Unveiling the Physicochemical Features of CoFe2O4 Nanoparticles Synthesized via a Variant Hydrothermal Method: NMR Relaxometric Properties

A series of CoFe2O4 nanoparticles were formed through a variant hydrothermal synthesis based on a self-assembled oil–water system in autoclaves at 200 °C in the presence of octadecylamine and the trivalent iron and cobalt acetylacetonates. The variation of the water content, the different valence of the cobalt precursors (Co(II) and Co(III)) as well as Fe:Co precursor ratios (2:1 and 1:1) were studied. CoFe2O4 nanoparticles with a size range of 9–16 nm of high crystallinity and enhanced saturation magnetization (∼89 emu g–1) have been isolated and characterized. Raman spectroscopy provided information concerning the lattice strain, while incorporation of Co2+ at Td sites of the spinel indicated a different inversion degree (0.67–0.60) among the samples. EPR studies showed that EPR signal and spin relaxation process were size dependent and influenced by aggregation effects. CoFe2O4 nanoparticles were converted to dual agents via a reaction between the free amine groups of the organic coating and the sulfonyl group of the fluorescent dye sulforhodamine B acid chloride (SRB) and NMR relaxometric properties were measured. The relatively high transverse relaxivity values, r2 (232.0–130.3 mM–1 s–1) were attributed to nanocluster effects in aqueous suspensions with respect with the amount of SRB and encourage their potential application as versatile agents in theranostics.