Fe₃O₄@SiO₂ Nanoparticles Functionalized with Gold and Poly(vinylpyrrolidone) for Bio-Separation and Sensing Applications

Large Fe3O4@SiO2 nanoparticles (∼200 nm) functionalized with gold and poly(vinylpyrrolidone) have been synthesized, characterized, and evaluated for bioseparation and sensing applications. The particles have been characterized using a combination of experimental techniques including ultraviolet visible spectroscopy, energy-dispersive spectroscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, electron microscopy, superconducting quantum interference device magnetrometry, and surface-enhanced Raman sensing (SERS) spectroscopy. The particles have a unique surface morphology comprised of roughened gold nodules. The surface coatings prevent oxidation and render the particles easy to functionalize in order to target a wide range of moieties. The gold coverage is not only uniform across the entire particle surface but also ultrathin so as to maintain a high percentage of the cores magnetic saturation (∼68%) when compared to that of bare magnetite. The gold nodules facilitate the generation of hot spots that enhance the electromagnetic field associated with the particle surface and are therefore useful in sensing applications like SERS, and the strong magnetic core allows for rapid separation (∼30 s) of target molecules from solution once they are bound to the particles.