Turn-on fluorescence imaging is routinely studied; however, turn-on chemiluminescence has been rarely explored for in vivo imaging. Herein, we report the design and validation of chemiluminescence probe ADLumin-1 as a turn-on probe for amyloid beta (Aβ) species. Two-photon imaging indicates that ADLumin-1 can efficiently cross the blood–brain barrier and provides excellent contrast for Aβ plaques and cerebral amyloid angiopathy. In vivo brain imaging shows that the chemiluminescence signal of ADLumin-1 from 5-month-old transgenic 5xFAD mice is 1.80-fold higher than that from the age-matched wild-type mice. Moreover, we demonstrate that it is feasible to further d ually- a mplify s ignal via c hemiluminescence r esonance e nergy t ransfer (DAS-CRET) using two non-conjugated smart probes (ADLumin-1 and CRANAD-3) in solutions, brain homogenates, and in vivo whole brain imaging. Our results show that DAS-CRET can provide a 2.25-fold margin between 5-month-old 5xFAD mice and wild type mice. We believe that our strategy could be extended to other aggregating-prone proteins.

In vivo detection of cerebral β-amyloid fibrils may facilitate the monitoring of β-amyloidosis in the brain and effectiveness of antiamyloid therapies. Thioflavin T (ThT) is a widely used dye for the spectroscopic determination of β-amyloid fibrils, but its ability to detect cerebral β-amyloid fibrils in vivo is limited due to the charged molecule. To this end, a smart dicynomethylene-4H-pyran (DCM) fluorophore, namely, (E)-2-(2-(4-(dimethylamino)styryl)-6-methyl-4H-pyran-4-ylidene) malononitrile (PAD-1), was evaluated for in vivo fluorescence imaging of cerebral β-amyloid fibrils. PAD-1 rapidly entered the brain with high initial brain uptake after intravenous injection, which is highly desirable for in vivo detection of β-amyloid fibrils. PAD-1 displayed a turn-on effect, showing significant enhancement in fluorescence when bound to the aggregated β-amyloid fibrils. It also showed specific labeling of β-amyloid deposits in APP/PS1 transgenic mouse brains. Thus, PAD-1 proved to be a valuable alternative to ThT for cerebral β-amyloid detection and may enable quantitative imaging in vivo.

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