Abstract
Four different gold nanoparticle (GNP) preparations, includingnaked GNPs and GNPs coated either with thiolated undecane (S-C11H23), or with dithiolated diethylenetriaminepentaacetic (DTDTPA) or gadolinium (Gd)DTDTPA chelating agents, were synthesized. The average diameters, for each type ofnanoparticle, are 5 nm, 10 and 13 nm, respectively. Dry films of plasmid DNA pGEM-3Zf(−), DNA with bound GNPs and DNA with coated GNPs were bombardedwith 60 keV electrons. The yields of single and double strand breaks weremeasured as a function of exposure by electrophoresis. The binding of just oneGNP without coating to DNA containing 3197 base pairs increases singleand double strand breaks by a factor of 2.3 while for GNPs coated with S-C11H23 this factor is reduced to 1.6. The GNPs coated with DTDTPA and DTDTPA:Gd in thesame ratio with the DNA, produce essentially no increment in damage. These results couldbe explained by the attenuation by the coatings of the intensity of the low-energyphotoelectrons emitted from the GNPs. Thus, coatings of GNPs may considerablyattenuate the short-range low-energy electrons emitted from gold, leading to a considerabledecrease of radiosensitization. According to our results, the highest radiosensitizationshould be obtained with GNPs having the shortest possible ligand, directed to the DNA ofcancer cells.
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