A sensitive fluorometric sensor for Ag+ based on the hybridization chain reaction coupled with a glucose oxidase dual-signal amplification strategy.

Abstract

In this work, an efficient and sensitive fluorometric sensor was developed to detect silver ions (Ag+). It is based on the cytosine–Ag+–cytosine (C–Ag+–C) structure via a dual-signal amplification strategy using glucose oxidase (GOx) and the hybridization chain reaction (HCR). A silver-coated glass slide (SCGS) acts as an ideal material for separation. Cytosine rich (C-rich) capture DNA (C-DNA) assembled themselves on the SCGS via Ag–S bonds and hybridized with signal DNA (S-DNA) to trigger the HCR. With specific base-pairing, the S-DNA and HCR products bind on the SCGS. Then, the GOx–biotin–streptavidin (SA) complexes bind to the HCR products through SA–biotin interactions. Owing to the formation of a particular C–Ag+–C structure between two neighboring C-rich C-DNA on the SCGS, the C-DNA/S-DNA/HP1-GOx/HP2-GOx complex gradually moved away from the SCGS as the concentration of Ag+ increased and the combined GOx fell into the buffer. H2O2 could be generated during the oxidation of glucose, catalyzed by GOx in the buffer. Afterward, H2O2 could oxidize the substrate (3-(p-hydroxyphenyl)-propanoic acid) when Horseradish peroxidase was present, giving rise to blue fluorescence. The proposed strategy reached a limit of detection (LOD) of 1.8 pmol L−1 with a linear detection range of 5 to 1000 pmol L−1 for Ag+. Moreover, this assay has been commendably used for the detection of Ag+ in actual samples with fairly good results.