A Split DNA Scaffold for a Green Fluorescent Silver Cluster

Silver molecules are chromophores with diverse spectra and rich photophysics, and DNA strands act as ligands that develop specific molecular silver species. For example, C4AC4T*C3GT4 selectively yields a Ag106+ fluorophore with λex/λem = 490/550 nm. This single-stranded DNA coordinates and protects the cluster, and its integrity was challenged by breaking the phosphodiester backbone at the innocuous T*. The resulting C4AC4T and C3GT4 fragments also develop the same Ag106+ fluorophore but only when all three components (two fragments + Ag) are present. This C4AC4T/C3GT4/Ag106+ complex is favored by higher DNA concentrations and preferentially forms when hybridization forces C4AC4T and C3GT4 onto a shared DNA duplex. The C4AC4T/C3GT4 assembly reverses when the cluster photodegrades, which suggests that the cluster is labile. C4AC4T forms an alternate cluster at low temperatures, but C3GT4 recovers the λ = 490 nm fluorophore at higher temperatures. Thus, the reciprocal interactions between the host DNA strands and the cluster adduct combine to create a highly specific, split-DNA fluorescent Ag cluster capable of sensing target DNA sequences with high specificity and on–off contrast.