Modifying the Surface Properties of Superparamagnetic Iron Oxide Nanoparticles through A Sol−Gel Approach

TLDR

Multifunctional superparamagnetic iron oxide nanoparticles can be magnetically manipulated and optically characterized, enabling diverse applications. The study develops a sol‑gel method to coat superparamagnetic iron oxide nanoparticles with uniform amorphous silica shells. By varying sol‑gel precursor concentration, the silica shell thickness (2–100 nm) is tuned, and fluorescent dyes are covalently incorporated into the shells during the sol‑gel process. The method successfully coated both commercial ferrofluid particles and lab‑synthesized nanoparticles, demonstrating its versatility.

Abstract

This paper describes a sol−gel approach for the coating of superparamagnetic iron oxide nanoparticles with uniform shells of amorphous silica. The coating process has been successfully applied to particles contained in a commercial ferrofluid (e.g., the EMG 304 of Ferrofluidics) and those synthesized through a wet chemical process. The thickness of silica coating could be conveniently controlled in the range of 2−100 nm by changing the concentration of the sol−gel solution. Fluorescent dyes, for example, 7-(dimethylamino)-4-methylcoumarin-3-isothiocyanate (DACITC) and tetramethylrhodamine-5-isothiocyanate (5-TRITC), have also been incorporated into the silica shells by covalently coupling these organic compounds with the sol−gel precursor. These multifunctional nanoparticles are potentially useful in a number of areas because they can be simultaneously manipulated with an externally applied magnetic field and characterized in situ using conventional fluorescence microscopy.