Fluorometric detection of silver(I) using cytosine-Ag(I)-cytosine pair formation, DNA assembly and theAND logic operation of amultiple-componentDNAzyme

A nonenzymatic fluorometric assay is described for highly sensitive and selective detection of silver ion. It is making use of a controlled DNA assembly and an AND logic operation of a multiple-component DNAzyme (MNAzyme). It corresponds to an Ag(I)-responsive three-way junction (3-WJ) assembly. The tailored probes of the 3-WJ architecture were designed with complementary domains for subsequent assembly. Cytosine (C)-cytosine mismatches at one-way junction were set as the sensing element for Ag(I). Upon exposure to Ag(I) as an input, C-Ag(I)-C pairs are being formed. This enhances the binding energy between these separate probes and thus promotes the formation of a nanostructure that represents an AND logic assembly of MNAzyme with an amplified output signal. This results in an Ag(I)-induced increase in fluorescence which is measured best at excitation/ emission maxima of 645/ 670 nm. The method displays high selectivity and sensitivity, has a 5 pM detection limit at 3s and a dynamic range that extends from 10 pM to 100 nM.