Figure 4.

(A) Fluorescence changes of DFHBFSI (3 μM) in response to G-quadruplex (15 μM), double-strand (15 μM) and single-strand oligonucleotides (15 μM). F and F₀ are the fluorescence intensity of DFHBFSI in the presence and absence of the oligonucleotides, respectively. (B) Fluorescence responses of G-quadruplex-specific dyes (3 μM) toward different kinds of oligonucleotides (15 μM). (C) Reversible topological switch between parallel and anti-parallel G-quadruplexes. (D) Real-time monitoring the topological switch of G4 based on DFHBFSI-PW17 (1 μM). K⁺, 2 mM; Mg²⁺, 50 mM; Pb²⁺, 150 μM; EDTA, 150 μM.