Imaging mRNA Expression in Live Cells via PNA·DNA Strand Displacement-Activated Probes
Schematic representation of cSCK-mediated delivery of strand-displacement-activated PNA·DNA probes for imaging mRNA in living cells. (a) The probes consist of a fluorescently labeled nondegradable antisense PNA (peptide nucleic acid) hybridized to a shorter negatively charged complementary DNA strand bearing a quencher, leaving a short single-stranded section of PNA (the toehold). The nonfluorescent PNA∙DNA duplex probe is then electrostatically bound to the cationic-shell-crosslinked knedel-like nanoparticle (cSCK). The positive nature of the cSCK facilitates its endocytosis, and the presence of unprotonated amines facilitates disruption of the endosome by the proton-sponge effect which enables the strand-displacement probe to escape into the cytoplasm. Binding of the toe-hold portion of the PNA to the target mRNA sequence then facilitates strand displacement of the quenching DNA strand by branch migration and results in restoration of fluorescence to the PNA strand. (b) Structure of the cSCK formed by crosslinking the block copolymers following micellization , , .
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