Flame-Sprayed Superparamagnetic Bare and Silica-Coated Maghemite Nanoparticles:  Synthesis, Characterization, and Protein Adsorption−Desorption

Abstract

Superparamagnetic maghemite (γ-Fe 2 O 3 ) nanoparticles of tunable diameters and silica-coated maghemite (SiO 2 /γ-Fe 2 O 3 ) nanoparticles of controllable morphology were successfully synthesized using a one-step flame spray pyrolysis (FSP) technique. The physical, chemical, and magnetic properties of γ-Fe 2 O 3 and SiO 2 /γ-Fe 2 O 3 nanostructures were characterized and compared with those of silica-coated FSP γ-Fe 2 O 3 produced by a conventional sol-gel method. Bovine serum albumin (BSA) adsorption-desorption was investigated as a model to demonstrate the feasibility of synthesized superparamagnetic nanoparticles for bioadsorption and bioseparation. Protein adsorption was observed to follow the Langmuir isotherm, with the highest binding capacity of 348 mg of BSA/g of particle and a dissociation constant of 0.0159 g/L attainable for FSP γ-Fe 2 O 3 (d XRD ) 14 nm) in 10 mM formate buffer. Electrostatically governed BSA orientations were proposed for different particle-buffer systems. Shifting the pH of suspension with K 2 HPO 4 enabled effective recovery of adsorbed BSA.

Formation of Magnetic FexOy/Silica Core-Shell Particles in a One-Step Flame Aerosol Process

“…Nevertheless, the results suggest that it would be impossible to generate Fe x O y /silica core-shell nanoparticles in a one-step flame process, "one-step" as being defined earlier in the Introduction. This is consistent with the findings from previous studies (Ehrman et al 1999;Li et al 2006;McMillin et al 1996).…”

“…The core-shell particles and the non-core-shell particles appar- ently had different magnetic domain sizes, and hence different temperature-dependence of the magnetic properties (Tartaj et al 2002). The main magnetic properties of the core-shell particles and the non-core-shell nanoparticles are shown in Table 4, in comparison with magnetic properties of iron oxide silica core-shell nanoparticles generated in other aerosol processes (Li et al 2006;Teleki et al 2009). The core-shell particles in this study exhibited very soft room-temperature magnetization behaviors (low coercivity and remanence) in comparison to particles from the other studies.…”

“…In the past, aerosol methods based on flame and furnace have been used for the synthesis of iron oxide silica composite particles. For example, McMillin et al and Ehrman et al used Bunsen burner type premixed flame processes (Ehrman et al 1999;McMillin et al 1996), Li et al (2006) used a flame spray pyrolysis approach to synthesize iron silicon oxide particles. The products from these processes were nanoparticles that had non-core-shell structures.…”

Flexible, Multifunctional, Magnetically Actuated Nanocomposite Films

“…The main crystal phase of the fl ame-made [ 28 ] and directly-deposited Fe 2 O 3 nanoparticles is maghemite ( γ -Fe 2 O 3 ) with an average crystal size of about 9.4 nm and primary particle size of 9.9 nm (by N 2 adsorption, Supporting Information, Figure S1a), indicating rather monocrystalline iron oxide nanoparticles. Similar fl amemade Fe 2 O 3 nanoparticles have a log-normal particle size distribution with geometric standard deviation [ 28 ] σ g = 1.36-1.52, typical for nanoparticles grown by coagulation and sintering. [ 25 ] Such Fe 2 O 3 nanoparticles are superparamagnetic at room temperature [ 28 ] with a saturation magnetization of M s = 37 emu/g technique is fast, highly reproducible and scalable [ 26 ] that may facilitate commercialization of such nanocomposites.…”

“…Similar fl amemade Fe 2 O 3 nanoparticles have a log-normal particle size distribution with geometric standard deviation [ 28 ] σ g = 1.36-1.52, typical for nanoparticles grown by coagulation and sintering. [ 25 ] Such Fe 2 O 3 nanoparticles are superparamagnetic at room temperature [ 28 ] with a saturation magnetization of M s = 37 emu/g technique is fast, highly reproducible and scalable [ 26 ] that may facilitate commercialization of such nanocomposites.…”