The most common working mechanism of photodynamic therapy is based on high-toxicity singlet oxygen, which is called Type II photodynamic therapy. But it is highly dependent on oxygen consumption. Recently, Type I photodynamic therapy has been found to have better hypoxia tolerance to ease this restriction. However, few strategies are available on the design of Type I photosensitizers. We herein report an unexpected strategy to alleviate the limitation of traditional photodynamic therapy by biotinylation of three photosensitizers (two fluorescein-based photosensitizers and the commercially available Protoporphyrin). The three biotiylated photosensitizers named as compound 1, 2 and 3, exhibit impressive ability in generating both superoxide anion radicals and singlet oxygen. Moreover, compound 1 can be activated upon low-power white light irradiation with stronger ability of anion radicals generation than the other two. The excellent combinational Type I / Type II photodynamic therapy performance has been demonstrated with the photosensitizers 1. This work presents a universal protocol to provide tumor-targeting ability and enhance or trigger the generation of anion radicals by biotinylation of Type II photosensitizers against tumor hypoxia.
Aggregation-caused quenching (ACQ)
and poor photostability in aqueous
media are two common problems for organic fluorescence dyes which
cause a dramatic loss of fluorescence imaging quality and photodynamic
therapy (PDT) failure. Herein, a local hydrophobic cage is built up
inside near-infrared (NIR) cyanine-anchored fluorescent silica nanoparticles
(FSNPs) in which a hydrophobic silane coupling agent (n-octyltriethoxysilane, OTES) is doped into FSNPs for the first time
to significantly inhibit the ACQ effect and inward diffusion of water
molecules. Therefore, the obtained optimal FSNP-C with OTES-modification
can provide hydrophobic repulsive forces to effectively inhibit the
π–π stacking interaction of cyanine dyes and simultaneously
reduce the formation of strong oxidizing species (•OH and H2O2) in reaction with H2O, resulting
in the best photostability (fluorescent intensity remained at 90.1%
of the initial value after 300 s of laser scanning) and a high PDT
efficiency on two- and three-dimensional (spheroids) HeLa cell culture
models. Moreover, through molecular engineering (including increasing
covalent anchoring sites and steric hindrance groups of cyanine dyes),
FSNP-C exhibits the highest fluorescent intensity both in water solution
(12.3-fold improvement compared to free dye) and living cells due
to the limitation of molecular motion. Thus, this study provides an
effectively strategy by combining a local hydrophobic cage and molecular
engineering for NIR FSNPs in long-term bright fluorescence imaging
and a stable PDT process.
A new photon up-conversion system with a TADF fluorescein derivative as a photosensitizer was developed to achieve a quite large anti-Stokes shift from red to blue with a fairly high up-conversion emission quantum yield.
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