Fig. 4. In vitro radiation enhancement by AuNPs with different sizes. PC3pip and PC3flu cells were incubated with both PSMA-targeted (T) and non-targeted (NT) AuNPs with sizes of (a) 2 nm, (b) 5 nm and (c) 19 nm for 24 h and irradiated with X-ray at 2 Gy, 4 Gy and 6 Gy. (d) Radiation enhancing factor (REF, ratio of eradicated cells with and without AuNPs) for PC3pip cells incubated with PSMA-targeted AuNPs at radiation doses of 2 Gy, 4 Gy and 6 Gy. Data are presented as mean ± SD (n = 3), and differences between groups are compared with two-tailed t-tests, *p ≤ 0.05 **p ≤ 0.01.