*3.5. Serum Stability of the <sup>225</sup>Ac-rHDL System*

The <sup>225</sup>Ac-rHDL system (150 <sup>µ</sup>L) was added to 5 mL of diluted human serum (5×). The solutions (*n* = 3) were incubated at 37 ◦C for 10 days. A total of 1 mL of sample was taken at 24, 72, 144, and 240 h to evaluate the stability of the nanosystem. To each sample, 300 µL of TFA was added for protein precipitation. Samples were centrifuged at 1200× *g* for 5 min. The activity (measured in a in a well-type scintillation NaI(Tl) detector) obtained in the sediment corresponded to <sup>225</sup>Ac-rHDL, and the activity in the supernatant, to the free fraction of <sup>225</sup>Ac3+ leaked from the rHDL nanosystem.
