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The elastic modulus of ZnO nanowires was measured using a resonance method based on laser Doppler effect and their fracture strains were determined via two-point bending with the aid of optical nanomanipulation. The elastic moduli of ZnO nanowires with diameters of 78 to 310 nm vary from 123 to 154 GPa, which are close to the bulk value of 140 GPa and independent of the diameters and surface defects. However, the fracture strains of the ZnO nanowires depend significantly on their diameters, increasing from 2.1% to 6.0% with the decrease in diameter from 316 to 114 nm. Post-mortem TEM analysis of the ends of the fractured nanowires revealed that fracture initiated at surface defects. The Weibull statistical analysis demonstrated that a greater defect depth led to a smaller fracture strain. The surface-defect dominated fracture should be an important consideration for the design and application of nanowire-based nanoelectromechanical systems.

The interfacial adhesion behaviour of a ZnO nanowire-Si substrate system is investigated using an in situ scanning electron microscope (SEM) mechanical peeling technique. The peel front of a nanowire advances via stick-slip events, and an equilibrium between the driving and resistant force to separation occurs immediately prior to a slip event. The interfacial adhesion energy is one order higher than that predicted theoretically by van der Waals interactions. The enhanced adhesion is primarily attributed to chemical and electrostatic interfacial interactions induced by electron irradiation. This work demonstrates that the operating environment of a nanoscale system could dramatically influence its adhesion behaviour. These findings are expected to have significant implications for interpreting the adhesion behaviour exhibited by a 1D nanostructure-substrate system when applying different testing methodologies, and for the fabrication of future NEMS devices.

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Genetic tags allow rapid localization of tagged proteins in cells and tissues. APEX, an ascorbate peroxidase, has proven to be one of the most versatile and robust genetic tags for ultrastructural localization by electron microscopy (EM). Here, we describe a simple method, APEX-Gold, which converts the diffuse oxidized diaminobenzidine reaction product of APEX into a silver/gold particle akin to that used for immunogold labelling. The method increases the signal-to-noise ratio for EM detection, providing unambiguous detection of the tagged protein, and creates a readily quantifiable particulate signal. We demonstrate the wide applicability of this method for detection of membrane proteins, cytoplasmic proteins, and cytoskeletal proteins. The method can be combined with different EM techniques including fast freezing and freeze substitution, focussed ion beam scanning EM, and electron tomography. Quantitation of expressed APEX-fusion proteins is achievable using membrane vesicles generated by a cell-free expression system. These membrane vesicles possess a defined quantum of signal, which can act as an internal standard for determination of the absolute density of expressed APEX-fusion proteins. Detection of fusion proteins expressed at low levels in cells from CRISPR-edited mice demonstrates the high sensitivity of the APEX-Gold method.