A highly sensitive and selective electrochemical DNA biosensor for detection of Ag+ was developed based on amplification of DNA-Au bio-bar codes and silver enhancement. Cytosine-rich single stranded DNA oligonucleotide (sub-DNA) was immobilized on the surface of the gold electrode via Au-S chemical interaction. In the presence of Ag+, with the interaction of cytosine-Ag+-cytosine (C-Ag+-C), cytosine-rich DNA oligonudeotide probes labeled AuNPs have a hybridization with sub-DNA and then form a duplex-like structure, following the AuNPs-catalyzed silver enhancement. The whole detection procedure of Ag+ based on the developed biosensor was evaluated by electrochemical techniques. Owing to the hybridization of sandwich assay format and distinct electrochemical signal amplification of silver enhancement, the proposed biosensors exhibited a good analytical performance for sensitive transduction of Ag+ recognition with a wide detection linear range from 5 pM to 50 mu M, and a low detection limit of 2 pM. The developed biosensor was highly selective and its practical applicability in real water samples was also tested with satisfactory results. (C) 2016 Elsevier B.V. All rights reserved.