Abstract
Although biological fluorescence imaging in the second
near-infrared window (NIR-Ⅱ, 1000-1700 nm) has embodied the advantages of deep
tissue penetration, low background noise and high spatial resolution, shortage
of high quantum yield (QY) organic fluorophores has become the bottleneck for
further development to this field. Now, an ingenious strategy is proposed to
address this: constitutional isomerization by utilizing the molecular design
philosophy of aggregation-induced emission (AIE). By solely shifting alkyl
chain from meta to ortho position, the resulting twisted
structure drives the NIR-Ⅱ fluorophores from aggregation-caused quenching (ACQ)
to AIE. In this way, the AIE luminogen (AIEgen), 2TT-oC6B, is provided with an emission peak at 1030 nm and a QY of 11%
in nanoparticles, one of the highest reported so far. To endow the targeting
ability to deeply located diseases, neutrophils (NEs), the most common immune
cells, are used to penetrate the brain tissues. Herein, we show that NEs
carrying 2TT-oC6B NPs can penetrate
the brain and visualize the deeply located inflammation through intact scalp
and skull (3 mm of depth). Notably, the bright 2TT-oC6B fluorophore contributes to a significantly enhanced
signal-to-noise ratio of 30.6 in brain inflammation site, which is among the
best ones to date. This modern molecule design philosophy could enable a
powerful platform for high QY fluorophores and their potential biological
applications.
Supplementary materials
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