Figure 14.

(A) Poly-T oligonucleotides tethered on one end on the electrode surface, and labeled on the other end with a ferrocenyl moiety. Upon addition of Hg²⁺, poly-T strands become rigid, drawing Fc away from the surface. Reprinted with permission from [110]. Copyright 2009 American Chemical Society; (B) DNA strand carrying a ferrocenyl tag at one end and immobilized on a gold electrode at its other end by a SH group. Under this conformation, the ferrocene is far from the surface and no current flows. A hairpin structure is induced if Hg²⁺ are present, by association between two T bases, which brings the Fc label close to the electrode surface. The sensor can be regenerated by simply unfolding the ferrocene-labeled DNA in 10 µM cysteine. Reproduced from [111] with permission of The Royal Society of Chemistry.