Synthesis and characterization of ultra-small superparamagnetic iron oxide nanoparticles thinly coated with silica

Abstract

Ultra-small superparamagnetic iron oxide nanoparticles (SPIOs) were synthesized by co-precipitation of iron chloride salts with ammonia and then encapsulated with thin (~2nm) layers of silica. The particles have been characterized for size, diffraction pattern, surface charge, and magnetic properties. This rapid and economical synthesis has a number of industrial applications; however, the silica-coated particles have been optimized for use in medical applications as MR contrast agents, biosensors, DNA capturing, bioseparation and enzyme immobilization.

Figure 1

LaMer Diagram illustrating the time dependence of monomers to form monodisperse colloids.

Figure 2

Citrate-complexed USPIO.

Figure 3

TEM using a JEOL 4000EX of synthesized (A) ~175nm silica beads embedded with USPIOs, (B) USPIOs coated with ~10nm-thick shells of silica, and (C) USPIOs coated with ~2.5nm-thick shells of silica.

Figure 4

Diffraction patterns using JEOL 4000EX of silica-coated USPIOs: (A) magnetite/maghemite core, and (B) silicon(IV) oxide outer shell.

Figure 5

Surface charge characterization of particles in water.

Figure 6

Magnetization versus applied field of USPIO and silica-coated USPIOs measured at (A) T=100K (±7 T), (B) T=100K (±0.1 T), (C) T=310.15K (±7 T), and (D) T=310.15K (±0.1 T).

Figure 7

Temperature dependence of the magnetization (ZFC & FC) of USPIO and Silica-USPIO at H=0.01T.