4.8. Cell Irradiation with γ-Rays

In total, 2 × 10⁵ exponentially growing HeLa cells were plated in flask 12 h before irradiation. The cells were incubated with Pt NFs at a Pt concentration of 5 × 10⁻⁴ mol L⁻¹, diluted in cell culture medium for 6 h. The cells were then irradiated by photon beam using a Cesium-137 (E = 0.66 MeV) irradiation system GSR-D1 at Institut Curie, France. After irradiation, cells were washed with PBS, trypsinized, counted and re-seeded into petri dishes at different densities to yield approximately 100 surviving colonies per dish. After 14 days, the colonies were fixed and stained with a 0.5% methylene blue-50% methanol solution. The colony counts were fit with a linear-quadratic model (LQM) by plotting the data on a log (% survival) vs. dose plot in Origin.

Here, SF is the cell surviving fraction, D the irradiation dose and α and β are parameters representing direct lethal and sub-lethal damage, respectively.

We quantified the effect of the NFs utilizing two methods commonly found in the literature. The sensitivity enhancement ratio at 2 Gy (SER_2Gy) is the ratio of SF at 2 Gy for irradiation without and with Pt NFs. The DEF10% is the ratio of doses at 10% survival for irradiation without NFs versus with NFs.