Gammaretroviruses, such as murine leukemia viruses (MLVs), encode, in addition to the canonical Gag, Pol, and Env proteins that will form progeny virus particles, a protein called “glycogag” (glycosylated Gag). MLV glycogag contains the entire Gag sequence plus an 88-residue N-terminal extension. It has recently been reported that glycogag, like the Nef protein of HIV-1, counteracts the antiviral effects of the cellular protein Serinc5. We have found, in agreement with prior work, that glycogag strongly enhances the infectivity of MLVs with some Env proteins but not those with others. In contrast, however, glycogag was detrimental to MLVs carrying Ebolavirus glycoprotein. Glycogag could be replaced, with respect to viral infectivity, by the unrelated S2 protein of equine infectious anemia virus. We devised an assay for viral entry in which virus particles deliver the Cre recombinase into cells, leading to the expression of a reporter. Data from this assay showed that both the positive and the negative effects of glycogag and S2 upon MLV infectivity are exerted at the level of virus entry. Moreover, transfection of the virus-producing cells with a Serinc5 expression plasmid reduced the infectivity and entry capability of MLV carrying xenotropic MLV Env, particularly in the absence of glycogag. Conversely, Serinc5 expression abrogated the negative effects of glycogag upon the infectivity and entry capability of MLV carrying Ebolavirus glycoprotein. As Serinc5 may influence cellular phospholipid metabolism, it seems possible that all of these effects on virus entry derive from changes in the lipid composition of viral membranes.

Energy transfer between photons and molecules and between neighboring molecules is ubiquitous in living nature, most prominently in photosynthesis. While energy transfer is efficiently utilized by living systems, its adoption to connect individual components in man-made plasmonic nanocircuits has been challenged by low transfer efficiencies that motivate the development of entirely new concepts for energy transfer. We introduce herein optoplasmonic superlenses that combine the capability of optical microcavities to insulate molecule-photon systems from decohering environmental effects with the superior light nanoconcentration properties of nanoantennas. The proposed structures provide significant enhancement of the emitter radiative rate and efficient long-range transfer of emitted photons followed by subsequent refocusing into nanoscale volumes accessible to near-and far-field detection. Optoplasmonic superlenses are versatile building blocks for optoplasmonic nanocircuits and can be used to construct "dark" single-molecule sensors, resonant amplifiers, nanoconcentrators, frequency multiplexers, demultiplexers, energy converters, and dynamical switches.nanophotonics | optical information processing | optical sensing | plasmonics N onradiative energy transfer between nanoobjects is limited to distances of only a few nanometers, making photons the most attractive long-distance signal carriers. However, once the photon is emitted by a donor quantum emitter, the probability of acceptor absorbing its energy becomes negligibly small. Therefore, realizing efficient and controllable on-chip interactions between single photons and single quantum emitters, which are crucial for single-molecule optical sensing and quantum information technology, remains challenging. This problem is mitigated by optical microcavities (OMs), which can significantly boost the probability of a photon reabsorption through acceptor molecules (1) via efficient trapping and recirculating of photons (2). OMs also strongly modify radiative rate of emitters at select frequencies corresponding to cavity modes, which can provide local density of optical states (LDOS) exceeding that of the free space by orders of magnitude (2-5). In turn, noble-metal nanostructures can enhance emission of free-space photons by excited molecules (effectively acting as nano-analogs of radio antennas) (6-12) or facilitate relaxation by coupling to surface plasmons (SPs) (13-15). Consequently, both plasmonic nanostructures and OMs can modify the LDOS (16, 17), but the OM approach suffers from limited accessibility of the intracavity volume by target molecules [which should either be incorporated into the cavity material (3, 4) or interact with photonic modes via their weak evanescent tails (5,(18)(19)(20)], while high dissipative losses in metals create fundamental limitations for long-distance energy and information transfer through surface plasmons (21). Results and DiscussionIn this paper, we develop a previously undescribed approach for photon generation and energy tra...

Efficient delivery of light into nanoscale volumes by converting free photons into localized charge-density oscillations (surface plasmons) enables technological innovation in various fields from biosensing to photovoltaics and quantum computing. Conventional plasmonic nanostructures are designed as nanoscale analogs of radioantennas and waveguides. Here, we discuss an alternative approach for plasmonic nanocircuit engineering that is based on molding the optical powerflow through ‘vortex nanogears’ around a landscape of local phase singularities ‘pinned’ to plasmonic nanostructures. We show that coupling of several vortex nanogears into transmission-like structures results in dramatic optical effects, which can be explained by invoking a hydrodynamic analogy of the ‘photon fluid’. The new concept of vortex nanogear transmissions (VNTs) provides new design principles for the development of complex multi-functional phase-operated photonics machinery and, therefore, generates unique opportunities for light generation, harvesting and processing on the nanoscale.

