Abstract
Hot-band absorption (HBA)-induced anti-Stokes fluorescence (ASF) with longer-wavelength excitation is one effective pathway to deep penetration and low autofluorescence in intravital fluorescence imaging, raising demands for fluorophores with broad spectra, high absorption, and strong emission. However, typical fluorescent dyes display some emission quenching when their concentration is increased in order to obtain brighter fluorescence. In this work, the HBA-induced ASF of aggregation-induced emission (AIE) dots is reported. BPN-BBTD dots were synthesized and confirmed with a fluorescence enhancement and a considerable ASF intensity. In addition, the mechanism of ASF and the HBA process of BPN-BBTD dots were carefully validated and discussed. To obtain the full advantages of the long-wavelength excitation and the short fluorescence lifetime in deep-tissue bioimaging, a large-depth ASF confocal microscopic imaging of in vivo cerebral vasculature was conducted under the excitation of a 980 nm continuous wave laser after intravenous injection of BPN-BBTD dots. Meanwhile, the 3D structure of the cerebrovascular network was successfully reconstructed.
Highlights
Fluorescence imaging is a powerful tool for deep-penetration bioimaging due to its excellent resolution [1,2]
The small Stokes shift of BPN-BBTD dots held the possibility of thermally activated delayed fluorescence or hot-band absorption (HBA)-induced anti-Stokes fluorescence
aggregation-induced emission (AIE) dyes have the advantages of bright fluorescence and high photostability when encapsulated into dots, which is suitable for in vivo applications
Summary
Fluorescence imaging is a powerful tool for deep-penetration bioimaging due to its excellent resolution [1,2]. In contrast to the typical Stokes luminescence, anti-Stokes luminescence utilizes long-wavelength excitation light to emit short-wavelength photons which need additional energy. One source of additional energy is another excitation photon, as in the multi-photon absorption process and upconversion processes based on lanthanide or triplet–triplet annihilation [5,9,15,16,17]. Thermal photons are another source, as in the hot-band absorption (HBA) process and the thermally activated delayed fluorescence (TADF) process [14,18,19]. It could be an excellent strategy to combine AIE dyes with the HBA process in bioimaging
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