Nanoparticle characterization

Following purification, all NP formulations were characterized for particle size, polydispersity index (PDI), and surface charge (as measured by ζ-potential) using a Malvern Zetasizer Nano ZS90. Particle size measurements were carried out at a scattering angle of 173°. For ζ-potential, NPs were diluted with 10 mmol/L NaCl solution at pH 7. Transmission electron microscopy (TEM) images were obtained using a Hitachi H7600 microscope. Drug loading was determined using atomic absorption spectroscopy (AAS). Briefly, 10 μL of nanoparticle stock solution was diluted with 990 μL of 2.2% nitric acid, and platinum (Pt) content was measured using an AAnalyst 800 atomic absorption spectrometer (Perkin-Elmer Inc.). A 1.0 mL volume of NP stock solution was then lyophilized in preweighed tubes and subsequently weighed to determine the mass of lyophilized NPs. Drug loading was calculated and reported as wt% (wt cisplatin/wt particles).