TICT-based thiophene donor-π-acceptor fluorescent sensors for selective detection of tau and amyloid-β aggregates in cellular and brain tissues

초록

This study reports the development of thiophene-extended donor-pi-acceptor (D-pi-A) fluorescent probes exhibiting twisted intramolecular charge transfer (TICT) characteristics for the selective detection of tau and amyloid-beta (A beta) aggregates, key pathological hallmarks of Alzheimer's disease (AD). A series of derivatives (3-5) were designed by modulating the pi-conjugated bridges to control intramolecular rotational dynamics and environmental sensitivity. Solvatochromism, Lippert-Mataga, viscosity-dependent fluorescence, and density functional theory (DFT) calculations supported their environment-sensitive ICT/TICT behavior. Increasing viscosity markedly enhanced fluorescence, consistent with restricted intramolecular rotation and reduced nonradiative relaxation. In vitro binding assays revealed that aggregate selectivity is strongly dependent on pi-conjugation, with compounds 3 and 4 preferentially responding to tau aggregates, while compound 5 exhibited high selectivity for A beta aggregates. In living cells, probe 4a selectively detected tau aggregates in an aggregation-dependent manner with near-infrared emission (similar to 680 nm), whereas 5d showed strong fluorescence enhancement toward intracellular A beta aggregates. Molecular docking studies supported these findings, indicating preferential binding of 4a to tau filaments and 5d to A beta aggregates. Importantly, ex vivo studies demonstrated that 5d robustly detects A beta plaques in APP/PS1 mouse brain with high specificity and strong correlation with antibody staining, whereas 4a did not show selective detection of tau aggregates in brain tissue. These results highlight the critical role of microenvironment-dependent activation of TICT fluorophores in determining aggregate selectivity and establish thiophene-based D-pi-A probes as a promising platform for selective imaging of AD-related protein aggregates.

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