RESUMO

Proteins are involved in numerous cellular activities such as transport and catalysis. Misfolding during biosynthesis and malfunctioning as a molecular machine may lead to physiological disorders and metabolic problems. Protein folding and mechanical work may be viewed as thermodynamic energetically favorable processes in which stochastic nonequilibrium intermediate states may be present with conditions such as thermal fluctuations. In my opinion, measuring those thermal fluctuations may be a way to access the energy exchange between the protein and the physiological environment and to better understand how those nonequilibrium states may influence the misfolding/folding process and the efficiency of the molecular engine cycle. Here, I discuss luminescence thermometry as a possible way to measure those temperature fluctuations from a single-molecule experimental perspective with its current technical limitations and challenges.

Assuntos

Luminescência , Termometria , Proteínas , Temperatura , Termodinâmica

RESUMO

There is a large interest in luminescent materials for application as temperature sensors. In this scenario, we investigate the performance of neodymium-doped alkaline-earth fluoride (Nd3+ :MF2 ; M=Ba, Ca, Sr) crystalline powders prepared by combustion synthesis for optical temperature-sensing applications based on the luminescence intensity ratio (LIR) technique. We observe that the near-infrared luminescence spectral profile of Nd3+ changes with the temperature in a way that its behavior is suitable for optical thermometry operation within the first biological window. We also observe that the thermometric sensitivities of all studied samples change depending on the spectral integration range used in the LIR analysis. Nd3+ :CaF2 presents the largest sensitivity values, with a maximum absolute sensitivity of 6.5×10-3 /K at 824 K and a relative sensitivity of 1.71 %/K at human-body temperature (310 K). The performance of CaF2 for optical thermometry is superior to that of ß-NaYF4 , a standard material commonly used for optical bioimaging and temperature sensing, and on par with the most efficient oxide nanostructured materials. The use of thermometry data to help understand structural properties via Judd-Ofelt intensity standard parameters is also discussed.

Assuntos

Luminescência , Nanoestruturas , Humanos , Medições Luminescentes , Nanoestruturas/química , Pós , Temperatura

RESUMO

Quenching of photoluminescence due to optical heating generated by high power laser sources has been identified as a major concern for photonics applications that relies on inorganic phosphor materials. Here we investigate how erbium-doped strontium fluoride (Er3+:SrF2) powders prepared by combustion synthesis respond to intense optical heating. We found that the near-infrared to visible photon up-conversion (UC) luminescence from Er3+ was quenched and the internal temperature of the sample increased from 298 to 695 K when the excitation power of a CW diode laser operating at 808 nm was increased from 0.1 to 2.1 W. However, when SrF2 was co-doped with Al3+, we observed an increase in the UC intensity and an unexpected internal temperature reduction of up to 155 K for an excitation power of 2.1 W. Our analysis suggests that Al3+ decreases the phonon energy and increases the local symmetry of the environment of the rare-earth ion in SrF2.

RESUMO

The effect of the presence of ytterbium (Yb3+) on the near-infrared (NIR) emission profile of erbium (Er3+), more specifically the 4I13/2 â†’ 4I15/2 radiative transition around 1.5 µm, in yttrium silicate crystalline ceramic powders prepared by combustion synthesis was investigated under different NIR laser excitation wavelengths (λ = 808 and 975 nm). Enhancement of fluorescence around 1.5 µm due to the presence of Yb3+ was observed, which has potential use in medicine (NIR-III biological window) and optical communications (C-band transmission window). Two different excitation channels involving energy transfer between Er3+ and Yb3+ were studied: one involving the sensitization of Er3+ by Yb3+ (for λ = 975 nm laser light excitation) and the other involving direct excitation of Er3+ with Yb3+ acting as an energy reservoir (for λ = 808 nm laser light excitation). The energy transfer mechanisms of both processes are discussed in the text.

RESUMO

Er(3+) doped nanocrystalline powders are extensively used for thermometry based on luminescence spectral analysis. The luminescence from Er(3+) is produced by a nonlinear (two-photon) absorption process which may generate strong internal heat by activation of nonradiative relaxation channels. If the heat dissipation is not efficient, as is the case for compact powders, there will be inaccurate readings of the temperature. Our proposed solution is to cool down Er(3+) by transferring part of its accumulated energy to another rare-earth element in the lattice. Here, we show our results for Er(3+)-Tm(3+) co-doped yttrium silicate powders prepared by combustion synthesis.

RESUMO

Here, we report the role of crystallite size and surrounding medium on the upconversion emission of Er3+ in BaTiO3 oxide nanocrystals. The samples were prepared by sol-emulsion-gel method and heat-treated at two different temperatures yielding powders containing nanoparticles of different sizes. Green (550 nm) and red (660 nm) upconversion emission were observed at room temperature from the 4S3/2 and 4F9/2 levels of BaTiO3:Er3+ nanocrystals. The pump power dependence study confirms that all these upconversion emission lines are a two-photon absorption process. We observed that the luminescence lifetime is shorter for the sample containing smaller particles. Optical thermometry experiments were performed in air, water and glycerol in a temperature range from 27.1 up to 47.1 degrees C aiming to use this material as a biological temperature sensor.

RESUMO

We investigated the frequency upconversion (UC) process in BaTiO3:Er3+ nanocrystals for excitation wavelengths in the range 638 to 660 nm. Green upconversion emissions at 526 and 547 nm corresponding to 2H11/2 --> 4I15/2 and 4S3/2 --> 4I15/2 to transitions of the Er3+ were observed. The excitation spectrum for UC emissions presented three bands, due to ground state and excited state absorption of Er3+ ions. The UC intensity as a function of the laser power was investigated and it was found this a two-photon absorption process.