Abstract
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 dually-amplify signal via chemiluminescence resonance energy transfer (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.
Highlights
Turn-on fluorescence imaging is routinely studied; turn-on chemiluminescence has been rarely explored for in vivo imaging
We have proposed a tentative mechanism for the auto-oxidation in Fig. 2e, in which O2 is added to the doublebond of imidazole moiety to form an unstable intermediate that further decomposes into ADLumin-3 and releases photons
We noticed that the chemiluminescence signals from eyes were higher (1.6-fold) in the 5xFAD group than that in WT group (Fig. 6c, d). This is consistent with our previous report, in which we showed that near infrared fluorescence imaging (NIRF) probe CRANAD-X (X = −2, −3, −30, −58, and −102) could detect the Aβ content in eyes[56]
Summary
Turn-on fluorescence imaging is routinely studied; turn-on chemiluminescence has been rarely explored for in vivo imaging. The excitation light generates relatively much stronger emission signals from fluorophores at shallow locations, which contain nonspecifically accumulated imaging probe and auto-fluorescent molecules These excitation-related limitations of NIRF imaging are significantly contributed to low signal to noise ratio (SNR) and poor tissue penetration. Compared to fluorescence imaging, chemiluminescence imaging is being applied far less in biological studies, primarily due to its low sensitivity and irreversibility of the probes Another drawback of chemiluminescence is the need of a chemical reaction to produce the emission light[8,9,10,11,12,13,14,15]. To overcome the limitation of short emission of ADLumin-1, we demonstrate the feasibility to achieve dual-amplification of signal via chemiluminescence resonance energy transfer (termed as DAS-CRET) with two nonconjugated smart probes in solutions, tissues and brain homogenates, and in vivo whole brain imaging. We believe that this technology can become a very important complimentary tool for preclinical studies and has potential for clinical studies (via ocular imaging) in the future
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