A Detailed Experimental and Theoretical Investigation on the Chemical and Physical Behavior of Gold Nanoparticles Under X-ray Radiation

Download or read book A Detailed Experimental and Theoretical Investigation on the Chemical and Physical Behavior of Gold Nanoparticles Under X-ray Radiation written by Neal Cheng and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A detailed investigation into the interaction between highly ionizing x-ray radiation and nanomaterials was performed. To begin, a theoretical model of the interactions of the system was created as an attempt to understand the relationship between the nanomaterial and the radiation-generated species. The model spans from the physical regime (10−15s) which includes the physical absorption of x-rays, atomic processes, and electron emission to the diffusion regime (10−10s), during which the chemical species generated from radiolytic cleavage of water diffuses and reacts. A combination of methods was used in the simulation: Monte Carlo, Brownian diffusion, and kinetic rate equations. Several experimental systems were created for the purpose of testing the radio-enhancing effects of nanomaterials and the validity of the model: Firstly, the effects of localized energy deposition by gold nanoparticles were examined in a system consisting of 3 nm gold nanoparticles conjugated to DNA. In this system, single-strand breaks on DNA were used to probe the spatial distribution of energy nanometers around the nanoparticle. A comparison of the local energy deposition by gold nanoparticles versus global energy deposition by water was examined using the model. An additional 150% in DNA strand breaks was observed at 100 mM Tris (2-Amino-2-hydroxymethyl-propane-1,3-diol, represents 5nm diffusion distance), yet according to the model, the energy deposition of 10 gold nanoparticles on a strand of DNA accounts for only an additional 20%. Several explanations were given, such as the different reactivity of radical at short distance, the cross-linking of multiple DNA to a single nanoparticle, and geometric configuration of DNA. Secondly, the effect of remote energy deposition was examined in a system consisting of gold nanotubules and free-floating DNA, containing a composition of 50 wt.% Au/50 wt.% H2O. There was no localized energy deposition due to non-conjugation and a maximum enhancement of 1400% was found at 10 mM Tris, which was inconsistent with the expected enhancement of ~14000%. The result was explained using the scavenging of the radicals by gold nanoparticles, attenuation of the electron energy by the nanotubules, and the proximity of the DNA to the surface. Lastly, gold nanoparticles were found to chemically enhance the conversion of coumarin-3-carboxylic acid (3-CCA) into 7-OHCCA during x-ray radiation. The magnitude of this chemical effect exceeds 1000x the physical absorption of x-rays, therefore ruling out a possible cause from the additional hydroxyl radicals produced by the gold nanoparticles. The size dependency of this effect suggests it is a surface phenomenon. Furthermore, there is a dose rate dependency, which suggests that this effect is dependent on the steady state concentration of a radiation-generated species. We have determined that it is the superoxide radical through reductionist techniques. We have noticed that the enhancement is proportional to superoxide concentrations through creation and elimination of the superoxide radical. By combining experiment and theory, it was determined that the model can successfully predict the radiosensitizing behavior of the previously mentioned systems. It is an excellent tool for further research on radiosensitizing effects of nanomaterials.