Nanoseries nano zs

NPs’ characteristics, including mean diameter/size distribution profile, polydispersity index (PDI), and zeta potential, were measured using Zetasizer (Nano-series, Nano ZS, model ZEN3600; Malvern Instruments, Worcestershire, UK). Nanoparticles were suspended in water prior to the measurements at 25°C. The drug loading and encapsulation efficiency of the preparation method were evaluated through extraction of docetaxel from freeze-dried PLGA or PLGA–PEG NP formulations. Briefly, acetone was added to 5 mg of NPs to dissolve both polymer and drug. The mixture was vortexed for 30 s and subjected to bath sonication for 30 min. Then, it was centrifuged for 20 min at 1,700× g. The supernatant was separated and preserved. Acetone was added to the precipitate, and the same procedure was repeated. The obtained supernatants from the first and second centrifugation steps were mixed and evaporated. Methanol was added to the residue to precipitate the polymer, vortexed for 30 s, and centrifuged for 20 min at 1,700× g. Docetaxel was then quantified in the supernatant using the mass spectrometry method described later.
Encapsulation efficiency of the preparation method and NPs’ drug loading were then calculated as follows:
$\begin{array}{l}\text{Drug}\text{loading}(\%)=\frac{\text{Weight of drug in particles}}{\text{Weight of particles}}\times 100\\ \text{Drug loading efficiency}(\%)=\frac{\text{Weight of drug in particles}}{\text{Initiail weight of drug added}}\times 100\end{array}$

UV-vis absorbance measurements were performed using a Jasco V-760 spectrophotometer over the wavelength range of 187–800 nm using a 10 mm path length quartz cuvette. Membrane filtration using a Microcon® centrifugal filter with a molecular weight cutoff (MWCO) of 100 kDa was performed to remove unbound, excess dispersants to allow resolution of nanotube absorption feature near 204 nm wavelength. For the measurements shown in Fig. 1, supernatant samples were membrane filtered three times and re-dispersed in water. The concentration of individually dispersed SDC–BNNT complexes was determined using an extinction coefficient of 188.27 mL mg⁻¹ cm⁻¹ at 204 nm wavelength that is obtained in this work. Zeta potential measurements were obtained at room temperature for purified BNNTs stabilized by surfactants using a Malvern Zetasizer Nanoseries Nano-ZS with the dispersions injected into a folded capillary zeta cell. The excess, unbound surfactants were removed by membrane filtration as described previously.