Understanding the High Longitudinal Relaxivity of Gd(DTPA)-Intercalated (Zn,Al)-Layered Double Hydroxide Nanoparticles.

In this study, biocompatible gadolinium diethylenetriaminepentaacetate (Gd(DTPA))-intercalated (Zn,Al)-layered double hydroxide (LDH) nanoparticles were synthesized, characterized for Gd(DTPA) loading percentage and nanostructure, and the spin-lattice relaxation times (T1) measured to determine their suitability as a potential T1-weighted contrast agent for magnetic resonance imaging (MRI). Compared to the most commonly used contrast agent in clinical MRI (i.e., molecular Gd(DTPA)), significant increases in longitudinal relaxivity (r1) were measured for all Gd(DTPA)-intercalated nanoparticles. For a specific Zn2Al(OH)6(Cl,0.5CO3)0.56Gd(DTPA)0.086·xH2O composition, r1 was found to be 28.38 s-1 mM-1, which is over 6 times the r1 of molecular Gd(DTPA). This dramatic increase in r1 is attributed to (a) the much longer rotational correlation time (τR) of nanoparticles and (b) the inherent water of LDH that forms the second-/outer-sphere in the vicinity of intercalated Gd(DTPA)2-. The latter, with an extensive hydrogen bonding network and insignificant translational motion, results in a longer mean residence lifetime (τM), which makes the contribution of second-/outer-sphere significant. Therefore, when the Gd(DTPA)2- loading percentage increases from 8.6 to 55%, the diminution of the ratio of inherent water to Gd(DTPA)2- concomitantly diminishes the contributions by second-/outer-sphere water to r1. Additionally, the modest increase in r1 with decreasing particle size (∼315-540 nm) is perhaps due to the shortening of τM. Finally, the spin-spin relaxation times (T2) of 17O, determined at various temperatures, show a negligible exchange of water molecules at room temperature. Therefore, the very high r1 of nanoparticles indicate that protons of the bulk water are still accessible to the Gd3+ centers, possibly dominated by prototropic exchange through the hydrogen bonding network.

Vapor-Transport Synthesis and Annealing Study of Zn x Mg1-x O Nanowire Arrays for Selective, Solar-Blind UV-C Detection.

This work uniquely reports the synthesis of Zn x Mg1-x O nanowires and submicron columns by utilizing a traditional carbothermal reduction process toward forming ZnO nanowire ultraviolet detectors, while simultaneously utilizing Mg3N2 as the source of Mg. To investigate the relationship between Mg content in the ZnO lattice and the cutoff wavelength for high spectral responsivity, the nanowires were annealed in a series of designed conditions, whereas chemical, nanostructural, and optoelectronic characteristics were compared before and after treatment. Postanneal scanning electron micrographs revealed a reduction of the average ensemble nanowire dimensions, which was correlated to the modification of ZnO lattice parameters stemming from Zn2+ dissociation and Mg2+ substitution (confirmed via Raman spectroscopy). The analysis of cathodoluminescence spectra revealed a blueshift of the peak alloy band-edge emission along with a redshift of the ZnO band-edge emission; and both were found to be strong functions of the annealing temperature. The conversion of Zn2SiO4 to Mg2SiO4 (in O2) and MgSiO3 (in Ar) was found to correspond to transformations (shifting and scaling) of high-energy luminescence peaks and was confirmed with X-ray diffraction analysis. The tunability of the cutoff photodetection wavelength was evaluated as the nanowire arrays exhibited selective absorption by retaining elevated conduction under high-energy UV-C irradiation after thermal treatment but exhibiting suppressed conductivity and a single order of magnitude reduction in both spectral responsivity (R λ) and photoconductive gain (G) under UV-A illumination. Noise analysis revealed that the variation of detectivity (D*) depended on the regime of ultraviolet irradiation, and that these variations are related to thermal noise resulting from oxygen-related defects on both nanowire and substrate surfaces. These results suggest a minor design tradeoff between the noise characteristics of thermally treated ZnMgO nanowire array UV detectors and the tunability of their spectral sensitivity.

Influence of Protamine Functionalization on the Colloidal Stability of 1D and 2D Titanium Oxide Nanostructures.

