Nanosilver becomes labile upon entering the human body or the environment. This lability creates silver species with antimicrobial properties that make nanosilver attractive as active components in many consumer products, wound dressings, and agricultural applications. Because lability depends strongly on morphology, it is imperative to use a material with constant lability throughout kinetic studies so that accurate lability data can be acquired with efficient detection. Here 2.5 nm thick silver was coated onto 90-nm diameter gold nanosphere cores and this surface silver layer was gradually removed by either chemical or X-ray radiation etching. The most sensitive region of a sigmoidal surface plasmon resonance (SPR) response as a function of silver thickness was found for the first time between 0.9- and 1.6-nm thick silver, revealing a new nanosilver standard for lability studies. The SPR peak position detection sensitivity is 8 nm (SPR peak shift)/nm (silver thickness change) within this steepest region of the plasmon response curve whereas outside, sensitivity drops to 1 nm/nm. Since the centroid of SPR profiles can be discerned with 0.25 nm precision, the 8-nm/nm sensitivity means it is possible to detect a 0.3-angstrom or sub-monolayer change in silver thickness. The SPR response simulated by discrete dipole approximation (DDA) was an identical sigmoidal function between 0 and 2 nm of silver coating. These findings were supported by several other analytical measurements, which confirmed no silver recoating during these etching processes.

Nanomaterials can enhance the effect of X-rays, but the mechanisms of enhancement can be complicated. Electron paramagnetic resonance (EPR) was used here to shed light on enhancement mechanisms by detecting the originally proposed physical enhancement of the effect of X-rays by as-made large gold nanoparticles. Specifically spin trap reagent 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO) was used to trap radicals produced in aqueous solutions under X-ray irradiation. Even though only BMPO hydroxyl adducts were detected at the time of EPR measurement, both hydroxyl and superoxide radicals were found to contribute to the enhancement. The measured total enhancement was 0.7-fold per weight percent (wp) of Au in water using unfiltered X-rays. The theoretically predicted physical enhancement is 0.49 fold per wp of gold in water. This information, together with scavenging experimental results and the fact that the G-values are close for both radicals, suggest that hydroxyl and superoxide radicals contributing almost equally to the total measured enhancement. Further, the enhancement was found to be linearly dependent on the amount of large gold nanoparticles in water and no additional radical was produced beyond the amount predicted by type 1 physical enhancement, indicating that hydroxyl or superoxide radicals were not produced via catalytic pathways.

A nanoscale probe of calcium phosphate enclosed liposomes filled with sulforhodamine B (SRB) aqueous solution was synthesized, and the degradation of SRB in the probes was used to measure the enhanced energy deposition within the nanoscale probes after mixing them with PEGylated gold nanoparticles under X-ray irradiation. The enhancement was measured as a function of the gold nanoparticle concentration, and the results showed a surprising jump at 0.46 nM of gold nanoparticles with a steep slope of 42-fold per one weight percentage (wp–1) of gold in water superimposed on a gentle 1-fold wp–1 slope. Theoretical simulations revealed that the jump was caused by the previously proposed type 2 physical enhancement (T2PE) exerted from a single 90 nm gold nanoparticle on a contacting nanoscale probe, and the gentler slope by type 1 physical enhancement (T1PE) was caused by the rest of the gold nanoparticles hundreds of nanometers or farther away. The jump is equivalent to a 2-fold absolute enhancement for each nanoscale probe. This assignment also suggests that T1PE and T2PE obey the addition algorithm. The use of nanoscale probes creates a framework of X-ray-induced energy transfer in which both T1PE and T2PE can be understood as energy transfer from gold nanoparticle donors to nanoscale probe acceptors.

Following a 6-h inhalation exposure to aerosolized 20 and 110 nm diameter silver nanoparticles, lung tissues from rats were investigated with X-ray absorption spectroscopy, which can identify the chemical state of silver species. Lung tissues were processed immediately after sacrifice of the animals at 0, 1, 3, and 7 days post exposure and the samples were stored in an inert and low-temperature environment until measured. We found that it is critical to follow a proper processing, storage and measurement protocol; otherwise only silver oxides are detected after inhalation even for the larger nanoparticles. The results of X-ray absorption spectroscopy measurements taken in air at 85 K suggest that the dominating silver species in all the postexposure lung tissues were metallic silver, not silver oxide, or solvated silver cations. The results further indicate that the silver nanoparticles in the tissues were transformed from the original nanoparticles to other forms of metallic silver nanomaterials and the rate of this transformation depended on the size of the original nanoparticles. We found that 20 nm diameter silver nanoparticles were significantly modified after aerosolization and 6-h inhalation/deposition, whereas larger, 110 nm diameter nanoparticles were largely unchanged. Over the seven-day postexposure period the smaller 20 nm silver nanoparticles underwent less change in the lung tissue than the larger 110 nm silver nanoparticles. In contrast, silica-coated gold nanoparticles did not undergo any modification processes and remained as the initial nanoparticles throughout the 7-day study period.

