Magnetic Particle Imaging (MPI) is an emerging, whole body biomedical imaging technique, with sub-millimeter spatial resolution and high sensitivity to a biocompatible contrast agent consisting of an iron oxide nanoparticle core and a biofunctionalized shell. Successful application of MPI to imaging of cancer depends on the nanoparticles (NPs) accumulating at tumors at sufficient levels relative to other sites. NPs physiochemical properties such as size, crystallographic structure and uniformity, surface coating, stability, blood circulation time and magnetization determine the efficacy of their tumor accumulation and MPI signal generation. Here, we address these criteria by presenting strategies for the synthesis and surface functionalization of efficient MPI tracers, that can target a typical murine brain cancer model and generate three dimensional images of these tumors with very high signal-to-noise ratios (SNR). Our results showed high contrast agent sensitivities that enabled us to detect 1.1ng of iron (SNR~3.9) and enhance the spatial resolution to about 600μm. The biodistribution of these NPs was also studied using near infra-red fluorescent (NIRF) and single-photon emission computed tomography (SPECT) imaging. NPs were mainly accumulated in liver and spleen and did not show any renal clearance. This first pre-clinical study of cancer targeted NPs imaged using a tomographic MPI system in an animal model, paves the way to explore new nanomedicine strategies for cancer diagnosis and therapy, using clinically safe magnetic iron oxide nanoparticles and MPI.

Herein we report the fabrication of ultralight gold aerogel monoliths with tunable densities and pore structures. Gold nanowires are prepared at the gram scale by substrate-assisted growth with uniform size, ultrathin diameters, high purity, and a high aspect ratio. Freeze-casting of suspensions of these nanowires produces free-standing, monolithic aerogels with tunable densities from 6 to 23 mg/cm3, which to the best of our knowledge represents the lowest density monolithic gold material. We also demonstrate that the pore geometries created during freeze-casting can be systematically tuned across multiple length scales by the selection of different solvents and excipients in the feedstock suspension. The mechanical behavior of porous materials depends on relative density and pore architectures.

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An intermediate polymorph of iron oxide, ε-Fe2O3, has attracted significant attention due to its giant coercive field (H c) and potential applications in high-frequency millimeter-wave absorption and high-density magnetic recording. However, the fabrication of ε-Fe2O3 with high phase purity is still a challenge due to complicated synthetic procedures and a large variety of reaction parameters. Here, we have identified critical reaction parameters to improve the phase purity of ε-Fe2O3, and the effects of all possible reaction parameters have been tested through systematic studies. A combination of structural and magnetic characterization techniques provides us with an accurate and reliable phase purity analysis of the ε-Fe2O3 phase. Specifically, we observed that (1) the reaction temperature and time and (2) the addition of Ba are critical parameters to improve the phase purity. We identified the optimal conditions that maximize the coercivity and phase purity, giving insight into the effects of each parameter on the γ- to ε- to α-phase-transition pathway. We obtained nearly single-phase ε-Fe2O3 (∼87 wt % with ∼13 wt % α-phase) with a large coercivity of H c = 20.6 kOe, enabling us to obtain pure ε-Fe2O3 by a simple magnetic separation protocol, and tuned the H c of the ε-Fe2O3 nanoparticles in the range of 4.0–20.6 kOe by controlling the reaction parameters. Furthermore, the structural properties of the resulting ε-Fe2O3 nanoparticles are confirmed by characterizing their chemical and magnetic properties using X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements.

Radiative cooling materials continue to underperform compared to their theoretical potential due to parasitic heating from contact with ambient air. Solutions to this problem are expensive or complex to fabricate. Here, a potentially inexpensive, simply fabricated material that improves cooling performance by reducing parasitic heating was created using naturally abundant salts. NaCl and KCl are not typically considered for radiative cooling because of their high hygroscopicity and low mechanical strength; however, these compounds are highly infrared-transparent and can be fabricated into aerogel-like structures to provide thermally insulating properties. Salt aerogels, described herein, scattered (reflected) visible light, transmitted infrared radiation, and provided thermal insulation. They were packaged into mechanical supporting panels to avoid physical disruption and the nanostructure was stabilized to moisture by adding anti-caking agent. The panels were able to keep an underlying surface below ambient temperature for a full 24-hour cycle and reduced parasitic heating rate by more than half (compared to an uncovered surface). The panels were able to cool a variety of underlying surfaces, even highly absorbing surfaces that are normally well above ambient temperature during the day. This work demonstrates an affordable, easily produced, electricity-free cooling technology with potential to be manufactured for large-scale practical applications.