LUMINESCENT NANOTHERMOMETRY USING MULTIFUNCIONAL NaGdF4 NANOPARTICLES DOPED WITH Nd³⁺, Yb³⁺, AND Ho³⁺

In cancer treatment, thermal therapies enhance the efficacy of conventional approaches such as chemotherapy and radiotherapy. Furthermore, studies have shown that this method can activate the immune system. Among the various strategies to generate heat, photothermal therapy (PTT) stands out, wherein nanoparticles (NPs) increase local temperature by absorbing light energy in the near-infrared (NIR) range. However, non-invasive monitoring of heat delivery remains a major challenge, which can be addressed by luminescent nanothermometry (LNT), since the fluorescence intensity of specific ions and molecules can serve as a temperature-sensitive parameter. In this work, NaGdF₄-based nanoparticles doped with Nd³⁺, Yb³⁺, and Ho³⁺ were synthesized via a solvothermal process, coated with poly(acrylic acid), and dispersed in aqueous medium to form a stable suspension. LNT measurements were carried out using an 808 nm diode laser to excite Nd³⁺ ions, a thermal camera to monitor the sample surface temperature, and an optical fiber positioned at a 90° angle to the laser to collect the emitted fluorescence signal, which was analyzed using a modular spectrophotometer. The potential of the NPs as fluorescent tracers was further evaluated using a fluorescence molecular tomography (FMT) system. Additionally, magnetic resonance imaging (MRI) tests demonstrated their potential as contrast agents due to the presence of Gd in their matrix. Using a fluorimeter, upconversion emission in the visible range arising from Ho³⁺ ions in the NPs was observed. The NPs exhibited strong performance as both FMT imaging tracers and luminescent nanothermometers, conferring them a multifunctional character. The thermal sensitivity measured at 45 °C was 0.363%, indicating potential for early-stage tumor detection. Moreover, MTT tests (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) with RAW 264.7 macrophages are currently being conducted to assess NP cytotoxicity at different concentrations, as well as experiments involving varied thermal doses to evaluate cell survival rates under heat exposure.