Noble metal nanoparticles have been extensively studied to understand and apply their plasmonic responses, upon coupling with electromagnetic radiation, to research areas such as sensing, photocatalysis, electronics, and biomedicine. The plasmonic properties of metal nanoparticles can change significantly with changes in particle size, shape, composition, and arrangement. Thus, stabilization of the fabricated nanoparticles is crucial for preservation of the desired plasmonic behavior. Because plasmonic nanoparticles find application in diverse fields, a variety of different stabilization strategies have been developed. Often, stabilizers also function to enhance or improve the plasmonic properties of the nanoparticles. This review provides a representative overview of how gold and silver nanoparticles, the most frequently used materials in current plasmonic applications, are stabilized in different application platforms and how the stabilizing agents improve their plasmonic properties at the same time. Specifically, this review focuses on the roles and effects of stabilizing agents such as surfactants, silica, biomolecules, polymers, and metal shells in colloidal nanoparticle suspensions. Stability strategies for other types of plasmonic nanomaterials, lithographic plasmonic nanoparticle arrays, are discussed as well. CONTENTS 1. Introduction 664 2. Synthesis of Ag and AuNPs and Stabilization with Adsorbed/Covalently Attached Ligands in Solution Phase 666 2.1. Theoretical Background of Colloidal Stability of the Plasmonic Nanoparticles 667 2.2.

Vitrification, a kinetic process of liquid solidification into glass, poses many potential benefits for tissue cryopreservation including indefinite storage, banking, and facilitation of tissue matching for transplantation. To date, however, successful rewarming of tissues vitrified in VS55, a cryoprotectant solution, can only be achieved by convective warming of small volumes on the order of one mL. Successful rewarming requires both uniform and fast rates in order to reduce thermal mechanical stress and cracks, and to prevent rewarming phase crystallization. Here we present a scalable nanowarming technology for 1 to 80 mL samples using radiofrequency-excited mesoporous silica coated iron oxide nanoparticles in VS55. Advanced imaging including Sweep Imaging with Fourier Transform and micro computed tomography were used to verify loading and unloading of VS55 and nanoparticles and successful vitrification of human dermal fibroblast cells, porcine arteries, and porcine aortic heart valve leaflet tissue. Nanowarming was then used to demonstrate uniform and rapid rewarming at > 130 °C/min in both physical (1 to 80 mL) and biological systems (1 to 50 mL). Nanowarming yielded viability that matched control and/or exceeded gold standard convective warming in 1 to 50 mL systems, and improved viability compared to slow warmed (crystallized) samples. Finally, biomechanical testing displayed no significant biomechanical property changes in blood vessel length or elastic modulus after nanowarming compared to untreated fresh control porcine arteries. In aggregate, these results demonstrate new physical and biological evidence that nanowarming can improve the outcome of vitrified cryogenic storage of tissues in larger sample volumes.

Aggregation is a known consequence of nanoparticle use in biology and medicine; however, nanoparticle characterization is typically performed under the pretext of well-dispersed, aqueous conditions. Here, we systematically characterize the effects of aggregation on the alternating magnetic field induced heating and magnetic resonance (MR) imaging performance of iron oxide nanoparticles (IONPs) in non-ideal biological systems. Specifically, the behavior of IONP aggregates composed of ~10 nm primary particles, but with aggregate hydrodynamic sizes ranging from 50 nm to 700 nm, was characterized in phosphate buffered saline and fetal bovine serum suspensions, as well as in gels and cells. We demonstrate up to a 50% reduction in heating, linked to the extent of aggregation. To quantify aggregate morphology, we used a combination of hydrodynamic radii distribution, intrinsic viscosity, and electron microscopy measurements to describe the aggregates as quasifractal entities with fractal dimensions in the 1.8–2.0 range. Importantly, we are able to correlate the observed decrease in magnetic field induced heating with a corresponding decrease in longitudinal relaxation rate (R1) in MR imaging, irrespective of the extent of aggregation. Finally, we show in vivo proof-of-principle use of this powerful new imaging method, providing a critical tool for predicting heating in clinical cancer hyperthermia.

We investigate nuclear magnetic resonance (NMR) in near-zero-field, where the Zeeman interaction can be treated as a perturbation to the electron mediated scalar interaction (J-coupling). This is in stark contrast to the high field case, where heteronuclear J-couplings are normally treated as a small perturbation. We show that the presence of very small magnetic fields results in splitting of the zero-field NMR lines, imparting considerable additional information to the pure zero-field spectra. Experimental results are in good agreement with first-order perturbation theory and with full numerical simulation when perturbation theory breaks down. We present simple rules for understanding the splitting patterns in near-zero-field NMR, which can be applied to molecules with non-trivial spectra.PACS numbers: 82.56. Fk, 33.25.+k, 71.70.Ej, 33.57.+c Nuclear magnetic resonance experiments are typically performed in high magnetic fields, on the order of 10 T in order to maximize chemical shifts and to achieve high nuclear spin polarization and efficient detection via inductive pickup. The advent of various pre-or hyperpolarization schemes, and alternative methods of detection based on superconducting quantum interference devices (SQUIDs) [1] or atomic [2, 3] magnetometers has enabled NMR experiments in very low (≈earth's field) and even zero magnetic field, generating significant experimental [4][5][6][7][8][9][10][11][12][13][14][15][16] and theoretical interest [12,17,18]. Low-field NMR carries the advantage of providing high absolute field homogeneity, yielding narrow resonance lines and accurate determination of coupling parameters [9,14]. Further, elimination of cryogenically cooled superconducting magnets facilitates the development of portable devices for chemical analysis and imaging. In this regard, atomic magnetometers are an ideal tool because, in contrast to SQUIDs, they do not require cryogenic cooling. Recent work using atomic magnetometers to detect NMR was performed at zero field, in part, because of the need to match the resonance frequencies of the nuclear spins and the magnetometer's alkali spins, which have very different gyromagnetic ratios [14,16]. It has been pointed out that zero-field NMR leaves some ambiguity in determination of chemical groups, and that this ambiguity can be removed by application of small magnetic fields [17].Here, we examine, experimentally and theoretically, the effects of small magnetic fields in near-zero-field * Electronic address: ledbetter@berkeley.edu (NZF) NMR. We show that application of weak magnetic fields results in splitting of the zero-field (ZF) lines, restoring information about gyromagnetic ratios that is lost in ZF NMR. In the regime where the Zeeman effect can be treated as a perturbation, we observe highresolution spectra with easy-to-understand splitting patterns that are in good qualitative and quantitative agreement with first-order perturbation theory. This work represents the first observation of NMR under such conditions, forming the basis for a n...