Complex Resonant Scattering Behavior in the Surface Plasmon Resonance Imaging Microscopy of Single Gold Nanorods.

Diffraction patterns observed in surface plasmon resonance imaging (SPRI) microscopy measurements of single gold nanorods (AuNRs) exhibit a complex behavior at wavelengths near the longitudinal plasmonic resonance band. SPRI microscopy measurements at 814 nm from AuNRs in three samples with resonance extinction maxima at 670, 816, and 980 nm reveal a variety of diffraction patterns with central peaks that are either positive, negative, or biphasic. A unitless ratio parameter MR (-1 ≤ MR ≤ 1) is created to describe the distribution of diffraction patterns. A purely negative (MR = -1) central peak is observed for 30%, 57%, and 98% of the diffraction patterns in the 670, 816, and 980 nm samples, respectively. These results along with a theoretical modeling of the diffraction patterns with an anisotropic complex scattering coefficient suggests that this behavior only occurs for AuNRs when the laser wavelength used in SPRI experiments is shorter than the AuNR plasmonic resonance maxima, that is, in the anomalous dispersion region.

Investigation of Protective Properties of Organic Layers toward Reactive Oxygen Species.

The antioxidant protective properties of polyaromatic organic layers were evaluated toward reactive oxygen species (ROS) using scanning electrochemical microscopy in a foot-printing strategy. The layers were prepared by electrografting of aryldiazonium salts. Where p-(methyl)phenyl films show only weak protective properties toward ROS, p-(ethynyl)phenyl films evidence efficient protection of the covered surfaces. Applied potentials and electrolytes used during oxygen reduction reaction are critical parameters to control, prevent, or reduce the influence of ROS production and hence enhance the device lifetime.

Molecular Sieving and Current Rectification Properties of Thin Organic Films.

For the purpose of preparing well-organized functional surfaces, carbon and gold substrates were modified using electroreduction of a tetrahedral-shape preorganized tetra-aryldiazonium salt, leading to the deposition of ultrathin organic films. Characterization of the modified surfaces has been performed using cyclic voltammetry, X-ray photoelectron spectroscopy, infrared absorption spectroscopy, ellipsometry, atomic force microscopy, and contact angle measurements. The specific design of the tetra-aryldiazonium salts leads to an intrinsic structuring of the resulting organic films, allowing molecular sieving and current rectification properties toward redox probes in solution.