A sensitive fluorometric sensor for Ag⁺ based on the hybridization chain reaction coupled with a glucose oxidase...

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.