The Effect of Gold Nanoparticle Surface Modification with Polyethylene Glycol on the Absorbed Dose Distribution upon Irradiation with 137Cs and 60Co Photons

Abstract

Abstract—Modification of the surface of gold nanoparticles with polyethylene glycol (PEG) is widely used to investigate radiosensitization in vivo. This modification may lead to alterations in the spectral characteristics of secondary radiation emitted by gold nanoparticles under the influence of photons. Using a Monte-Carlo calculation, we found that upon irradiation of 17-nm gold nanoparticles coated with a 8.5-nm polyethylene glycol shell with ¹³⁷Cs (E_av = 0.667 MeV) and ⁶⁰Co (E_av = 1.25 MeV) photons, 53.9% (¹³⁷Cs) and 51.3% (⁶⁰Co) of ionization electrons (Auger, Coster–Kronig, and fluorescence), 7.1% (¹³⁷Cs) and 0.9% (⁶⁰Co) of the photoelectrons were absorbed, and 32.6% (¹³⁷Cs) and 27.4% (⁶⁰Co) of the Compton electrons; as well 0.4% (¹³⁷Cs) and 9.7% (⁶⁰Co) of the secondary photons were additionally generated in the polymer shell. The surface modification with polyethylene glycol led to shielding of the high-absorption dose area: the ratio of the absorbed doses for the unmodified and polyethylene glycol-coated gold nanoparticles differed by 1.3–9 times. Since the radiosensitizing efficacy of gold nanoparticles depends on the characteristics of the secondary radiation, the optimization of surface coatings is an important step in rational drug design.