Characterization and application to the detection of single-stranded DNA binding protein of fluorescent DNA-templated copper/silver nanoclusters

A simple strategy for the preparation of strongly fluorescent and stable DNA-Cu/Ag NCs from reduction of AgNO₃ and Cu(NO₃) ₂ by NaBH₄ in the presence of DNA having a sequence 5'-CCCTTAATCCCC-3' has been demonstrated. Fluorescence, absorption, X-ray photoelectron spectroscopy (XPS), and electrospray ionization-mass spectrometry (ESI-MS) measurements have been applied to the characterization of the DNA-Cu/Ag NCs. The ESI-MS data reveal that each DNA-Cu/Ag NC contained 2 Ag and 1 Cu atoms. The interactions among DNA with the Ag and Cu atoms are further supported by the data of low-temperature fluorescence. In the presence of Cu²⁺ ions, the reaction time is 1.5 h, which is much shorter than that (120 h) for the preparation of Ag-DNA NCs that are prepared in a mixture of AgNO ₃, NaBH₄ and DNA without containing Cu²⁺ ions. Relative to the DNA-Ag NCs, the DNA-Cu/Ag NCs have greater fluorescence (quantum yield 51.2% vs. 11.5%). The DNA-Cu/Ag NCs are highly sensitive and selective for the detection of single-stranded DNA binding protein (SSB), with a linear range 1-50 nM and a limit of detection 0.2 nM at a signal-to-ratio of 3.