Electronic properties of nanoentities revealed by electrically driven rotation.

Direct electric measurement via small contacting pads on individual quasi-one-dimensional nanoentities, such as nanowires and carbon nanotubes, are usually required to access its electronic properties. We show in this work that 1D nanoentities in suspension can be driven to rotation by AC electric fields. The chirality of the resultantrotation unambiguously reveals whether the nanoentities are metal, semiconductor, or insulator due to the dependence of the Clausius-Mossotti factor on the material conductivity and frequency. This contactless method provides rapid and parallel identification of the electrical characteristics of 1D nanoentities.

Electrochemical stability of elemental metal nanoparticles.

The corrosion behavior of nanometer-scale solids is important in applications ranging from sensing to catalysis. Here we present a general thermodynamic analysis of this for the case of elemental metals and use the analysis to demonstrate the construction of a particle-size-dependent potential-pH diagram for the case of platinum. We discuss the data set required for the construction of such diagrams in general and describe how some parameters are accessible via experiment while others can only be reliably determined from first-principles-based electronic structure calculations. In the case of Pt, our analysis predicts that particles of diameter less than approximately 4 nm dissolve via the direct electrochemical dissolution pathway, Pt --> Pt(2+) + 2e(-), while larger particles form an oxide. As an extension of previously published work by our group, electrochemical scanning tunneling microscopy is used to examine the stability of individual Pt-black particles with diameters ranging from 1 to 10 nm. Our experimental results confirm the thermodynamic predictions, suggesting that our analysis provides a general framework for the assessment of the electrochemical stability of nanoscale elemental metals.

Subcellular-resolution delivery of a cytokine through precisely manipulated nanowires.

Precise delivery of molecular doses of biologically active chemicals to a pre-specified single cell among many, or a specific subcellular location, is still a largely unmet challenge hampering our understanding of cell biology. Overcoming this could allow unprecedented levels of cell manipulation and targeted intervention. Here, we show that gold nanowires conjugated with a cytokine such as tumour-necrosis factor-alpha can be transported along any prescribed trajectory or orientation using electrophoretic and dielectrophoretic forces to a specific location with subcellular resolution. The nanowire, 6 microm long and 300 nm in diameter, delivered the cytokine and activated canonical nuclear factor-kappaB signalling in a single cell. Combined computational modelling and experimentation indicated that cell stimulation was highly localized to the nanowire vicinity. This targeted delivery method has profound implications for controlling signalling events on the single cell level.