An ultrasensitive electrochemical method for detection of Ag+ based on cyclic amplification of exonuclease III activity on cytosine–Ag+–cytosine

Abstract

Ag⁺ is known to bind very strongly with cytosine–cytosine (C–C) mismatches in DNA duplexes to form C–Ag⁺–C base pairs. Exonuclease III (Exo III) can catalyze the stepwise removal of mononucleotides of duplex DNA. In this work, we study Exo III activity on DNA hybrids containing C–Ag⁺–C base pairs. Our experiments show that Ag⁺ ions could intentionally trigger the activity of Exo III towards a designed cytosine-rich DNA oligonucleotide (C-rich probe) by the conformational change of the probe. Our sensing strategy uses this conformation-dependent activity of Exo III, which is controlled through the cyclical shuffling of Ag⁺ ions between the solid DNA hybrid and the solution phase. This interesting conversion has led to the development of an ultrasensitive detection platform for Ag⁺ ions with a detection limit of 0.03 nM and a total assay time possible within minutes. This simple detection strategy could also be used for the detection of other metal ions which exhibit specific interactions with natural or synthetic bases.