Fluorescent materials are widely employed in biological analysis owing to their biorthogonal chemistries for imaging and sensing purposes. However, it is always a challenge to design fluorophores with desired photophysical and biological properties, due to their complicated molecular and optical nature. Inspired by anthocyanidin, a class of flower pigments, we designed a new fluorescent molecular framework, AC-Fluor. The new fluorescent materials can be rationally engineered to produce a broad range of fluorescent scaffolds with flexibly tunable emission spectra covering the whole visible light range, from 467 to 707 nm. Furthermore, they exhibit unprecedented environment-insensitive two-photon properties with a substantial cross section as large as 1100 GM in aqueous solution. AC-Fluors demonstrate their biological values through two-photon deep tissue imaging, with penetration depths as much as 300 μm, while exhibiting minimal cytotoxicity. These features engender a rational engineering strategy for the design and optimization of new fluorescent materials for biological imaging.
Fluorescence molecular imaging has attracted increasing
attention
due to its various advantages. Lots of fluorophores have been developed
to meet various molecular imaging needs. However, it is still inconvenient
due to the lack of excellent fluorophores with an optically tunable
group for biological molecular imaging. Here a new platform of a versatile
long wavelength fluorophore with an optically tunable hydroxyl group
was successfully developed by regulating molecular planarity and the
twisted intramolecular charge transfer effect with a protected and
deprotected hydroxyl group approach via “step by step”
modifying strategy. As an excellent representative of this new type
of fluorophore, LDOH-4 possesses good chemical and optical properties
and shows a potential application prospect. As a proof-of-concept,
a nitroreductase-activated TP fluorescent probe LDO-NTR was designed,
which not only sensitively recognizes NTR with more than 310-fold
response signal enhancement in vitro but also tracks NTR in a hypoxia
tumor mouse model in vivo by using two-photon imaging. It is hopeful
that the long wavelength fluorophore with the optically tunable hydroxyl
group can serve as a useful platform to extend capable detection tools
in biological chemistry and biomedical applications.
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