Ultrasensitive electrochemical biosensor for silver ion based on magnetic nanoparticles labeling with hybridization chain reaction amplification strategy

Silver ion (AgE) is a highly toxic heavy metal ion to aquatic organisms and accumulates in the human body via the food chain. Therefore, fast and accurate detection of Ag+ in water and food resources has become a critical issue within the scope of human health. Herein, we developed an ultrasensitive electrochemical biosensor for detection of Ag+ based on magnetic Fe3O4@gold core-shell nanoparticles (Fe3O4@Au NPs) labeling with hybridization chain reaction (HCR) amplification strategy. In this sensing strategy, the magnetic Fe3O4@Au NPs were selected for labeling with HCR product and enrichment on the surface of magnetic gold electrode. Thiolated-oligonucleotide (S1) was firstly immobilized on the surface of Fe3O4@Au NPs through Au-S chemical bond. In the presence of Ag+, cytosine-rich DNA oligonucleotide S2 hybridized with S1 to form an intramolecular duplex, in which Ag+ can selectively bind to cytosine-cytosine mismatches forming C-Ag+-C complex. The exposed stem of the C-Ag+-C complex opened two alternating ferrocene-labeled DNA hairpins (H-1 and H-2) in turn and triggered HCR to form a supersandwich DNA structure on the surface of Fe3O4@Au NPs. The HCR products modified Fe3O4@Au NPs were brought to the surface of magnetic gold electrode for direct electrochemical measurements. The proposed strategy led to a low detection limit of 0.5 fM and a wide dynamic range of 1 fM-100 pM for target Ag+. The developed biosensor was highly selective and its practical applicability in tap water and lake water samples was also investigated with a satisfactory result. (C) 2017 Elsevier B.V. All rights reserved.