Stimuli-responsive protection of optically excited triplet ensembles against deactivation by molecular oxygen

How to Minimize Light-Organic Matter Interactions for All-Optical Sub-Cutaneous Temperature Sensing

Penetration and emanation of light into tissue are limited by the strong interaction of light with the tissue components, especially oxygenated hemoglobin and white adipose tissue. This limits the possibilities for all-optical minimal invasive sensing. In order to minimize the optical losses of light in and out of the tissue, only a narrow optical window between 630 and 900 nm is available. In this work, we realized for the first time all-optical temperature sensing within the narrow optical window for tissue by using the process of triplet-triplet annihilation photon energy upconversion (TTA-UC) as a sensing tool. For this, we apply the asymmetrical benzo-fused BODIPY dye as an optimal emitter and mixed palladium benzo-naphtho-porphyrins as an optimal sensitizer. The TTA-UC sensing system is excited with λ = 658 nm with an extremely low intensity of 1 mW × cm^-2 and is factual-protected for a time period longer than 100 s against oxygen-stimulated damage, allowing a stable demonstration of this T-sensing system also in an oxygen-rich environment without losing sensitivity. The sensing dyes we embed in the natural wax/natural matrix, which is intrinsically biocompatible, are approved by the FDA as food additives. The demonstrated temperature sensitivity is higher than ΔT = 200 mK placed around the physiologically relevant temperature of T = 36 °C.

Temperature Sensing in Cells Using Polymeric Upconversion Nanocapsules

Monitoring local temperature inside cells is crucial when interpreting biological activities as enhanced cellular metabolism leads to higher heat production and is commonly correlated with the presence of diseases such as cancer. In this study, we report on polymeric upconversion nanocapsules for potential use as local nanothermometers in cells by exploiting the temperature dependence of the triplet-triplet annihilation upconversion phenomenon. Nanocapsules synthesized by the miniemulsion solvent evaporation technique are composed of a polymer shell and a liquid core of rice bran oil, hosting triplet-triplet annihilation upconversion active dyes as sensitizer and emitter molecules. The sensitivity of the triplet-triplet annihilation upconversion to the local oxygen concentration was overcome by the oxygen reduction ability of the rice bran oil core. The triplet-triplet annihilation upconversion process could thus successfully be applied at different levels of oxygen presence including at ambient conditions. Using this method, the local temperature within a range of 22 to 40 °C could be determined when the upconversion nanocapsules were taken up by HeLa cells with good cellular viability. Thus, the higher cell temperatures where the cells show enhanced metabolic activity led to a significant increase in the delayed fluorescence spectrum of the upconversion nanocapsules. These findings are promising for further development of novel treatment and diagnostic tools in medicine.

Photo-writing self-erasable phosphorescent images using poly(N-vinyl-2-pyrrolidone) as a photochemically deoxygenating matrix

Light and oxygen dancing the rhumba: phosphorescent images could be written in PVP by photo-activation and be competitively erased by diffusional oxygen quenching.

Efficient photon upconversion at remarkably low annihilator concentrations in a liquid polymer matrix: when less is more

A triplet–triplet annihilation upconversion of 24.5% was achieved at a remarkably low 600 μM annihilator concentration in a viscous polymer matrix.

Photochemically deoxygenating solvents for triplet–triplet annihilation photon upconversion operating in air

The solvent is the solution: sulfoxides and cyclic ureas are self-deoxygenating solvents in which efficient TTA-UC can operate in air, as predicted by photo-activated phosphorescence.