title: Methylene blue as a G-quadruplex binding probe for label-free homogeneous electrochemical biosensing.
abstract: Herein, G-quadruplex sequence was found to significantly decrease the diffusion current of methylene blue (MB) in homogeneous solution for the first time. Electrochemical methods combined with circular dichroism spectroscopy and UV-vis spectroscopy were utilized to systematically explore the interaction between MB and an artificial G-quadruplex sequence, EAD2. The interaction of MB and EAD2 (the binding constant, K ≈ 1.3 × 10(6) M(-1)) was stronger than that of MB and double-stranded DNA (dsDNA) (K ≈ 2.2 × 10(5) M(-1)), and the binding stoichiometry (n) of EAD2/MB complex was calculated to be 1.0 according to the electrochemical titration curve combined with Scatchard analysis. MB was proved to stabilize the G-quadruplex structure of EAD2 and showed a competitive binding to G-quadruplex in the presence of hemin. EAD2 might mainly interact with MB, a positive ligand of G-quadruplex, through the end-stacking with π-system of the guanine quartet, which was quite different from the binding mechanism of dsDNA with MB by intercalation. A novel signal read-out mode based on the strong affinity between G-quadruplex and MB coupling with aptamer/G-quadruplex hairpin structure was successfully implemented in cocaine detection with high specificity. G-quadruplex/MB complex will function as a promising electrochemical indicator for constructing homogeneous label-free electrochemical biosensors, especially in the field of simple, rapid, and noninvasive biochemical assays.
authors.affiliation: Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry, Peking University , Beijing 100871, China.
authors.forename: Fang-Ting
authors.initials: FT
authors.lastname: Zhang
authors.forename: Ji
authors.initials: J
authors.lastname: Nie
authors.forename: De-Wen
authors.initials: DW
authors.lastname: Zhang
authors.forename: Ji-Tao
authors.initials: JT
authors.lastname: Chen
authors.forename: Ying-Lin
authors.initials: YL
authors.lastname: Zhou
authors.forename: Xin-Xiang
authors.initials: XX
authors.lastname: Zhang
mesh_terms: D052157:Aptamers, Nucleotide / Q000737:chemistry*; D001667:Binding, Competitive; D015374:Biosensing Techniques; D003042:Cocaine / Q000302:isolation & purification*; D004247:DNA / Q000737:chemistry; D055664:Electrochemical Techniques; D054856:G-Quadruplexes; D006427:Hemin / Q000737:chemistry; D008751:Methylene Blue / Q000737:chemistry*; D012996:Solutions
chemical_list: D052157:Aptamers, Nucleotide; D012996:Solutions; D006427:Hemin; D004247:DNA; D003042:Cocaine; D008751:Methylene Blue