Synthesis of Highly Monodisperse Particles Composed of a Magnetic Core and Fluorescent Shell

Abstract

Highly monodisperse particles composed of a magnetic silica core and fluorescent polymer shell were synthesized with a combined technique of heterocoagulation and soap-free emulsion polymerization. Prior to heterocoagulation, monodisperse, submicrometer-sized silica particles were prepared with the Stober method, and magnetic nanoparticles were prepared with a modified Massart method in which a cationic silane coupling agent of N-trimethoxysilylpropyl- N, N, N-trimethylammonium chloride was added just after coprecipitation of Fe (2+) and Fe (3+). The silica particles with negative surface potential were heterocoagulated with the magnetic nanoparticles with positive surface potential. The magnetic silica particles obtained with the heterocoagulation were treated with sodium silicate to modify their surfaces with silica. In the formation of a fluorescent polymer shell onto the silica-coated magnetic silica cores, an amphoteric initiator of 2,2'-azobis[ N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057) was used to control the colloidal stability of the magnetic cores during the polymer coating. The polymerization of St in the presence of a hydrophobic fluorophore of pyrene could coat the cores with fluorescent polymer shells, resulting in monodisperse particles with a magnetic silica core and fluorescent polymer shell. Measurements of zeta potential for the composite particles in different pH values indicated that the composite particles had an amphoteric property originating from VA-057 initiator.

One-Pot Reaction and Subsequent Annealing to Synthesis Hollow Spherical Magnetite and Maghemite Nanocages

“…This magnetic hysteresis phenomenon is also in agreement with previous reports by other groups [24-26]. The result reveals that these large nanocages are superparamagnetic is owing to the fact that they are composed of many small nanoparticles that show oriented aggregation into a hollow structure [27]. The saturation magnetization ( M S ) of Fe 3 O 4 nanocages was found to be 87 emu g −1 at 300 K and the M S of γ-Fe 2 O 3 nanocages was found to be 27 emu g −1 at 300 K. It is noteworthy that the M S of Fe 3 O 4 nanocages is close to that of bulk magnetite (92 emu g −1 ) [28].…”

Multimodality Imaging Probes: Design and Challenges

“…Polyacrylic acid has been polymerized around iron oxide cores with hydrophobic NIR dyes encapsulated in the hydrophobic pockets of the polymer coating 187. Pyrene has been introduced in polymer shells around IO by introducing it during the polymerization step from 3-methacryoxypropyltrimethoxysilane precursors 182. And quantum dots have been introduced to polymer shells around IOs by interspersing QD coatings (assembled through electrostatic interactions) with poly(acrylic acid) and chitosan layers 188…”

Well-Dispersed Fe3O4/SiO2 Nanoparticles Synthesized by a Mechanical Stirring and Ultrasonication Assisted Stöber Method

“…The decrease in the saturation magnetization is due to the decrease in the Bohr magnetron per unit mass caused by the increase in the thickness of silica shell. Compared with data in the references [10,11,[14][15][16][17], the maximum saturation magnetization of 21.9 emu/g (see curve c) of Fe 3 O 4 /SiO 2 NPs is relative large, which can meet most magnetic requirements in biomedical application easily. In addition, the microstructure (see Fig.…”