We report on the suitability of core/shell nanoparticles (NPs) for magnetic fluid hyperthermia in a selfregulated and theranostic approach. Aqueous magnetic colloids based on core/shell ZnxMnyFezO4@γ-Fe2O3 and ZnxCoyFe-zO4@γ-Fe2O3 NPs were produced by a three-step chemical synthesis. Systematic deviations from stoichiometry was observed with increasing Zn substitution for both series of samples. We investigated how the chemical composition affects saturation magnetization, magnetic anisotropy and thermomagnetic properties of these core/shell NPs. The heating efficiency through specific power absorption (SPA) was analyzed in the framework of the linear response theory. SPA values obtained for NPs presenting different contrast of anisotropy between the core and shell materials indicate no evidence of enhanced exchange coupling contribution to the heating efficiency.
The heat produced by magnetic nanoparticles,
when they are submitted
to a time-varying magnetic field, has been used in many auspicious
biotechnological applications. In the search for better performance
in terms of the specific power absorption (SPA) index, researchers
have studied the influence of the chemical composition, size and dispersion,
shape, and exchange stiffness in morphochemical structures. Monodisperse
assemblies of magnetic nanoparticles have been produced using elaborate
synthetic procedures, where the product is generally dispersed in
organic solvents. However, the colloidal stability of these rough
dispersions has not received much attention in these studies, hampering
experimental determination of the SPA. To investigate the influence
of colloidal stability on the heating response of ferrofluids, we
produced bimagnetic core@shell NPs chemically composed of a ZnMn mixed
ferrite core covered by a maghemite shell. Aqueous ferrofluids were
prepared with these samples using the electric double layer (EDL)
as a strategy to maintain colloidal stability. By starting from a
proper sample, ultrastable concentrated ferrofluids were achieved
by both tuning the ion/counterion ratio and controlling the water
content. As the colloidal stability mainly depends on the ion configuration
on the surface of the magnetic nanoparticles, different levels of
nanoparticle clustering are achieved by changing the ionic force and
pH of the medium. Thus, the samples were submitted to two procedures
of EDL destabilization, which involved dilution with an alkaline solution
and a neutral pH viscous medium. The SPA results of all prepared ferrofluid
samples show a reduction of up to half the efficiency of the standard
sample when the ferrofluids are in a neutral pH or concentrated regime.
Such results are explained in terms of magnetic dipolar interactions.
Our results point to the importance of ferrofluid colloidal stability
in a more reliable experimental determination of the NP heat generation
performance.
The present survey reports on the colloidal stability of aqueous dispersions of nitrogen-rich carbon nanodots (N-CDs). The N-CDs were synthesized by thermally induced decomposition of organic precursors and present an inner core constituted of a β - C 3 N 4 crystalline structure surrounded by a surface shell containing a variety of polar functional groups. N-CDs size and structure were checked by combined analysis of XRD (X-ray Diffraction) and TEM (Transmission Electron Microscopy) measurements. FTIR (Fourier-Transform Infrared Spectroscopy) experiments revealed the presence of carboxyl and amide groups on N-CDs surface. Towards a better understanding of the relation between colloidal stability and surface charge development, zetametry experiments were applied in N-CDs dispersions at different pHs and constant ionic strength. The increase of the absolute values of zeta potential with the alkalinization of the dispersion medium is consistent with the deprotonation of carboxyl groups on N-CDs surface, which agrees with the macroscopic visual observations of long-term colloidal stability at pH 12. The saturation value of N-CDs surface charge density was evaluated by means of potentiometric-conductometric titrations. The difference between carboxyl-related surface charge and the one determined by zeta potential measurements point to the presence of oxidized nitrogen functionalities onto the N-CDs surface in addition to carboxyl groups. These novel results shed light on the electrostatic repulsion mechanism that allows for the remarkable colloidal stability of N-CDs dispersions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.