Surfactant-Modified Ultrafine Gold Nanoparticles with Magnetic Responsiveness for Reversible Convergence and Release of Biomacromolecules.

It is difficult to synthesize magnetic gold nanoparticles (AuNPs) with ultrafine sizes (<2 nm) based on a conventional method via coating AuNPs using magnetic particles, compounds, or ions. Here, magnetic cationic surfactants C16H33N+(CH3)3[CeCl3Br]- (CTACe) and C16H33N+(CH3)3[GdCl3Br]- (CTAGd) are prepared by a one-step coordination reaction, i.e., C16H33N+(CH3)3Br- (CTABr) + CeCl3 or GdCl3 → CTACe or CTAGd. A simple strategy for fabricate ultrafine (<2 nm) magnetic gold nanoparticles (AuNPs) via surface modification with weak oxidizing paramagnetic cationic surfactants, CTACe or CTAGd, is developed. The resulting AuNPs can highly concentrate the charges of cationic surfactants on their surfaces, thereby presenting strong electrostatic interaction with negatively charged biomacromolecules, DNA, and proteins. As a consequence, they can converge DNA and proteins over 90% at a lower dosage than magnetic surfactants or existing magnetic AuNPs. The surface modification with these cationic surfactants endows AuNPs with strong magnetism, which allows them to magnetize and migrate the attached biomacromolecules with a much higher efficiency. The native conformation of DNA and proteins can be protected during the migration. Besides, the captured DNA and proteins could be released after adding sufficient inorganic salts such as at cNaBr = 50 mmol·L-1. Our results could offer new guidance for a diverse range of systems including gene delivery, DNA transfection, and protein delivery and separation.