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, Delta R-CT, 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, DRCT 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.