Stability and Relaxation Mechanisms of Citric Acid Coated Magnetite Nanoparticles for Magnetic Hyperthermia

DE SOUSA,M.ELISA; M. B. FERNÁNDEZ VAN RAAP; P. C. RIVAS; P. MENDOZA ZÉLIS; P. GIRARDIN; PASQUEVICH, GUSTAVO; JOSE L. ALESSANDRINI; DIEGO MURACA; FRANCISCO H. SANCHEZ

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Lugar: Washington; Año: 2013 p. 5436 - 5445

1932-7447

Magnetite (Fe3O4) nanoparticles are proper materialsfor Magnetic Fluid Hyperthermia applications whenever theseconjugate stability at physiological (neutral pH) medium and highspecific dissipation power. Here, magnetite nanoparticles 9−12 nmin size, electrostatically stabilized by citric acid coating, withhydrodynamic sizes in the range 17−30 nm, and well dispersed inaqueous solution were prepared using a chemical route. Theinfluence of media acidity during the adsorption of citric acid (CA)on the suspension?s long-term stability was systematicallyinvestigated. The highest content of nanoparticles in a stable suspension at neutral pH is obtained for coating performed atpH = 4.58, corresponding to the larger amount of CA molecules adsorbed by one carboxylate link. Specific absorption rates(SARs) of various magnetite colloids, determined calorimetrically at a radio frequency field of 265 kHz and field amplitude of40.1 kA/m, are analyzed in terms of structural and magnetic colloid properties. Larger dipolar interactions lead to larger Néelrelaxation times, in some cases larger than Brown relaxation times, which in the present case enhanced magnetic radio frequencyheating. The improvement of suspension stability results in a decrease of SAR values, and this decrease is even large incomparison with uncoated magnetite nanoparticles. This fact is related to interactions between particles.