Shape-changing nanomagnets: A new approach to in vivo biosensing

The idea that optical color can be determined by size and shape is well known at the nanoscale. Colors of quantum dots and plasmonic nanostructures, for example, can be tuned through particle size and shape. Among others, this has directly enabled many different multi-colored nanoparticle labels that underpin a host of optically-based in vitro bioimaging applications, including multiplexed high-throughput bioassays and colorimetric sensing and visualization of biomolecular processes and function. Imaging and sensing in more realistic in vivo environments is more challenging, however. Optical probes can be sized or shaped to yield resonances closer to the more optically favorable near-infrared window, but optical penetration, signal intensity, and spatial resolution, still deteriorate rapidly with increasing depth beneath the surface. But what about in the radio-frequency (RF) portion of the spectrum? Are there any analogous nanoparticle structures that can shift the frequency, or equivalently color, of RF signals for which penetration and/or distortion through biological tissue would no longer be a limitation and where imaging and sensing would be naturally immune to any photostability, phototoxicity, and autofluoresence background issues? Please click Additional Files below to see the full abstract

Large T1 contrast enhancement using superparamagnetic nanoparticles in ultra-low field MRI

Superparamagnetic iron oxide nanoparticles (SPIONs) are widely investigated and utilized as magnetic resonance imaging (MRI) contrast and therapy agents due to their large magnetic moments. Local field inhomogeneities caused by these high magnetic moments are used to generate T2 contrast in clinical high-field MRI, resulting in signal loss (darker contrast). Here we present strong T1 contrast enhancement (brighter contrast) from SPIONs (diameters from 11 nm to 22 nm) as observed in the ultra-low field (ULF) MRI at 0.13 mT. We have achieved a high longitudinal relaxivity for 18 nm SPION solutions, r1 = 615 s−1 mM−1, which is two orders of magnitude larger than typical commercial Gd-based T1 contrast agents operating at high fields (1.5 T and 3 T). The significantly enhanced r1 value at ultralow fields is attributed to the coupling of proton spins with SPION magnetic fluctuations (Brownian and Néel) associated with a low frequency peak in the imaginary part of AC susceptibility (χ”). SPION-based T1-weighted ULF MRI has the advantages of enhanced signal, shorter imaging times, and iron-oxidebased nontoxic biocompatible agents. This approach shows promise to become a functional imaging technique, similar to PET, where low spatial resolution is compensated for by important functional information

Interface deformations affect the orientation transition of magnetic ellipsoidal particles adsorbed at fluid-fluid interfaces

Manufacturing new soft materials with specific optical, mechanical and magnetic properties is a significant challenge. Assembling and manipulating colloidal particles at fluid interfaces is a promising way to make such materials. We use lattice-Boltzmann simulations to investigate the response of magnetic ellipsoidal particles adsorbed at liquid-liquid interfaces to external magnetic fields. We provide further evidence for the first-order orientation phase transition predicted by Bresme and Faraudo [Journal of Physics: Condensed Matter 19 (2007), 375110]. We show that capillary interface deformations around the ellipsoidal particle significantly affect the tilt-angle of the particle for a given dipole-field strength, altering the properties of the orientation transition. We propose scaling laws governing this transition, and suggest how to use these deformations to facilitate particle assembly at fluid-fluid interfaces.Comment: 7 pages, 8 figure

Large T1 contrast enhancement using superparamagnetic nanoparticles in ultra-low field MRI

Superparamagnetic iron oxide nanoparticles (SPIONs) are widely investigated and utilized as magnetic resonance imaging (MRI) contrast and therapy agents due to their large magnetic moments. Local field inhomogeneities caused by these high magnetic moments are used to generate T2 contrast in clinical high-field MRI, resulting in signal loss (darker contrast). Here we present strong T1 contrast enhancement (brighter contrast) from SPIONs (diameters from 11 nm to 22 nm) as observed in the ultra-low field (ULF) MRI at 0.13 mT. We have achieved a high longitudinal relaxivity for 18 nm SPION solutions, r1 = 615 s−1 mM−1, which is two orders of magnitude larger than typical commercial Gd-based T1 contrast agents operating at high fields (1.5 T and 3 T). The significantly enhanced r1 value at ultralow fields is attributed to the coupling of proton spins with SPION magnetic fluctuations (Brownian and Néel) associated with a low frequency peak in the imaginary part of AC susceptibility (χ”). SPION-based T1-weighted ULF MRI has the advantages of enhanced signal, shorter imaging times, and iron-oxidebased nontoxic biocompatible agents. This approach shows promise to become a functional imaging technique, similar to PET, where low spatial resolution is compensated for by important functional information