Conjugation to gold nanoparticles enhances polyethylenimine's transfer of plasmid DNA into mammalian cells

TLDR

PEI2 chains of ~2 kDa were covalently linked to gold nanoparticles to evaluate their effectiveness as plasmid DNA delivery vectors into COS‑7 cells in serum-containing media. Transmission electron microscopy showed that the DNA–PEI2–GNP complexes reach the nucleus within less than one hour after transfection. The PEI2–GNP conjugate achieved a 12‑fold increase in transfection efficiency over unmodified PEI, and adding amphiphilic N‑dodecyl‑PEI2 doubled this effect, yielding a ternary complex that transfects 50 % of cells—over ten times more efficient than 25‑kDa PEI.

Abstract

Branched polyethylenimine (PEI) chains with an average molecular mass of 2 kDa (PEI2) have been covalently attached to gold nanoparticles (GNPs), and the potency of the resulting PEI2–GNPs conjugates as vectors for the delivery of plasmid DNA into monkey kidney (COS-7) cells in the presence of serum in vitro has been systematically investigated. The transfection efficiencies vary as a function of the PEI/gold molar ratio in the conjugates, with the best one (PEI2–GNPII) being 12 times more potent than the unmodified polycation. This potency can be further doubled by adding amphiphilic N -dodecyl–PEI2 during complex formation with DNA. The resulting ternary complexes are at least 1 order of magnitude more efficient than the 25-kDa PEI, one of the premier polycationic gene-delivery vectors. Importantly, although unmodified PEI2 transfects just 4% of the cells, PEI2–GNPII transfects 25%, and the PEI2–GNPII/dodecyl–PEI2 ternary complex transfects 50% of the cells. The intracellular trafficking of the DNA complexes of these vectors, monitored by transmission electron microscopy, has detected the complexes in the nucleus <1 h after transfection.