2.5. Plasma Stability Study

The colloidal stability of DSF loaded N-NPs, TAT-NPs, and PGlu-PEG/TAT-NPs in plasma was evaluated through a transmittance study as described previously [27]. Briefly, 0.5 mL of DSF-loaded formulations were diluted with 2 mL PBS containing 50% rat plasma, respectively. Rat plasma was collected from the whole blood of Sprague-Dawley (SD) rats. The whole blood was treated with sodium heparin, then vortexed for 30 s and centrifuged at 6000 rpm for 10 min to extract the supernate as rat plasma. PGlu-PEG/TAT-NPs was further divided to two groups separately against PBS at pH 7.4 and 6.5 containing 50% rat plasma. The transmittance of the formulations was determined at 660 nm at predetermined intervals.

Additionally, the stability of DSF in different nanoparticles evaluated by the residual content of DSF. Briefly, 0.5 mL of DSF-loaded formulations were added into rat plasma (2 mL) in tubes at 37 °C with a shaking rate of 100 rpm. At predetermined intervals, aliquots of 200 μL were withdrawn, treated with 200 μL of acetonitrile, and vortexed for 1 min. The mixture solution was centrifuged at 12,000 rpm for 10 min at 4 °C. The supernatant was collected and analyzed to determine the DSF. DSF solution was prepared by dissolving DSF in Cremophor EL/ethanol and was then diluted with saline.