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Abstract
Fluorophores with donor-acceptor-donor groups with the emission spanning the second near-infrared window (NIR-II) have recently received great attention for biomedical application. Yet, the mechanism underlying the equilibrium between fluorescence (radiative decay) and photothermal effect (non-radiative decay) of these fluorophores remains elusive. Here, we demonstrate that a lipophilic NIR-II fluorophore, BPBBT, possesses both twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) characteristics. Human serum albumin (HSA) binds to BPBBT, which changes the planarity of the fluorophore and restricts its intramolecular rotation. The binding results in alteration to the equilibrium between AIE and TICT state of BPBBT, tailoring its fluorescence and photothermal efficiency. Under the guidance of intraoperative NIR-II fluorescence image, the prepared HSA-bound BPBBT nanoparticles delineate primary orthotopic mouse colon tumor and metastatic lesions with dimensions as small as 0.5 mm × 0.3 mm, and offer photothermal ablation therapy with optimized timing, dosing and area of the laser irradiation.
Highlights
Fluorophores with donor-acceptor-donor groups with the emission spanning the second nearinfrared window (NIR-II) have recently received great attention for biomedical application
Certain NIR-II fluorophores with D–A–D structures have recently been developed for dual NIR-II imaging and photoacoustic imaging[7] or dual NIR-II imaging and photothermal therapy[9]
The emission quantum yield (QY) of BPBBT in solvent decreased as the solvent polarity increased: hexane (8.72%) > toluene (5.56%) > chloroform (0.90%) > THF (0.72%) > DMF (0.42%) (Supplementary Methods and Supplementary Fig. 2a)
Summary
Fluorophores with donor-acceptor-donor groups with the emission spanning the second nearinfrared window (NIR-II) have recently received great attention for biomedical application. The intramolecular rotation increases the dihedral angle in the molecule and breaks the planar structure, which reduces radiative transition and greatly weakens fluorescence[19,20,21] This phenomenon is referred to as twisted intramolecular charge transfer (TICT). Introduction of aggregation-induced emission (AIE) groups (AIEgens) to the structure of D–A–D fluorophores, on the other hand, restricts intramolecular rotation and suppresses TICT, but increases fluorescence when aggregation in poor solvents[19,23,24,25]. TICT state weakens the fluorescence intensity but elevates the photothermal conversion ability of the fluorophores, while AIE state causes enhanced fluorescence intensity but decreased photothermal conversion effect These phenomena are determined by the nature of intramolecular rotation[19,22,26,27]. Under the guidance of NIR-II fluorescence imaging, BPBBT NPs allow the precisely controlled PTT of both primary and metastatic lesions through optimization of timing, dosing, and area of the laser irradiation, achieving a complete cure of the orthotopic colon tumor in mice
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