Enhanced single strand breaks of supercoiled DNA in a matrix of gold nanotubes under X-ray irradiation.

Single-strand-breaks (SSBs) of supercoiled DNA (scDNA) molecules were used to probe the enhancement of X-ray radiation effect on scDNA mixed with gold nanotubes (AuNTs) in water. The amounts of measured enhancements using SSBs were significantly lower than the expected increase in energy deposition in water by AuNTs under hard X-ray irradiation. Three factors were identified to negatively affect the enhancement: (1) Attenuation of kinetic energies carried by electrons escaped from AuNTs, (2) Scavenging of OH radicals (˙OH) by the surface of bare AuNTs, and (3) Steric effect due to soluble scDNA molecules away from the surface of AuNTs. Benefits and limits of using gold nanomaterials as radiation enhancers and contrast agents are discussed.

Chemical enhancement by nanomaterials under X-ray irradiation.

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.

Recognition of melting of nanoparticle catalysts with cubically shaped Co3O4 nanoparticles.

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 degrees C and straight nanowires at 1100 degrees C. Cobalt nanoparticles remained morphologically highly anisotropic after the growth of nanocoils at 1050 degrees C, whereas they became predominately spherical after straight nanowires were made at 1100 degrees 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 degrees C.

Nanoscale energy deposition by X-ray absorbing nanostructures.

Here we wish to demonstrate a unique property of nanomaterials: energy deposition with nanometer precision from low-energy electrons released from these nanostructures interacting with hard X-ray radiation in aqueous solution. Three effects combine to cause this phenomenon: (1) localized absorption of X-rays by nanostructures, (2) effective release of low-energy electrons from small nanostructures, and (3) efficient deposition of energy in water in the form of radicals and electrons. This combination creates localized X-ray absorption and localized energy deposition of nanometer precision. We confirmed the theoretically predicted nanoscale energy deposition distribution by measuring hydroxyl radical-induced DNA strand breaks, and observed enhanced damage to a 5600-bp DNA molecule from approximately 10 chemically conjugated small gold nanoparticles under X-ray radiation. These results provide a general guidance to applications of this new concept in many fields including radiation chemistry, radiology, radiation oncology, biochemistry, biology, and nanotechnology.