Preparation and characterization of nanoparticles
The results of DLS indicated that there was no significant difference
between the particle size of NPsA, NPsB and NPsAB (the hydrodynamic
diameter of NPsA, NPsB and NPsAB was about 82, 94 and 88 nm
respectively). However, the hydrodynamic diameter of the nanoparticles
increased after being conjugated with siRNA and PTX (Fig. 4). For
example, the particle size of the NPsA increased from 88 nm to 120 nm
after being encapsulated with siRNA and PTX. The surface charge of NPsA,
NPsB and NPsAB was significantly reduced after being encapsulated with
siRNA and PTX. It seems that the negative charge of phosphate backbone
of the siRNA leads to decrease in the charge of the nanoparticles. A
previous study found that the nanoparticles with a slightly negative
surface charge and average particle sizes ranging between 100 and 150 nm
have much higher transfer efficiency than larger nanoparticles (Bala,
Hariharan, & Kumar, 2004; C. He, Hu, Yin, Tang, & Yin, 2010; Panyam &
Labhasetwar, 2003). Although nanoparticles smaller than 100 may have
higher transfection efficiency than nanoparticles larger than 100 nm but
the high nonspecific uptake of these nanoparticles could increase the
side effects on healthy tissue (Puppo et al., 2014).
The transmission electron microscopy (TEM) of the nanoparticles showed
that the NPsA/siRNA/PTX, NPsB/siRNA/PTX and NPsAB/siRNA/PTX
nanoparticles have spherical shape with uniform size distribution and
smooth surface (Fig. 5). There was no significant difference between the
morphology of the nanoparticles. The results also showed that the
average size of the nanoparticles was about 100 nm.
These results were consistent with DLS data (Fig. 4).