Poly-L-Lysine coated fluorescent upconversion nanoparticles for siRNA delivery and tracking

Abstract

ABSTRACTNanoparticle-based vectors are fast becoming the main choice for nucleic acid delivery. Fluorescent nanoparticles have the added advantage of tracking the delivery process and also of tracking cells transfected with nucleic acids for cell therapy. Fluorescent upconversion nanoparticles (UCNs) are ideal candidates for tracking since they are excited by NIR light and hence have very low phototoxicity, high signal-to-noise ratio and enable imaging in deep tissues. UCNs coated with a layer of silica and adsorbed with siRNA or siRNA loaded into the mesoporous silica coating on the UCNs have been used for siRNA delivery. However the loading of siRNA is very poor since the silica coating is negatively charged and it repels the negatively charged siRNA limiting the amount of siRNA that can be adsorbed on the surface of nanoparticles. Here we report the use of a layer-by-layer approach to coat the UCNs with Poly-L-Lysine (PLL) and use it for delivery. Highly monodispersed UCNs were synthesized with an average size of 50 nm. They were then modified with PLL and STAT-3 siRNA was adsorbed on to the surface of the modified UCNs. The loading of the siRNA was found to be 60 % more efficient by this approach as compared to silica coated UCNs alone. The PLL-coated UCNs also were minimally cytotoxic as shown by MTS assay. The siRNA coated UCNs also efficiently transfected B16F0 cells and knocked down STAT3 significantly and also enabled cell imaging. Thus, This method shows good promise for siRNA delivery and tracking and this could also be extended to in-vivo transfection and tracking.