The total enhancement obtained from mixing silica-covered 90 nm gold nanoparticles and tetrakis (hydroxymethyl) phosphonium-covered 2 nm gold nanoparticles that individually under X-ray irradiation produced average physical enhancement and chemical enhancement respectively was studied experimentally and theoretically. The total or combined enhancement was shown to be the multiplication of the two individual enhancements, and this algorithm can be derived from the original definition of physical and chemical enhancement. The maximum total enhancement was 18-fold, whereas the maximum measured average physical enhancement was 7-fold and the derived chemical enhancement was 3.9-fold; all three maxima were achieved under different experimental conditions. The results of simulation using rate equations for the combined physical and chemical enhancement were obtained and were found to agree with the measured total enhancements.

The absolute optical power at 611 nm emitting from Eu doped Gd2O3 nano phosphors upon X-ray excitation from a microfocus X-ray source operated at 100 kV was measured with thin film photovoltaic cells (TFPCs), whose optical response was calibrated using an He–Ne laser at 632 nm. The same TFPCs were also used to determine the absorbed X-ray power by the nano phosphors. These measurements provided a convenient and inexpensive way to determine the absolute quantum efficiency of nano phosphors, normally a difficult task. The measured absolute X-ray-to-optical fluorescence efficiency of the nano phosphors annealed at 1100 °C was 3.2%. This is the first time such efficiency for Eu/Gd2O3 nano phosphors is determined, and the measured efficiency is a fraction of the theoretically predicted maximum efficiency of 10% reported in the literature.

We for the first time used highly water-soluble silica-covered gold nanoparticles (AuNP@SiO2) in water to successfully isolate average physical enhancement from other enhancements such as nanoscale physical enhancement, chemical enhancement, and antienhancement and obtained the highest enhancement slope of 1.03 per weight percent (wp–1) and the highest experimental enhancement factor of 4.5-fold (εexpt = 4.5 and εexpt= 0 for no enhancement) at 7.5 wp of gold in water. The slope and εexpt agree with the theoretically predicted values obtained from simulation of enhancement of X-rays by gold nanoparticles in water, and the experimental enhancement coefficient (γ = εexpt/εtheo, 0 ≤ γ ≤ 1) is approximately 0.90. The enhancement dependency on X-ray energy, silica layer thickness, and sample thickness were studied experimentally and theoretically. The results presented here elucidate the mechanism of the average physical enhancement by nanomaterials under X-ray irradiation.

Enhanced cellular toxicity was observed using X-ray irradiated nanoparticle drug carriers (NDC) consisting of doxorubicin (DOX) conjugated to DNA strands attached to the surface of gold nanoparticles. Kinetic studies showed that X-rays, acting as a triggering modality, generated reactive oxygen species to break DNA strands and release DOX.

We report here a new phenomenon of dynamic enhancement of chemical reactions by nanomaterials under hard X-ray irradiation. The nanomaterials were gold and platinum nanoparticles, and the chemical reaction employed was the hydroxylation of coumarin carboxylic acid. The reaction yield was enhanced 2000 times over that predicted on the basis of the absorption of X-rays only by the nanoparticles, and the enhancement was found for the first time to depend on the X-ray dose rate. The maximum turnover frequency was measured at 1 × 10–4 s–1 Gy–1. We call this process chemical enhancement, which is defined as the increased yield of a chemical reaction due to the chemical properties of the added materials. The chemical enhancement described here is believed to be ubiquitous and may significantly alter the outcome of chemical reactions under X-ray irradiation with the assistance of nanomaterials.

