Self-Assembly of Folate
onto Polyethyleneimine-Coated
CdS/ZnS Quantum Dots for Targeted Turn-On Fluorescence Imaging of
Folate Receptor Overexpressed Cancer Cells
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Abstract
Folate receptor (FR) can be overexpressed by a number
of epithelial-derived
tumors, but minimally expressed in normal tissues. As folic acid (FA)
is a high-affinity ligand to FR, and not produced endogenously, development
of FA-conjugated probes for targeted imaging FR overexpressed cancer
cells is of significance for assessing cancer therapeutics and for
better understanding the expression profile of FR in cancer. Here
we report a novel turn-on fluorescence probe for imaging FR overexpressed
cancer cells. The probe was easily fabricated via electrostatic self-assembly
of FA and polyethyleneimine-coated CdS/ZnS quantum dots (PEI-CdS/ZnS
QDs). The primary fluorescence of PEI-CdS/ZnS QDs turned off first
upon the electrostatic adsorption of FA onto PEI-CdS/ZnS QDs based
on electron transfer to produce negligible fluorescence background.
The presence of FR expressed on the surface of cancer cells then made
FA desorb from PEI-CdS/ZnS QDs due to specific and high affinity of
FA to FR. As a result, the primary fluorescence of PEI-CdS/ZnS QDs
adhering to the cells turned on due to the inhibition of electron
transfer. The most important merits of the developed probe are its
simplicity and the effective avoidance of the false positive results
due to the simple electrostatic self-assembly of FA onto the surface
of PEI-CdS/ZnS QDs and the involved fluorescence “off-on”
mechanism. The probe was demonstrated to be sensitive and selective
for targeted imaging of FR overexpressed cancer cells in turn-on mode