Despite the extensive use of biodegradable polyester nanoparticles for drug delivery, and reports of the strong influence of nanoparticle mechanics on nano−bio interactions, there is a lack of systematic studies on the mechanics of these nanoparticles under physiologically relevant conditions. Here, we report indentation experiments on poly­(lactic acid) and poly­(lactide-co-glycolide) nanoparticles using atomic force microscopy. While dried nanoparticles were found to be rigid at room temperature, their elastic modulus was found to decrease by as much as 30 fold under simulated physiological conditions (i.e., in water at 37 °C). Differential scanning calorimetry confirms that this softening can be attributed to the glass transition of the nanoparticles. Using a combination of mechanical and thermoanalytical characterization, the plasticizing effects of miniaturization, molecular weight, and immersion in water were investigated. Collectively, these experiments provide insight for experimentalists exploring the relationship between polymer nanoparticle mechanics and in vivo behavior.

Quantum optical coherence tomography (QOCT) makes use of an entangled-photon light source to carry out dispersion-immune axial optical sectioning. We present the first experimental QOCT images of a biological sample: an onion-skin tissue coated with gold nanoparticles. 3D images are presented in the form of 2D sections of different orientations.

Narrow high refractive index nanowires sustain weakly guided modes with significant mode volume outside of the nanowire. This modal spillover makes them interesting photonic materials for a multitude of applications. In this article we fabricate dimers of nanowires with lengths up to 1.4 μm, radii down to 55 nm, and edge-to-edge separation down to 60 nm through anisotropic etching from crystalline silicon (Si). We investigate how the properties of the weakly confined fundamental HE1,1 mode in Si nanowires are modified by their integration into dimers. In particular, we characterize through a combination of experimental spectroscopy and numerical electromagnetic simulations how the lifting of the degeneracy of HE1,1x and HE1,1y modes in dimers of Si nanowires generates linear birefringence, spin angular momentum, and superchirality. Achiral Si nanowire dimers are found to create locations of strongly enhanced near-field chirality in the gap between the nanowires, where the field can interact with the ambient medium.

Viral membranes are nanomaterials whose fluidity depends on their composition, in particular the cholesterol (chol) content. As differences in the membrane composition of individual virus particles can lead to different intracellular fates, biophysical tools capable of sensing the membrane fluidity on the single-virus level are required. In this manuscript, we demonstrate that fluctuations in the polarization of light scattered off gold or silver nanoparticle (NP)-labeled virus-like-particles (VLPs) encode information about the membrane fluidity of individual VLPs. We developed plasmonic polarization fluctuation tracking microscopy (PFTM) which facilitated the investigation of the effect of chol content on the membrane fluidity and its dependence on temperature, for the first time on the single-VLP level. Chol extraction studies with different methyl-β-cyclodextrin (MβCD) concentrations yielded a gradual decrease in polarization fluctuations as function of time. The rate of chol extraction for individual VLPs showed a broad spread, presumably due to differences in the membrane composition for the individual VLPs, and this heterogeneity increased with decreasing MβCD concentration.

We demonstrate a novel approach for fabricating surface enhanced Raman scattering (SERS) substrates for single bacterial biosensing based on Ag cylindrical nanotrough networks (CNNs). This approach is developed with large scalability by leveraging a cellulose nanofiber template fabrication via facile electrospinning. Specifically, a concave nanotrough structure consisting of interconnected concave Ag nanoshells is demonstrated by depositing a thin layer of Ag atop a sacrificial electrospun nanofiber template and then completely removing the cellulose core in water. Our investigations of the scattering properties and SERS performances of single isolated Ag nanotroughs of different diameters reveal that nanotrough-based substrates provide tunable optical responses and enhanced SERS intensities. Further, Ag CNNs are fabricated in highly interconnected networks that yield reproducible SERS signals for molecular monolayers and whole bacterial cells, enabling rapid spectral discrimination between different bacterial strains. Finally, by performing principal component analysis on a large number of measured SERS spectra (40 spectra per bacterium), we demonstrate successful spectral discrimination between two types of Escherichia coli ( E. coli) bacteria, that is, E. coli K12 with its derivative E. coli DH 5α and E. coli BL21(DE3). The demonstrated cost-effective substrates feature several advantages over conventional SERS substrates including environmentally friendly and scalable fabrication compatible with versatile devices and provide an alternative approach to rapid SERS detection and screening of biochemicals.