Nanopartículas para nanotermometria: usando dupla razão entre picos para aumentar a sensibilidade térmica relativa

Abstract

The use of luminescent nanoparticles has grown a lot today, for several applications: for fluorescence bioimaging, as efficient biomarkers in tissues of small animals, as well as individual cells, including cancer cells, and as nanothermometers. Among the nanoparticles that are used for nanothermometry, those that are doped with rare earth ions such as Yb3+, Er3+, Tm3+, Ho3+ and Nd3+ stand out. But, in general, they have a low value for relative thermal sensitivity. Thus, in order to obtain an increase in the relative thermal sensitivity of nanoparticles doped with rare earth ions, we proposed here a new way to use their emissions to measure the temperature, in this case, we proposed that the emissions ratio associated with four emission peaks, taking the ratio between pairs of peaks, using a ratio of intensity that increases with temperature and another that decreases, to have a ratio between pairs of emissions. With this new approach we show theoretically, and experimentally, that the result will be the sum of the thermal sensitivities of each peak pair. To prove this proposal, we synthesized seven core-shell samples (nanocrystals), in some samples we made two shells and in others only one; they were doped with Yb3+, Tm3+, Er3+ and Nd3+ ions. The LaF3:YbTm@YbNd nanoparticle showed the highest value for the maximum relative thermal sensitivity, in this case, 4.0% K-1 at 29 °C, when compared to the other samples we synthesized. This value obtained is much higher than that found in the literature for a system coded with Yb3+ and Tm3+, reaching almost double the value reported in some cases by the literature. We also obtained a good value for the relative thermal sensitivity for the sample LaF3: YbTm@YbEr@YbNd, whose value was equal to 3.00% K-1 at 30 °C. Finally, we hope that our work can contribute to the use of ion-doped nanoparticles doped with rare-earth for use in nanothermometry.