Stability of Scanning Tunneling Microscopy Tip-Induced Bimetallic Nanoclusters: Influence of Hardness and Composition on the Cohesive Energies

Phase Diagram of Continuous Binary Nanoalloys: Size, Shape, and Segregation Effects

The phase diagrams of continuous binary nanoalloys are important in providing guidance for material designs and industrial applications. However, experimental determination of the nano-phase diagram is scarce since calorimetric measurements remain quite challenging at the nanoscale. Based on the size-dependent cohesive energy model, we developed a unified nano-thermodynamic model to investigate the effects of the size, shape, and segregation on the phase diagrams of continuous binary nanoalloys. The liquidus/solidus dropped in temperature, two-phase zone was narrowed, and the degree of surface segregation decreased with decrease in the size or increase in the shape factor. The congruent melting point of Cu-Au nanoalloys with and without segregation is linearly shifted to higher Au component and lower temperature with decreasing size or increasing shape factor. By reviewing surface segregated element of different binary nanoalloys, two segregation rules based on the solid surface energy and atomic size have been identified. Moreover, the established model can be employed to describe other physicochemical properties of nanoalloys, e.g. the cohesive energy, catalytic activation energy, and order-disorder transition temperature, and the validity is supported by available other theoretical prediction, experimental data and molecular dynamic simulations results. This will help the experimentalists by guiding them in their attempts to design bimetallic nanocrystals with the desired properties.

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 AgNO(3) and Cu(NO(3))(2) by NaBH(4) 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 Cu(2+) 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), NaBH(4) and DNA without containing Cu(2+) 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.