This
study investigated a selective and sensitive theragnosis system
for the specific targeting of the membrane and nuclei based on visible-light
and pH-responsive TiO2-integrated cross-linked carbon dot
(C-CD/TiO2) for tumor detection and controllable photothermal
therapy. The cross-linking system was formed by boronate ester linkages
between the TiO2-immobilized Dopa-decyl (D-CD) and zwitterionic-formed
CD (Z-CD) for nuclear targeting, which showed fluorescence “off”
at physiological pH. The fluorescence recovered to the “on”
state in acidic cancer cells owing to cleavages of the boronate ester
bonds, resulting in the disruption of the Förster resonance
energy transfer that generated different CDs useful for tumor-selective
biosensors and therapy. D-CD, which is hydrophobic, can penetrate
the hydrophobic sites of the cell membrane; it caused a loss in the
hydrophobicity of these sites after visible-light irradiation. This
was achieved by the photocatalytic activity of the TiO2 modulating energy bandgap, whereas the Z-CD targeted the nucleus,
as confirmed by merged confocal microscopy images. D-CD augmented
by photothermal heat also exhibited selective anticancer activity
in the acidic tumor condition but showed only minimal effects at a
normal site at pH 7.4. After C-CD/TiO2 injection to an in vivo tumor model, C-CD/TiO2 efficiently ablated
tumors under NIR light irradiation. The C-CD/TiO2 group
showed up-regulation of the pro-apoptotic markers such as P53 and BAX in tumor. This material exhibited
its potential as a theragnostic sensor with excellent biocompatibility,
high sensitivity, selective imaging, and direct anticancer activity
via photothermal therapy.
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