Fluorescence imaging in the second near-infrared window
(NIR-II,
1000–1700 nm) using small-molecule dyes has high potential
for clinical use. However, many NIR-II dyes suffer from the emission
quenching effect and extremely low quantum yields (QYs) in the practical
usage forms. The AIE strategy has been successfully utilized to develop
NIR-II dyes with donor–acceptor (D–A) structures with
acceptable QYs in the aggregate state, but there is still large room
for QY improvement. Here, we rationally designed a NIR-II emissive
dye named TPE-BBT and its derivative (TPEO-BBT) by changing the electron-donating
triphenylamine unit to tetraphenylethylene (TPE). Their nanoparticles
exhibited ultrahigh relative QYs of 31.5% and 23.9% in water, respectively.
By using an integrating sphere, the absolute QY of TPE-BBT nanoparticles
was measured to be 1.8% in water. Its crystals showed an absolute
QY of 10.4%, which is the highest value among organic small molecules
reported so far. The optimized D–A interaction and the higher
rigidity of TPE-BBT in the aggregate state are believed to be the
two key factors for its ultrahigh QY. Finally, we utilized TPE-BBT
for NIR-II photoluminescence (PL) and chemiluminescence (CL) bioimaging
through successive CL resonance energy transfer and Förster
resonance energy transfer processes. The ultrahigh QY of TPE-BBT realized
an excellent PL imaging quality in mouse blood vessels and an excellent
CL imaging quality in the local arthrosis inflammation in mice with
a high signal-to-background ratio of 130. Thus, the design strategy
presented here brings new possibilities for the development of bright
NIR-II dyes and NIR-II bioimaging technologies.
Fluorescence-guided photodynamic therapy (PDT) has been
considered
as an emerging strategy for precise cancer treatment by making use
of photosensitizers (PSs) with reactive oxygen species (ROS) generation.
Some efficient PSs have been reported in recent years, but multifunctional
PSs that are responsive to cancer-specific biomarkers are rarely reported.
In this study, we introduced a phosphate group as a cancer-specific
biomarker of alkaline phosphatase (ALP) on a PS with the features
of aggregation-induced emission (AIE) for cancer cell imaging and
therapy. In cancer cells with high ALP expression, the phosphate group
on the AIE probe is selectively hydrolyzed by ALP. Consequently, the
hydrophobic probe residue is aggregated in aqueous media and gives
a “turn on” fluorescent response. Moreover, fluorescence-guided
PDT was realized by the aggregates of probe residue with strong ROS
generation efficiency under white light irradiation. Overall, this
work presents a strategy of applying ALP-responsive AIE PS for specific
imaging cancer cells and succeeding with specific PDT upon the cancer
biomarker stimulated responsive reactions.
Cell death is closely related to various diseases, and monitoring and controlling cell death is a promising strategy to develop efficient therapy. Aggregationinduced emission luminogens (AIEgens) are ideal candidates for developing novel theranostic agents because of their intriguing properties in the aggregate state. The rational application of AIE materials in cell death-related research is still in its infancy but has shown great clinical potential. This review discussed the research frontier and our understanding of AIE materials in various subroutines of cell death, including apoptosis, necrosis, immunogenic cell death, pyroptosis, autophagy, lysosomedependent cell death, and ferroptosis. We hope that the new insights can be offered to this growing field and attract more researchers to provide valuable contributions.
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