Y-type, C-rich DNA probe for electrochemical detection of silver ion and cysteine

An electrochemical assay for the detection of silver ion was reported, which was based on the interaction of the Y-type, C-rich ds-DNA with Ag+. Upon addition of Ag+, Y-type, C-rich ds-DNA could form an intramolecular duplex, in which Ag+ can selectively bind to cytosine–cytosine (C–C) mismatches forming C–Ag+–C complex. The binding result was evaluated by electrochemical impedance spectroscopy (EIS) and analyzed with the help of Randles' equivalent circuits. The differences of charge transfer resistance, ΔRCT, after and before the addition of Ag+, allows the detection and quantitative analysis of Ag+ with a detection limit of 10 fM. Moreover, cysteine (Cys) was applied to remove Ag+ from the C–Ag+–C complex, which allowed the Ag+ sensor to be reproduced. In the same way, ΔRCT for the C–Ag+–C system in the absence and presence of Cys allows the detection of Cys at a concentration as low as 100 fM. Finally, the potential application of the Ag+ sensor was also explored, such as in lake and drinking water.