Scheme 1.
Principle of 3′ → 5′ exonuclease activity assay. i) ExoIII digests DNA from the 3′-terminus, but is halted at the loop region; ii) The released guanine-rich sequence folds into a G-quadruplex; iii) G-quadruplex-selective probe crystal violet (CV) exhibits a “turn-on” emission response.