Monitoring amyloid aggregation via a twisted intramolecular charge transfer (TICT)-based fluorescent sensor array

Imaging amyloid-beta (Aβ) aggregation is critical for understanding the pathology and aiding the pre-symptomatic intervention of Alzheimer's disease (AD). Amyloid aggregation consists of multiple phases with increasing viscosities and demands probes with broad dynamic ranges and gradient sensitivities for continuous monitoring. Yet, existing probes designed based on the twisted intramolecular charge transfer (TICT) mechanism mainly focused on donor engineering, limiting the sensitivities and/or dynamic ranges of these fluorophores to a narrow window. Herein, using quantum chemical calculations, we investigated multiple factors affecting the TICT process of fluorophores. It includes the conjugation length, the net charge of the fluorophore scaffold, the donor strength, and the geometric pre-twisting. We have established an integrative framework for tuning TICT tendencies. Based on this framework, a platter of hemicyanines with varied sensitivities and dynamic ranges is synthesized, forming a sensor array and enabling the observation of various stages of Aβ aggregations. This approach will significantly facilitate the development of TICT-based fluorescent probes with tailored environmental sensitivities for numerous applications.