Effects of polymorphic DNA on the fluorescent properties of silver nanoclusters

Silver nanoclusters (Ag NCs) with emission wavelengths from 538 nm to 706 nm were synthesized using a series of G-/C-rich polymorphic DNA templates. Thermodynamic studies on the interactions of Ag+ with polymorphic DNA indicate that the binding affinities greatly depend on the secondary structures of DNA templates, with a decreasing order: the coiled C-rich strand > the i-motif > the duplex > the G-quadruplex. Fluorescent Ag NCs prepared using these polymorphic DNA templates show that fluorescence stabilities are associated with the binding affinities between DNA templates and Ag+, e.g., the coiled C-rich strand C4A4C3 with the highest binding constant (40.2 × 105 M−1) stabilizes Ag NCs for over 300 h, while the G-quadruplex G4T4G4 with the lowest binding constant (0.64 × 105 M−1) generates Ag NCs with the shortest shelf-life (55 h). The cluster sizes of Ag NCs are associated with the sequence lengths of DNA templates. In addition, the red emitting [C4A4C3]-Ag and the NIR emitting [G4T4G4-C4A4C4]-Ag are successfully used for HeLa cell transfection and exhibit good intracellular emission. These results provide a promising pathway to prepare silver nanomaterials with desirable physicochemical properties through designing suitable DNA templates.