Figure 7.

Schematic representation of the novel strategy for in vivo cancer imaging using activatable aptamer probe (AAP) based on cell membrane pro- tein-triggered conformation alteration. The AAP consists of three fragments: a cancer-targeted aptamer sequence (A-strand), a poly-T linker (T-strand), and a short DNA sequence (C-strand) complementary to a part of the A-strand, with a fluorophore and a quencher attached at either terminus. In the absence of a target, the AAP is hairpin structured, resulting in a quenched fluorescence. When the probe is bound to membrane receptors of the target cancer cell, its conformation is altered, thus resulting in an activated fluorescence signal. Reprinted with permission from ref. 65. Copyright (2011) PNAS.