Nanopartículas luminescentes para sensoriamentos na região do SWIR

Abstract

Research on luminescent nanothermometers (LNTs) is constantly growing due to the need to read and control the temperature of various physiological processes that occur, among others, in biological systems such as tissues, cells and living organisms, enabling the diagnosis and treatment of diseases. In this sense, nanoparticles (NPs) doped with rare earths ions have stood out for presenting several advantages such as having a wide spectral range from ultraviolet to infrared. Thus, they have luminescent properties within the three biological windows (BWs), which are regions where autofluorescence, dispersion and absorption of light by biological tissues are minimized, allowing less influence of the environment under study. In this thesis, we explore emissions and excitations within the BWs, as both are extremely important. The main focus of our study was the short-wave infrared (SWIR) emissions/excitation, which basically operates from 0.7 to 2.5 µm, mainly within the BW-II (1, 0 - 1.35 µm) and BW-III (1.5 - 1.9 µm). However, in an early part of our work, which focused on the effects of core-shell structure engineering, we explored emissions at BW-I (0.65 – 0.94 µm) under excitation at the minimum of the BW-I. In this part we demonstrate that the core-shell engineering, which allows the spatial separation of the emitting elements and, therefore, a control of the energy transfer processes between ions and ions to defects, has a very important role to maintain the spectral form of the NPs emissions in the presence of biological material. Despite the promising applications of LNTs, concerns have arisen about their reliability due to tissue-induced spectral distortions that are present even in BW-II that have been heavily exploited recently. We present an innovative solution to this problem, demonstrating the effectiveness of shifting the operating range of these LNTs to BW-III. Through experimental evidence using CaF2 NPs tri-doped with ytterbium, erbium and thulium, we demonstrate that the luminescence spectra acquired in BW-III are minimally distorted by the presence of tissue, paving the way for reliable LNTs. In addition, advanced analysis (Multiple Linear Regression) of the emission spectra allows obtaining subdegree thermal uncertainties. Aware of the strong absorption of water in the spectral region between BWs II and III (1.4 and 1.5 µm), we explored single-doped LaF3 NPs with Tm3+ as a potential humidity sensor through the use of emissions at 1230 (in JB -II) and 1470 nm. The results showed a reduction greater than 97% in the emission intensity at 1470 nm with the presence of a 2 mm water film, resulting in a relative sensitivity between 0.083 – 0.125 %µm-1 for the smallest water films, demonstrating to be a potential luminescent humidity sensor. Experiments are underway for a comparative study with commercial and other humidity sensors.