Enhanced two-photon absorption and fluorescence upconversion in Thioflavin T micelle-type aggregates in glycerol/water solution

• Systematic characterization of the two-photon absorption of ThT in different mixtures of water-glycerol solution.
• Enhanced TPA of ThT in micelle-type aggregates.
• Maximum δTPA=300δTPA=300 GM at 540 nm in 8.75% glycerol/water solutions.
• Our results are expected to encourage the application of ThT as a biocompatible two-photon probe.

In this article, we report the systematic characterization of the two-photon absorption of ThT in different mixtures of glycerol/water solution. The relationships of TPA peak position and amplitude revealed a dependence on particle size suggesting that the curious trend observed in TPA with changing glycerol content can be attributed to the presence of micelle-type aggregates. Consequently, the relatively strong TPA cross-section (δTPA = 300 GM) obtained in 8.75% glycerol/water solutions could be attributed to the immobilization of dye molecules and the strong coupling of the molecular transition dipoles in micelle-type aggregates. This enhancement of TPA, in addition to the already reported significant fluorescence quantum yield of ThT attached to brain tissue, is expected to boost the application of this compound for in vitro and perhaps in vivo high resolution multiphoton bioimaging of amyloids in brain tissue.

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