2.3. Characterization of ZEO-loaded CSNPs
Morphological characteristics of CSNPs and ZEO@CSNPs were
examined by high-resolution transmission electron microscope
(TEM) (Hitachi, H-600) at an accelerating voltage of 100 kV.
Samples were immobilized on copper grids. They were dried under
reduced pressure at an ambient temperature overnight prior to TEM
observation and then were examined using a TEM without being
stained. Particle size was determined by dynamic light scattering
(DLS) using a photon correlation spectroscopy (PCS) assembly
(Zetasizer 3000 HS, Malvern Instruments, UK). Zeta potential was measured
by laser Doppler anemometry on the same instrument. Results
are reported as the mean of three measurements ± SD (standard
deviation). UV-vis absorption spectra were recorded over a wavelength
ranging from 220 to 400 nm by a TECAN spectrometer (infinite M200
Pro, Switzerland).
2.4. Determination of encapsulation efficiency and loading capacity
The percentage of ZEO encapsulated was determined after lysis of
the prepared NPs with hydrochloric acid solution and alcohol, as described
previously (Keawchaoon & Yoksan, 2011). The concentration
of ZEO in absolute alcohol was determined spectrophotometrically at
230 nm (maximum absorption wavelength of ZEO) using a UV-visible
spectrophotometer in triplicate. Encapsulation efficiency (EE) was calculated
through the following relationship: