Tetrahydroxyquinone: A Suitable Coating for Ferrofluids Used in Magnetic Hyperthermia

Abstract

In this work, tetrahydroxyquinone (THQ) was used for the first time to coat iron oxide nanoparticles (IONPs) and to carry out in vitro experiments in magnetic hyperthermia. Synthesis by co-precipitation resulted in spherical IONPs with a core diameter of 13 ± 3 nm and covered by a 0.5 nm thick coat of THQ, which provided them with a reasonably good zeta potential of ζ = −28 ± 2 mV at pH = 7.3, and thus colloidal stability. The magnetic properties of the THQ-coated IONPs are promising: the low coercive field of Hc = 7 Oe, the high magnetic saturation of Ms = 70.5 emu/g and the low blocking temperature of Tb = 273 K indicate superparamagnetic characteristics at room temperature. Additionally, a high specific absorption rate SAR = 135 W/g (at 300 Oe and 530 kHz) was determined. Cell biological experiments using the human cell line HT-29 evidenced negligible cytotoxicity up to 2 mg/mL. Magnetic hyperthermia (MHT) assays demonstrated fast and reliable heating and reduced the metabolic activity of the cells to 42% upon reaching 42 °C within 15 min. The production of ROS by THQ-coated IONPs could not be detected, which may indicate a reduction in the undesired side effects caused by oxidative stress. Considering these good physicochemical and cell biological properties, this ferrofluid is a promising candidate for the initiation of in vivo experiments for cancer treatment by MHT in murine models.

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“…This is an important property because the negative charge of the SPIONs promotes their endocytosis and, at the same time, the ferrofluid maintains colloidal stability in biological experiments, where the pH of the system has to be very close to pH = 7.4. A measurement of the polydispersity index PDI when pH ≈ 6.8 reaches PDI ≈ 0.22, which is a relatively low homogeneity (according to the size distribution of Figure 1c), but it is considered sufficient for magneto-calorimeter tests and magnetic hyperthermia applications [20,23,28,29]. The magnetic saturation of the SPIONs (red line) was 50 emu/g approximately 30% lower than the one of pure magnetite (black line) (Figure 3a).…”