Realization of highest specific absorption rate near superparamagnetic limit of CoFe2O4 colloids for magnetic hyperthermia applications

Abstract

Magnetic nanoparticles offer some attractive possibilities in biomedicine with local heat generation abilities. Here we report on the realization of highest specific absorption rate (∼2 kW g−1) and a stable dynamic heat production (42–46 °C) using oleic acid coated CoFe2O4 based ferrofluids which are very promising for hyperthermia applications. CoFe2O4 nanoparticles with different sizes were prepared via co-precipitation method followed by heat treatment in the temperature range 100–600 °C to vary the particle sizes from 12–24 nm. Structural analysis using high resolution transmission electron microscopy (HRTEM) shows well separated oleic acid coated CoFe2O4 nanoparticles with a tapered spherical nature and narrow size (3 nm) distribution. Thermo-gravimetric analysis reveals the strong bonding of oleic acid to the CoFe2O4 nanoparticles. Magnetization studies show oleic acid coated CoFe2O4 nanoparticles have high saturation magnetization and reduced surface spin randomization compared to bare particles. Heat production efficiency was studied near the superparamagnetic limit of CoFe2O4 as a function of magnetic core size and ferrofluid concentration. For a given particle size and concentration, the maximum specific absorption rate varies as the square of the magnetic field applied. Notable increase in the maximum specific absorption rate was found with decrease in particle size and concentration. MTT assay studies with L-929 cells using oleic acid coated CoFe2O4 nanoparticles reveals that the particles with a size of 12 nm are more biocompatible compared to particles with a size of 24 nm.