Nanopartículas contendo iões lantanídeos para termometria de luminescência

Doutoramento em FísicaA temperatura é uma variável chave que afeta a maior parte dos sistemas, quer naturais quer construídos pelo Homem. A medida da temperatura é global, uma vez que regula a cinética e a reatividade daqueles sistemas, ao nível atómico e macroscópico. Os sensores convencionais são ineficientes para a medição remota da temperatura à micro e à nanoescala o que, nos últimos anos, tem inspirado o desenvolvimento de nanotermómetros não-invasivos, sem contato, autorreferenciados e exibindo alta sensibilidade térmica. Neste contexto, a utilização de iões lantanídeos trivalentes (Ln3+), devido às suas propriedades fotoluminescentes que dependem fortemente da temperatura, tem sido uma das aproximações mais promissoras. Esta tese discuta as propriedades de nanopartículas dopadas com iões Ln3+ emitindo na gama espectral do visível e infravermelho-próximo como sensores de temperatura molecular. Na primeira parte da tese, estudaram-se nanopartículas de Gd2O3 dopadas com Nd3+ operando na gama espectral do infravermelho-próximo como nanotermómetros luminescentes baseados num rácio de intensidades. A emissão de nanotubos e nanobastonetes de Gd2O3:Nd3+ foi medida usando um tubo fotomultiplicador R928 comum na primeira janela biológica (800920 nm) tendo-se obtido na faixa fisiológica (288323 K), respetivamente, uma sensibilidade térmica e uma incerteza em temperatura de 1.75±0.04 %K-1 e 0.14±0.05 K. A dependência com a temperatura da emissão de nanoesferas de Gd2O3:Nd3+ na segunda janela biológica (12501550 nm), com excitação a 808 nm na primeira janela biológica, foi, também, estudada mostrando uma sensibilidade térmica máxima de 0.237±0.03 %K-1 a 303 K. Na segunda parte da tese foram desenvolvidas nanopartículas conversoras ascendentes de energia de Gd2O3 e SrF2 dopadas com Yb3+/Er3+ para termometria, tendo como parâmetro termométrico a intensidade integrada das transições 2H11/24I15/2/4S3/24I15/2 do ião Er3+. Desenvolveram-se nanoplataformas combinando nanotermómetros de Gd2O3:Yb3+/Er3+ com nanopartículas de Ouro (nanoaquecedores) para medir a temperatura induzida pelo plasmão das partículas metálicas. A condição ótima para um aquecimento térmico efetivo foi conseguida ajustando a banda de ressonância de superfície localizada do plasmão (LSPR) na gama fisiológica (302330 K). Quando comparadas com as nanopartículas de Gd2O3:Yb3+/Er3+, as nanopartículas de SrF2:Yb3+/Er3+ apresentam uma eficiência de emissão da conversão ascendente de energia e uma dispersibilidade superiores tendo sido estudada a dependência com a temperatura das suas propriedades de emissão, tanto em forma de suspensão como em pó. Além disso, realizaram-se medições do fluxo espectral e do rendimento quântico absoluto de emissão usando um espectrômetro com uma esfera de integração e um medidor de potência. Foi, também, proposto um método inovador para prever a curva de calibração da intensidade de emissão versus temperatura de qualquer termómetro luminescente baseado em dois níveis eletrónicos termicamente acoplados, utilizando como exemplo nanopartículas de SrF2:Yb3+/Er3+.Temperature is a master variable that affects essentially most of the natural and engineered systems. The measurement of temperature is a virtually ubiquitous requirement as it governs the kinetics and reactivity of these systems from their atomic to macroscopic level. The conventional temperature sensors, proved to be ineffective for remote temperature measurement at the micro and nanoscale. This has been strongly stimulated for the development of non-invasive, noncontact and self-referencing nanothermometers exhibiting high thermal sensitivity. In this context one of the most promising approaches proposes the use of trivalent lanthanide ions (Ln3+) that present photoluminescent properties that are temperature dependent. This thesis reports Ln3+-doped visible emitting upconverting and near-infrared emitting downshifting nanoparticles as molecular temperature sensors. Primarily, Nd3+-doped near-infrared exciting and near-infrared emitting downshifting Gd2O3 nanoparticles as an intensity-based ratiometric nanothermometer were evaluated. The performance of Gd2O3:Nd3+ nanorods were enquired using a common R928 photomultiplier tube in the first transparent biological window (800–920 nm). The highest thermal sensitivity and temperature uncertainty (1.75±0.04 %K−1 and 0.14±0.05 K, respectively) were reported for Gd2O3:Nd3+ nanorods in the physiological range (288–323 K). Similarly, the performance of Gd2O3:Nd3+ nanospheres were briefly investigated for their temperature dependent emission in the second biological window (12501550 nm) upon excitation in the first biological window (at 808 nm). The Gd2O3:Nd3+ nanospheres exhibit a maximum thermal sensitivity of 0.237±0.03 %K-1 at 303 K were obtained. Secondarily, Yb3+/Er3+-doped near-infrared exciting and visible emitting upconverting Gd2O3 and SrF2 nanoparticles were developed for thermometry based on the thermometric parameter, as the integrated intensity of 2H11/2→4I15/2/4S3/2→4I15/2 Er3+ transitions. Gd2O3 nanorods as thermometers combined with Au as heater nanoplatforms were constructed, to measure plasmon-induced temperature increase of Au nanorods. The optimal condition for the effective thermal heating was achieved by tuning the localized surface plasmon resonance band in the physiological range (302–330 K). In order to increase upconversion emission efficiency and the dispersibility, further SrF2 nanoparticles were explored and the thermal sensing properties were exploited both in powder and water suspension forms. Moreover, the measurements of spectral flux and the absolute quantum yield were accomplished followed a method using an integrating sphere-based spectrometer and a power meter. Considered a furtherance step is to demonstrate a straightforward method to predict the temperature calibration curve of any upconverting thermometer based on two thermally-coupled electronic levels independently of the medium, taking SrF2 nanoparticles as an illustrative example

