Abstract
Superparamagnetic nanoparticles (iron oxide nanoparticles—IONs) are suitable for hyperthermia after irradiating with radiofrequency radiation. Concerning the suitability for laser ablation, IONs present a low molar absorption coefficient in the near-infrared region close to 800 nm. For this reason, they are combined with other photothermal agents into a hybrid composite. Here, we show that IONs absorb and convert into heat the infrared radiation characteristic of the so-called second-biological window (1000–1350 nm) and, in consequence, they can be used for thermal ablation in such wavelengths. To the known excellent water solubility, colloidal stability and biocompatibility exhibited by IONs, an outstanding photothermal performance must be added. For instance, a temperature increase of 36 °C was obtained after irradiating at 8.7 W cm−2 for 10 min a suspension of IONs at iron concentration of 255 mg L−1. The photothermal conversion efficiency was ~72%. Furthermore, IONs showed high thermogenic stability during the whole process of heating/cooling. To sum up, while the use of IONs in the first bio-window (700–950 nm) presents some concerns, they appear to be good photothermal agents in the second biological window.
Highlights
Thermal therapy encompasses all therapeutic treatments based on conduction of heat into or out of a part of or the whole body [1]
iron oxide nanoparticles (IONs) can be degraded in vivo, where iron homeostasis is assumed by the iron-storage protein, ferritin [17,18]
IONs were synthesized by coprecipitation of iron salts in the presence of polyethylene glycol (PEG)
Summary
Thermal therapy encompasses all therapeutic treatments based on conduction of heat into or out of a part of or the whole body [1]. In photothermal ablation induced by laser, the cancer treatment provided does relatively little damage to surrounding healthy tissues because the thermal effect is solely produced when NIR light is applied and only in the presence of a PA which transforms absorbed light into heat. It is important to remark that an outer coating of maghemite may develop at the particle–water interface during magnetite oxidation [22] In this case, the non-stoichiometric structure of maghemite results in a loss of optical absorption in the NIR wavelengths regions [21]. Concerning the suitability for PTT, IONs possesses a low molar absorption coefficient in the NIR region, and an apparent poor photothermal efficacy For this motive, usually they are associated with other PA forming a hybrid nanocomposite, especially with gold or with an organic compound [14].
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