We demonstrated for the first time enhanced formation of polymers on nanostructures under X-ray irradiation. Surface enhanced Raman spectroscopy (SERS) using silver core–gold shell nanocoreshells (Ag@Au NCSs) as the SERS substrate was employed to quantify the amount of polymers on the surface. The yield of surface-grown polyaniline (PANI) from X-ray-irradiated aniline monomers in aqueous solution of the NCSs was 28 times that of aniline-mixed NCSs without X-rays or 400 times that with the monomers alone irradiated with X-rays. The enhancement was dose rate-dependent and is believed to originate from Ag/Au ionic species created from X-ray generated hydroxyl radicals (•OH) reacting with NCSs. The resulting Ag/Au ionic species on NCSs then initiate PANI formation from aniline molecules absorbed on the NCS surface. The results presented here help advance a new field of X-ray nanochemistry and may inspire applications requiring X-ray-triggered formation of polymers on nanomaterials.Keywords: chemical enhancement; nanomaterials; physical enhancement; polyaniline; polymerization; X-ray nanochemistry; X-rays;

A theorem is established to show that nanoscale energy deposition in water by X-rays can be greatly enhanced via the geometry of nanostructures. The calculated results show that enhancement over background water can reach over 60 times for a single nanoshell made of gold. Other geometries and nanostructures are investigated, and it is found that a shell of gold nanoparticles can generate similar enhancement. The concepts of composition, matrix, and satellite effects are established and studied, all of which can further increase the enhancement of the effect of X-rays.

Monodisperse platinum nanoparticles between 2 and 8 nanometers were synthesized to help quantitatively investigate the size dependency and the activity of surface sites for steam reforming of methane reaction to produce hydrogen gas. It was observed that these monodisperse nanoparticles aggregated to almost double the size of nanoparticles after a few hours of steam reforming reactions at high temperatures. Using the size of nanoparticles determined by transmission electron microscopy and the measured turnover frequencies for these monodisperse nanoparticles, it was found, for the first time, that the activity of these nanoparticles of different sizes for steam reforming of methane can be described mathematically using only two variables of the type and the coordination number of the surface atoms.Keywords (keywords): catalysis; nanoparticles; size dependency; steam reforming of methane; turnover frequency; turnover rate;

Cubically shaped cobalt oxide nanoparticle catalysts were used for the first time to investigate the melting of the nanoparticle catalysts responsible for the synthesis of silica nanocoils at 1050 °C and straight nanowires at 1100 °C. Cobalt nanoparticles remained morphologically highly anisotropic after the growth of nanocoils at 1050 °C, whereas they became predominately spherical after straight nanowires were made at 1100 °C. These results strongly indicated that cobalt nanoparticles responsible for the synthesis of straight nanowires were completely molten and that melting occurred to these nanoparticles between 1050 and 1100 °C.Transformation of cubically shaped cobalt nanoparticle catalysts from room temperature to 1100 °C: The reduction occurs at below 600 °C, and total melting occurs between 1050 and 1100 °C.

We investigated the catalytic reaction of CO 2 reforming of methane (CRM) using as-made Ni/Co nanoparticles believed to be immobilized at the tips of single-walled carbon nanotubes (SWNTs). It was found that under the reforming conditions used in this work the turnover rate of the Ni/Co-SWNT catalytic material for CRM was tens to hundreds of times greater than the best existing CRM catalysts. Combined with the long lifetime of this new catalyst, its total turnover times for CRM were significantly greater than those of any other existing CRM catalysts.

Narrow size distribution Ni nanocrystals with average diameters from 5 to 13 nm (∼20% standard deviation) and a face-centered cubic (fcc) structure were synthesized via rapid thermo-decomposition in the presence of surfactants in solution. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize these nanocrystals. It was found that the solvent determined the rate of the decomposition of Ni precursors, while the surfactants controlled the size and shape of Ni nanocrystals. A three-step process was proposed to explain the synthesis. The purified Ni nanocrystals readily formed micrometer-sized ring structures on TEM grids after solvent evaporation (hexanes), and the magnetic field was found to increase the density of the rings.

A therapeutic methodology was developed based on the large X-ray absorption cross-section of gold nanoparticles at high photon energies (>81 keV). Experimental results showed that the amounts of the relaxed circular supercoiled DNA (scDNA) for gold nanoparticle-bound scDNA were more than doubled compared to that for free scDNA under otherwise identical radiation conditions.

We present here the synthesis of silicon-based nanowires directly from silicon wafers at high temperatures and in the presence of cobalt nanoparticles and hydrogen gas. All three ingredients were critical to the growth of Si-based nanowires, which were between 5–60 nm in diameter and µm–mm long. Both heavily coiled and straight Si-based nanowires were made. Experimental evidence suggested that the sources of silicon for the nanowires growth were in the gas phase.

Enhanced cellular toxicity was observed using X-ray irradiated nanoparticle drug carriers (NDC) consisting of doxorubicin (DOX) conjugated to DNA strands attached to the surface of gold nanoparticles. Kinetic studies showed that X-rays, acting as a triggering modality, generated reactive oxygen species to break DNA strands and release DOX.