Functionalized silicon quantum dots tailored for targeted siRNA delivery

For RNA interference (RNAi) mediated silencing of the ABCB1 gene in Caco-2 cells biocompatible luminescent silicon quantum dots (SiQDs) were developed to serve as self-tracking transfection tool for ABCB1 siRNA. While the 2–3 nm sized SiQD core exhibits green luminescence, the QD surfaces are completely saturated with covalently linked 2-vinylpyridine that may electrostatically bind siRNA. For down-regulating P-glycoprotein (Pgp) expression of the ABCB1 gene the SiQDs were complexed with siRNA. The cellular uptake and allocation of SiQD–siRNA complexes in Caco-2 cells were monitored using confocal laser scanning microscopy and transmission electron microscopy. The release of siRNA to the cytoplasm was verified through real-time PCR quantification of the reduced ABCB1 mRNA level. Additional evidence was obtained from time-resolved in situ fluorescence spectroscopic monitoring of the Pgp efflux dynamics in transfected Caco-2 cells which yielded significantly reduced transporter efficiencies for the Pgp substrate Rhodamine 123.