Self-referencing thermometry in the nanoscale

Abstract

Na ´ultima d´ecada emergiu uma linha de investiga¸c˜ao muito activa em term´ometros n˜ao invasivos e precisos que possam determinar temperatura `a escala nanom´etrica. Esta investiga¸c˜ao foi fortemente estimulada pelas numerosas solicita¸c˜oes da nanotecnologia e da biomedicina, por exemplo. Uma das abordagens mais promissoras prop˜oe o uso de i˜oes trivalentes de lantan´ıdeos que apresenta propriedades fotoluminescentes que dependem da temperatura. Neste trabalho demonstra-se que esta t´ecnica combina as vantagens de te um limite de detec¸c˜ao de 0.5 graus com sensibilidade at´e 4.5 % · K−1. Este term´ometro molecular pode ser processado em filmes finos ou nanopart´ıculas, abrindo os campos de aplica¸c˜ao a diferentes utiliza¸c˜oes. As nanopart´ıculas de s´ılica produzidas s˜ao caracterizadas na presen¸ca e na ausˆencia de i˜oes lantan´ıdeos. Sem o metal, as nanopart´ıculas de APTES/TEOS demonstram ser luminescentes sob excita¸c˜ao UV sem necessidade de utilizar qualquer tratamento t´ermico. O rendimento quˆantico de emiss˜ao depende apenas da propor¸c˜ao dos silanos e pode atingir o valor de 0.15 ± 0.02. A co-dopagem destas nanopart´ıculas com Eu3+ e Tb3+ permite obter sondas com resposta raciom´etrica, com a possibilidade de ajustar a gama de temperaturas de opera¸c˜ao e a sensibilidade, via desenho inteligente da matriz de suporte e dos ligandos de β-dicetona que est˜ao coordenados ao i˜ao met´alico. Quando processados como filmes, este term´ometro permite o mapeamento de temperaturas com resolu¸c˜ao espacial 1.8 μm. A racionaliza¸c˜ao da dependˆencia de temperatura ´e uma ferramenta ´util para desenvolver term´ometros que operam em gamas de temperatura espec´ıficos (e.g. gama de temperatura fisiol´ogica, 290-340 K) com sensibilidade acima de 0.5 % · K−1. A combina¸c˜ao de esfor¸cos de um grande n´umero de diversas disciplinas ir´a previsivelmente permitir o surgimento de term´ometros moleculares novos e sofisticados, preenchendo os principais requisitos das nanociencias.

Non-invasive precise thermometers working at the nanoscale with high spatial resolution, where the conventional methods are ineffective, have emerged over the last decade as a very active field of research. This has been strongly stimulated by the numerous challenging requests arising from nanotechnology and biomedicine. One of the most promising approaches proposes the use of trivalent lanthanide ions that present photoluminescent properties that are temperature dependent. In this work is demonstrated that the technique possesses both the advantages of self-referencing and limit of detection above 0.5 degree with sensitivity up to 4.5 % · K−1. This molecular thermometer can be processed as thin films or nanoparticles, open the field of use to several applications. The silica nanoparticles produced are characterized in the presence and absence of the lanthanide ions. Without the metal the APTES/TEOS silica nanoparticles prove to be luminescent upon UV excitation without need of the annealing step. The emission quantum yield depends only of the silanes proportion can reach the value of 0.15 ± 0.02. Co-doping this nanoparticles with Eu3+ and Tb3+ the nanoparticles become ratiometric temperature probes with possibility of tailoring the temperature range of operation and the sensitivity, via smart design of the host matrix and the β-diketonate ligand that is coordinated to the metal ion. When processed as film, the thermometer allows temperature mapping with spatial resolution up to 1.8 μm. The rationalization of the temperature dependent emission provides useful tools to design thermometers working in specific temperature ranges (e.g. physiological temperature range, 290-340 K) with sensitivity above 0.5 % · K−1. Combining efforts from a large number different disciplines it is predictable that new and sophisticated molecular thermometers will emerge, fulfilling the major demands of the nanosciences.