Joshua D. Carter

Enhanced relaxation of nanoparticle-bound supercoiled DNA in X-ray radiation

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.

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.

Silicon-based nanowires from silicon wafers catalyzed by cobalt nanoparticles in a hydrogen environment

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 microm-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.

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.

Damage of supercoiled DNA by an ultrafast laser-driven electron x-ray source.

Using magnetic fields to differentiate the effects of electrons and x-rays, it was discovered that single strand breaks in supercoiled DNA were mainly caused by the energetic ultrafast electrons rather than the ultrafast x-ray photons emitted from the same table-top ultrafast x-ray source. At constant pulse energy of the driving laser pulses, shorter laser pulses produced more strand breaks than longer ones. This was attributed to the increased flux of electrons produced with the shorter laser pulses. Other factors contributing to the DNA damage were investigated and discussed.

DNA Strand Breaks by a Laser-Driven Electron X-ray Source (LEXS)

DNA strand breaks studied with a laser-driven electron x-ray source (LEXS) suggest that ultrafast electrons and x-rays were emitted from this source, and that high energy electrons were mainly responsible for the DNA damage.

More Power to X-Rays: From Ultrafast Dynamics of Metal Complexes to Enhanced Damage to DNA

X-ray spectroscopy was used to investigate charge transfer and subsequent events such as structural rearrangement and radical generation in metal complexes including metal nanoparticles. Several new phenomena were observed and the accompanying mechanisms were investigated.