All‐Optical Temperature Sensing in Organogel Matrices via Annihilation Upconversion

Abstract

Modified organogels are bicontinuous colloidal systems which form a three-dimensional network embedding well-solvated organic dyes sensitive to minor changes in its microenvironment. It was demonstrated that these natural wax/oils based organogels can be applied for minimally invasive temperature sensing in life-science objects. The desired temperature sensitivity of better than 100 mK, centered around the physiologically relevant temperature of 36°C, is warranted by using the process of triplet-triplet annihilation photon energy upconver-sion (TTA-UC) as a sensing mechanism. This all-optical sensing technique, based on ratiometric-type signal registration, ensures significant independence of the data obtained on excitation intensity instabilities, local molecular concentration fluctuations and field-of-view variations. The TTA-UC system is effectively protected for more than 1000 s against oxygeninduced damage, allowing stable performance of this temperature-sensing system even in ambient environments without lost of sensitivity and applying the same calibration curve.

Stimuli‐Responsive Molecular Photon Upconversion

“…Theratiometric temperature sensing can be also achieved based on the intensity ratio between the residual sensitizer phosphorescence (rSPh) and the delayed emitter fluorescence (dEF), according to areport by Landfester,Baluschev et al [55] In natural-wax-oil-based organogels,t he TTA-UC system is effectively protected for more than 1000 sa gainst oxygen quenching thanks to the pronounced singlet-oxygen-scavenging properties of the natural oils.B yi ncreasing the temperature,t hat is,b yd ecreasing the viscosity of the hydrophobic matrix, the intensity of the rSPh decreases,w hile simultaneously,the intensity of the dEF increases (Figure 10 a). In the optimized sample composition, the ratio dEF/rSPh changes more than 15 times for atemperature interval of DT = 15 8 8C-45 8 8Cc entered around the temperature of interest % 36 8 8C: this allows for achieving at emperature sensitivity of up to 100 mK, optically achieved in ambient environment around life-science-relevant temperatures (Figure 10 b).…”

“…To expand the scope of TTA-UC to sensing applications,i ti sp ivotal to develop at oolbox of mechanisms to make TTA-UC responsive to avariety of external stimuli. TTA-UC emission has been successfully regulated by external stimuli including temperature, [46][47][48][49][50][51][52][53][54][55] oxygen, [56] light, [57] mechanical force, [58] electric field, [59] and chemicals. [60][61][62] However,t here has been no systematic understanding of the underlying mechanisms to switch TTA-UC.…”

Stimuli‐Responsive Molecular Photon Upconversion

“…The ratiometric temperature sensing can be also achieved based on the intensity ratio between the residual sensitizer phosphorescence (rSPh) and the delayed emitter fluorescence (dEF), according to a report by Landfester, Baluschev et al . In natural‐wax‐oil‐based organogels, the TTA‐UC system is effectively protected for more than 1000 s against oxygen quenching thanks to the pronounced singlet‐oxygen‐scavenging properties of the natural oils.…”

“…To expand the scope of TTA‐UC to sensing applications, it is pivotal to develop a toolbox of mechanisms to make TTA‐UC responsive to a variety of external stimuli. TTA‐UC emission has been successfully regulated by external stimuli including temperature, oxygen, light, mechanical force, electric field, and chemicals . However, there has been no systematic understanding of the underlying mechanisms to switch TTA‐UC.…”

Thermally activated delayed fluorescence in an optically accessed soft matter environment

“…For instance, for a temperature interval of nearly DT B 40 K, the Q. Y. of the delayed fluorescence signal is increased more than 400%. [64][65][66] Simultaneously, the energy gap between S 1 and T 1 levels of the fluorescent organic molecule is substantially larger, for instance DE ST B 0.8-1.2 eV. [18][19][20][21][22][23][24][25]…”