Determining arterial macrophage expression is an important goal in the molecular imaging of atherosclerosis. Here we compare the efficacy of two synthetic, HDL-based contrast agents for magnetic resonance imaging (MRI) of macrophage burden. Each form of HDL was labeled with gadolinium and rhodamine to allow MRI and fluorescence microscopy. Either the 37 or 18 amino acid peptide replaced the apolipoprotein A-I in these agents, which were termed 37pA-Gd or 18A-Gd. The diameters of 37pA-Gd and 18A-Gd are 7.6 nm and 8.0 nm, respectively, while the longitudinal relaxivities are 9.8 and 10.0 (mMs) -1 . 37pA has better lipid binding properties. In vitro tests with J774A.1 macrophages proved the particles possessed the functionality of HDL by eliciting cholesterol efflux and were taken up in a receptor-like fashion by the cells. Both agents produced enhancements in atherosclerotic plaques of apolipoprotein E knockout mice of ~90% (n=7 per agent) and are macrophage specific as evidenced by confocal microscopy on aortic sections. The half-lives of 37pA-Gd and 18A-Gd are 2.6 and 2.1 hours, respectively. Despite the more favorable lipid interactions of 37pA, both agents gave similar, excellent contrast for the detection of atherosclerotic macrophages using MRI. Supporting Information AvailableThe method for macrophage efflux determination and further details of the MRI scanning setup can be found online. Furthermore, figures displaying the uptake of 18A-Gd and 37pA-Gd in macrophages as a function of time (S1 and S2), the uptake of Gd-micelles in macrophages as a function of concentration (S3) and a confocal microscopy image of the aorta of an apoE mouse where there are no macrophages (S4) are included in the supporting information. This material is available free of charge via the Internet at http://pubs.acs.org/.

Coherent nanoscale photon sources are of paramount importance to achieving all-optical communication. Several nanolasers smaller than the diffraction limit have been theoretically proposed and experimentally demonstrated using plasmonic cavities to confine optical fields. Such compact cavities exhibit large Purcell factors, thereby enhancing spontaneous emission, which feeds into the lasing mode. However, most plasmonic nanolasers reported so far have employed resonant nanostructures and therefore had the lasing restricted to the proximity of the resonance wavelength. Here, we report on an approach based on gold nanorod hyperbolic metamaterials for lasing. Hyperbolic metamaterials provide broadband Purcell enhancement due to large photonic density of optical states, while also supporting surface plasmon modes to deliver optical feedback for lasing due to nonlocal effects in nanorod media. We experimentally demonstrate the advantage of hyperbolic metamaterials in achieving lasing action by its comparison with that obtained in a metamaterial with elliptic dispersion. The conclusions from the experimental results are supported 2 with numerical simulations comparing the Purcell factors and surface plasmon modes for the metamaterials with different dispersions. We show that although the metamaterials of both types support lasing, emission with hyperbolic samples is about twice as strong with 35% lower threshold vs. the elliptic ones. Hence, hyperbolic metamaterials can serve as a convenient platform of choice for nanoscale coherent photon sources in a broad wavelength range. TOC GraphicWe study lasing in two gold nanorod arrays coated with Rhodamine 101, one exhibiting hyperbolic dispersion at the lasing wavelength, the other with elliptic dispersion. Experiments show the hyperbolic metamaterial provides stronger emission with reduced threshold. 3Since its invention in 1960 1 , the laser has seen tremendous developments and has quickly revolutionized fundamental and applied fields such as metrology, medicine, data storage, fabrication and telecommunications among others 2 . With the ever growing need for data transfer speeds and compact devices, several efforts have been made in miniaturizing the laser for on-chip integration 3-7 . While photonic cavities have proven to exhibit high-Q factors enabling strong lasing, their miniaturization to the nanoscale is not viable since the diffraction limit requires the cavity length to be at least half the lasing wavelength [8][9][10] . In contrast, plasmonic cavities, which can be employed to achieve optical amplification and lasing action with charge oscillations, have successfully led to the design of coherent photon sources no longer limited by the diffraction limit 10 . Coupling of emitters with the strongly confined electromagnetic fields associated with plasmonic oscillations can significantly enhance spontaneous emission in certain modes, a process known as the Purcell effect 11 . This effect yields a redistribution of spontaneous emission over wavevector space ...

Plasmonic titanium nitride nanostructures are obtained via nitridation of titanium dioxide. Results show that complex nano‐ and microscale designs of refractory plasmonic nitrides can be realized by utilizing the well‐understood oxide material synthesis. Large‐scale 3D nanoarchitectures will enable the use of refractory plasmonic materials in a variety of areas including spectrally and angularly selective metamaterials, plasmon‐enhanced photocatalysis, and photothermal systems.