ROS enhancement by silicon nanoparticles in X-ray irradiated aqueous suspensions and in glioma C6 cells

The capability of silicon nanoparticles to increase the yield of reactive species upon 4 MeV X-ray irradiation of aqueous suspensions and C6 glioma cell cultures was investigated. ROS generation was detected and quantified using several specific probes. The particles were characterized by FTIR, XPS, TEM, DLS, luminescence, and adsorption spec- troscopy before and after irradiation to evaluate the effect of high energy radiation on their structure. The total concentration of O2 •- /HO2 • ,H O • , and H2O2 generated upon 4-MeV X-ray irradiation of 6.4 lM silicon nanoparticle aqueous suspensions were on the order of 10 lM per Gy, ten times higher than that obtained in similar experiments but in the absence of particles. Cytotoxic 1 O2 was generated only in irradi- ation experiments containing the particles. The particle surface became oxidized to SiO2 and the luminescence yield reduced with the irradiation dose. Changes in the surface morphology did not affect, within the experi- mental error, the yields of ROS generated per Gy. X-ray irradiation of glioma C6 cell cultures with incorporated silicon nanoparticles showed a marked production of ROS proportional to the radiation dose received. In the absence of nanoparticles, the cells showed no irradia- tion-enhanced ROS generation. The obtained results indicate that silicon nanoparticles of\5 nm size have the potential to be used as radiosensitizers for improv- ing the outcomes of cancer radiotherapy. Their capa- bility of producing 1 O2 upon X-ray irradiation opens