Correlation of phase composition, magnetic properties and hyperthermia efficiency of silica-coated FeCo nanoparticles for therapeutic applications

Abstract

The local atomic order, magnetic properties, hyperthermia efficiency, drug loading capacity and in-vitro cytotoxicity are investigated for the core–shell (Fe25Co75)x(SiO2)100-x (70 ≤ x ≤ 100, wt.%) nanoparticles (NPs) sintered by the metals co-precipitation followed with SiO2 TEOS deposition. Electron microscopy reveal the formation of nearly spherical structures with medium diameter from 80 nm to 220 nm containing 20–50 nm cores identified by XRD as α-FeCo bcc alloy. Mössbauer spectra and magnetometry reflects the formation of magnetically-interacting net of single-domain FeCo cores with broad size distribution. Observed decrease in magnetization (MS) and effective magnetic anisotropy (Keff) for NPs with × is the consequence of the increasing thickness of the SiO2 shells. Calculations indicate that there is an optimal thickness δ of SiO2 shells ranging between 90 ÷ 120 nm for the highest value of specific absorption rate (SAR) originating from their effect on Keff values. Experimentally proved that SAR has the highest value for (FeCo)80(SiO2)20 NPs in correlation with the Linear Response Theory approach. High drug loading capacity (up to 98%) and low in-vitro cytotoxicity (IC50 index below 230 µg/ml) experimentally proved for (FeCo)x(SiO2)100-x NPs make them perfect candidates for designing smart drug delivery systems.