Aktivität reguliert werden. Eine Sensorstrategie für DNA und microDNA wurde entwickelt, und außerdem wurde diese DNA‐regulierte AuNP‐Katalyse mit AuNP‐vermitteltem Kristallwachstum gekoppelt, das in Echtzeit auf Einzelpartikelniveau verfolgt wurde.

The unrestricted control of circularly polarized (CP) terahertz (THz) waves is important in science and applications, but conventional THz devices suffer from issues of bulky size and low efficiency. Although Pancharatnam–Berry (PB) metasurfaces have shown strong capabilities to control CP waves, transmission-mode PB devices realized in the THz regime are less efficient, limiting their applications in practice. Here, based on Jones matrix analysis, we design a tri-layer structure (thickness of ~λ/5) and experimentally demonstrate that the structure can serve as a highly efficient transmissive meta-atom (relative efficiency of ~90%) to build PB metadevices for manipulating CP THz waves. Two ultrathin THz metadevices are fabricated and experimentally characterized with a z-scan THz imaging system. The first device can realize a photonic spin Hall effect with an experimentally demonstrated relative efficiency of ~90%, whereas the second device can generate a high-quality background-free CP Bessel beam with measured longitudinal and transverse field patterns that exhibit the nondiffracting characteristics of a Bessel beam. All the experimental results are in excellent agreement with full-wave simulations. Our results pave the way to freely manipulate CP THz beams, laying a solid basis for future applications such as biomolecular control and THz signal transportation.

Controlling the phase distributions on metasurfaces leads to fascinating effects such as anomalous light refraction/reflection, flat-lens focusing, and optics-vortex generation. However, metasurfaces realized so far largely reply on passive resonant meta-atoms, whose intrinsic dispersions limit such passive meta-devices’ performances at frequencies other than the target one. Here, based on tunable meta-atoms with varactor diodes involved, we establish a scheme to resolve these issues for microwave metasurfaces, in which the dispersive response of each meta-atom is precisely controlled by an external voltage imparted on the diode. We experimentally demonstrate two effects utilizing our scheme. First, we show that a tunable gradient metasurface exhibits single-mode high-efficiency operation within a wide frequency band, while its passive counterpart only works at a single frequency but exhibits deteriorated performances at other frequencies. Second, we demonstrate that the functionality of our metasurface can be dynamically switched from a specular reflector to a surface-wave convertor. Our approach paves the road to achieve dispersion-corrected and switchable manipulations of electromagnetic waves.