The colloidal stability of titanium oxide nanosheets (TNS) and nanowires (TiONW) was studied in the presence of protamine (natural polyelectrolyte) in aqueous dispersions, where the nanostructures possessed negative net charge, and the protamine was positively charged. Regardless of their shape, similar charging and aggregation behaviors were observed for both TNS and TiONW. Electrophoretic experiments performed at different protamine loadings revealed that the adsorption of protamine led to charge neutralization and charge inversion depending on the polyelectrolyte dose applied. Light scattering measurements indicated unstable dispersions once the surface charge was close to zero or slow aggregation below and above the charge neutralization point with negatively or positively charged nanostructures, respectively. These stability regimes were confirmed by the electron microscopy images taken at different polyelectrolyte loadings. The protamine dose and salt-dependent colloidal stability confirmed the presence of DLVO-type interparticle forces, and no experimental evidence was found for additional interactions (e.g., patch-charge, hydrophobic, or steric forces), which are usually present in similar polyelectrolyte-particle systems. These findings indicate that the polyelectrolyte adsorbs on the TNS and TiONW surfaces in a flat and extended conformation giving rise to the absence of surface heterogeneities. Therefore, protamine is an excellent biocompatible candidate to form smooth surfaces, for instance in multilayers composed of polyelectrolytes and particles to be used in biomedical applications.

Insights into the synthesis of layered double hydroxide (LDH) nanoparticles: Part 1. Optimization and controlled synthesis of chloride-intercalated LDH.

Layered double hydroxide (LDH) nanoparticles have excellent anion-intercalating property, and their potential as theranostic nanovectors is high. However, understanding of the control of the mean particle size (MPS) and achievement of monodispersed particle size distribution (PSD) remains elusive. Herein, with the aid of statistical design of experiments on a model system of Cl(-)-intercalated (Zn, Al)-LDH, controlled synthesis of single crystalline nanoparticles using the coprecipitation method followed by hydrothermal treatment (HT) was achieved in three steps. First, a 2(4-1) design enabled the identification of influential parameters for MPS (i.e., salt concentration, molar ratio of carbonate to aluminum, solution addition rate, and interaction between salt concentration and stirring rate) and PSD (i.e., salt concentration and stirring rate), as well as the optimum coprecipitation conditions that result in a monodispersed PSD (i.e., low salt concentration and high stirring rate). Second, a preliminary explanation of the HT was suggested and the optimum HT conditions for obtaining ideal Gaussian PSD with chi-squared (χ(2))<3 were found to be 85°C for 5 h. Third, using a central composite design, a quantitative MPS model, expressed in terms of the significant factors, was developed and experimentally verified to synthesize nearly monodispersed LDH nanoparticles with MPS ∼200-500 nm.

Insights into the synthesis of layered double hydroxide (LDH) nanoparticles: Part 2. Formation mechanisms of LDH.

This study demonstrates the effect of (co)intercalated anion compositions on nanostructure evolution to understand the formation mechanisms of layered double hydroxide (LDH) nanoparticles following coprecipitation and hydrothermal treatments (HT). Initially, the room temperature coprecipitation resulted in amorphous primary nanoparticles that agglomerated at the edges due to low surface charge densities. The reversibility of such agglomeration was determined by the crystalline quality upon HT and consequent surface charge density, which in turn were strongly influenced by the composition of the intercalated anions. Upon crystallization, the agglomerated Zn2Al(OH)6(NO3)0.3(CO3)0.35⋅xH2O primary nanoparticles re-dispersed, but the Zn2Al(OH)6(NO3)⋅xH2O nanoparticles with much lower stability and higher disorder (especially at the edges) exhibited irreversible agglomeration, and transformed into secondary nanoparticles via aggregational growth. Additionally, the stability studies on Zn2Al(OH)6(NO3)y(CO3)0.5(1-y)⋅xH2O nanoparticles (y=0-1) showed that the size difference between the cointercalated anions caused phase separation when 0.9⩾y⩾0.6, leading to bimodal size distributions. Moreover, the coarsening rates were controlled through the cointercalated anion compositions. By gradually varying the ratio of cointercalated NO3(-) to CO3(2-), monodispersed Zn2Al(OH)6(NO3)y(CO3)0.5(1-y)⋅xH2O (0.5⩾y⩾0) nanoparticles with systematic variation in the particle size of ∼200-400nm were obtained after HT at 85°C for 12h.

Inorganic nanoparticles for cancer imaging and therapy.

Inorganic nanoparticles have received increased attention in the recent past as potential diagnostic and therapeutic systems in the field of oncology. Inorganic nanoparticles have demonstrated successes in imaging and treatment of tumors both ex vivo and in vivo, with some promise towards clinical trials. This review primarily discusses progress in applications of inorganic nanoparticles for cancer imaging and treatment, with an emphasis on in vivo studies. Advances in the use of semiconductor fluorescent quantum dots, carbon nanotubes, gold nanoparticles (spheres, shells, rods, cages), iron oxide magnetic nanoparticles and ceramic nanoparticles in tumor targeting, imaging, photothermal therapy and drug delivery applications are discussed. Limitations and toxicity issues associated with inorganic nanoparticles in living organisms are also discussed.

WITHDRAWN: Inorganic nanoparticles for cancer imaging and therapy.

The Publisher regrets that this article is an accidental duplication of an article that has already been published, doi:10.1016/j.jconrel.2011.07.005. The duplicate article has therefore been withdrawn.