Nanomolar suspensions of Au nanorods were analyzed by photon correlation spectroscopy (PCS) complemented by optical absorption spectroscopy. We observed a wavelength-dependent enhancement of the anisotropic scattering as a consequence of the excitation of a longitudinal plasmon mode. The strong scattering intensity near the longitudinal surface plasmon resonance (LSPR) frequency for rods oriented parallel to the excitation optical field allowed the resolution of the translational anisotropy in an isotropic medium. Estimations of lengths and thicknesses of the Au nanorods from both translational and rotational diffusion coefficients were in qualitative agreement with values from transmission electron microscopy images. This wavelengthdependent anisotropic light scattering opens up new applications such as probing dynamics in complex environments at a single-particle level by depolarized PCS and sorting plasmonic nanoparticles according to their size/shape by polarized microscopy.

An improved setup including a measuring cell was designed for time-resolved surface-enhanced resonance Raman (SERR) spectroscopy. The cell is based on a rotating disk electrode (RDE) made from electrochemically roughened Ag. Cytochrome c (cc) adsorbed on a monolayer of mercaptoethanol is investigated with respect to heterogeneous electron transfer. Cyclic voltammograms and potential-dependent static SERR spectra indicate cc to be electroactive on the Ag electrode. The standard redox potential was found to be 234 mV. Time-resolved SERR spectra were then measured triggered by periodic potential pulses changing the protein between the oxidized and reduced state at a frequency of 10 Hz. Monoexponential functions obtained from the intensity of the band at 1361 cm-1 plotted versus time yielded the rate constants of heterogeneous electron transfer to be k(ox) = 46 +/- 7 s(-1) and k(red) = 84 +/- 20 s(-1). These relatively low rates are in line with the orientation of cc on the mercaptoethanol-modified Ag electrode. In this case the heme cleft pointed away from the surface thus hampering electron transfer.

Cytochrome c oxidase (CcO) from Paracoccus denitrificans was immobilized in a strict orientation via a his-tag attached to subunit I on a gold film and reconstituted in situ into a protein-tethered bilayer lipid membrane. In this orientation, the cytochrome c (cyt c) binding site is directed away from the electrode pointing to the outer side of the protein-tethered bilayer lipid membrane architecture. The CcO can thus be activated by cyt c under aerobic conditions. Catalytic activity was monitored by impedance spectroscopy, as well as cyclic voltammetry. Cathodic and anodic currents of the CcO with cyt c added to the bulk solution were shown to increase under aerobic compared to anaerobic conditions. Catalytic activity was considered in terms of repeated electrochemical oxidation/reduction of the CcO/cyt c complex in the presence of oxygen. The communication of cyt c bound to the CcO with the electrode is discussed in terms of a hopping mechanism through the redox sites of the enzyme. Simulations supporting this hypothesis are included.