The Intersection of CMOS Microsystems and Upconversion Nanoparticles for Luminescence Bioimaging and Bioassays

Organic fluorophores and quantum dots are ubiquitous as contrast agents for bio-imaging and as labels in bioassays to enable the detection of biological targets and processes. Upconversion nanoparticles (UCNPs) offer a different set of opportunities as labels in bioassays and for bioimaging. UCNPs are excited at near-infrared (NIR) wavelengths where biological molecules are optically transparent, and their luminesce in the visible and ultraviolet (UV) wavelength range is suitable for detection using complementary metal-oxide-semiconductor (CMOS) technology. These nanoparticles provide multiple sharp emission bands, long lifetimes, tunable emission, high photostability, and low cytotoxicity, which render them particularly useful for bio-imaging applications and multiplexed bioassays. This paper surveys several key concepts surrounding upconversion nanoparticles and the systems that detect and process the corresponding luminescence signals. The principle of photon upconversion, tuning of emission wavelengths, UCNP bioassays, and UCNP time-resolved techniques are described. Electronic readout systems for signal detection and processing suitable for UCNP luminescence using CMOS technology are discussed. This includes recent progress in miniaturized detectors, integrated spectral sensing, and high-precision time-domain circuits. Emphasis is placed on the physical attributes of UCNPs that map strongly to the technical features that CMOS devices excel in delivering, exploring the interoperability between the two technologies

The Intersection of CMOS Microsystems and Upconversion Nanoparticles for Luminescence Bioimaging and Bioassays

Organic fluorophores and quantum dots are ubiquitous as contrast agents for bio-imaging and as labels in bioassays to enable the detection of biological targets and processes. Upconversion nanoparticles (UCNPs) offer a different set of opportunities as labels in bioassays and for bioimaging. UCNPs are excited at near-infrared (NIR) wavelengths where biological molecules are optically transparent, and their luminesce in the visible and ultraviolet (UV) wavelength range is suitable for detection using complementary metal-oxide-semiconductor (CMOS) technology. These nanoparticles provide multiple sharp emission bands, long lifetimes, tunable emission, high photostability, and low cytotoxicity, which render them particularly useful for bio-imaging applications and multiplexed bioassays. This paper surveys several key concepts surrounding upconversion nanoparticles and the systems that detect and process the corresponding luminescence signals. The principle of photon upconversion, tuning of emission wavelengths, UCNP bioassays, and UCNP time-resolved techniques are described. Electronic readout systems for signal detection and processing suitable for UCNP luminescence using CMOS technology are discussed. This includes recent progress in miniaturized detectors, integrated spectral sensing, and high-precision time-domain circuits. Emphasis is placed on the physical attributes of UCNPs that map strongly to the technical features that CMOS devices excel in delivering, exploring the interoperability between the two technologies