Abstract
The incorporation of oleic acid and oleylamine, acting as organic surfactant coatings for a novel solvothermal synthesis procedure, resulted in the formation of monoclinic KLu(WO4)2 nanocrystals. The formation of this crystalline phase was confirmed structurally from X-ray powder diffraction patterns and Raman vibrational modes, and thermally by differential thermal analysis. The transmission electron microscopy images confirm the nanodimensional size (~12 nm and ~16 nm for microwave-assisted and conventional autoclave solvothermal synthesis) of the particles and no agglomeration, contrary to the traditional modified sol-gel Pechini methodology. Upon doping with holmium (III) and thulium (III) lanthanide ions, these nanocrystals can generate simultaneously photoluminescence and heat, acting as nanothermometers and as photothermal agents in the third biological window, i.e., self-assessed photothermal agents, upon excitation with 808 nm near infrared, lying in the first biological window. The emissions of these nanocrystals, regardless of the solvothermal synthetic methodology applied to synthesize them, are located at 1.45 μm, 1.8 μm and 1.96 μm, attributed to the 3H4 → 3F4 and 3F4 → 3H6 electronic transition of Tm3+ and 5I7 → 5I8 electronic transition of Ho3+, respectively. The self-assessing properties of these nanocrystals are studied as a function of their size and shape and compared to the ones prepared by the modified sol-gel Pechini methodology, revealing that the small nanocrystals obtained by the hydrothermal methods have the ability to generate heat more efficiently, but their capacity to sense temperature is not as good as that of the nanoparticles prepared by the modified sol-gel Pechnini method, revealing that the synthesis method influences the performance of these self-assessed photothermal agents. The self-assessing ability of these nanocrystals in the third biological window is proven via an ex-vivo experiment, achieving thermal knowledge and heat generation at a maximum penetration depth of 2 mm.
Highlights
Introduction iationsPhotothermal therapy, that employs light-absorbing agents to convert photoenergy into heat, achieving local hyperthermia, is regarded as a minimally invasive and highly efficient methodology for targeted cancer treatment [1,2,3,4]
We studied the effects on the products of the reduction of the reaction temperature and time in the microwave-assisted solvothermal approach, with the aim to develop a green approach for the synthesis of KLu(WO4
X-ray powder diffraction (XRPD) data reveal that the synthesized nanocrystals crystallize in the monoclinic system with the C2/c spatial group, as confirmed by the comparison with the reference pattern of KLu(WO4 )2 (JCPDS file 54-1204) [38], presented in Figure 1a for the undoped nanocrystals and in Figure S16 at the Supporting Information under Section S3 for the doped nanocrystals
Summary
Photothermal therapy, that employs light-absorbing agents to convert photoenergy into heat, achieving local hyperthermia, is regarded as a minimally invasive and highly efficient methodology for targeted cancer treatment [1,2,3,4]. Efficient photothermal agents require high light-to-heat conversion efficiency, small size, and working under excitation and generated emission wavelengths operating in the optical biological windows [4]. To these, it can be added real-time temperature feedback to monitor the treatment [4]. A high light-to-heat conversion efficiency allows performing effective hyperthermia with low laser powers and suppresses any overheating effect [4]. Small sizes of the photothermal agents guarantee successful intracellular studies and applications, and the effective excretion of the nanoparticles after the photothermal treatment, avoiding in-vivo toxicity [1,2,3,4].
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