One-Step Synthesis of DNA Templated Water-Soluble Au-Ag Bimetallic Nanoclusters for Ratiometric Fluorescence Detection of DNA.

DNA strands have been used as templates to form different sized silver nanoclusters. Although DNA templated silver nanoclusters (NCs) probes which show outstanding fluorescence properties have been widely applied in chemical sensing and cellular imaging, synthesis of DNA template Au-Ag bimetallic nanoclusters remains a challenge. A facile one-step synthesis method was thus developed in this study to form Au-Ag NCs using C4-ATAT-C4 as template. C4-ATAT-C4 acted as a stabilizer for preventing aggregation of the Au-Ag NCs. The obtained Au-Ag NCs stabilized by C4-ATAT-C4 showed bright fluorescence and high stability. A series of experiments showed that temperature, citrate-citric acid buffer, sequence and concentration of DNA played an important role in the synthesis of fluorescent Au-Ag NCs. In addition, a ratiometric fluorescence probe was designed through combining the nucleotide sequence (C4-ATAT-C4) and hybridization sequence in the presence of the double-strand-chelating dye Super SYBR Green (SG). The combination of prepared Au-Ag NCs, Super SG, and perfectly matched DNA emitted fluorescence at 500 and 590 nm, respectively, when the composite was excited at 290 nm. A gastric cancer gene was also selectively detected by our developed ratiometric fluorescence probe.