Redox-Switching in a Viologen-type Adlayer: An Electrochemical Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy Study on Au(111)-(1 x 1) Single Crystal Electrodes

We reported the first application of in situ shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) to an interfacial redox reaction under electrochemical conditions. We construct gap-mode sandwich structures composed of a thiol-terminated HS-6V6H viologen adlayer immobilized on a single crystal Au(111)-(1x1) electrode and covered by Au(60 nm)@SlO(2) core shell nanoparticles acting as plasmonic antennas. We observed high-quality, potential-dependent Raman spectra of the three viologen species V(2+),V(+center dot) and V(0) on a well-defined Au(111) substrate surface and could map their potential-dependent evolution. Comparison with experiments on powder samples revealed an enhancement factor of the nonresonant Raman modes of similar to 3 x 10(5), and up to 9 x 10(7) for the resonance modes. The study illustrates the unique capability of SHINERS and its potential in the entire field of electrochemical surface science to explore structures and reaction pathways on well-defined substrate surfaces, such as single crystals, for molecular, (electro-)- catalytic, bioelectrochemical systems up to fundamental double layer studies at electrified solid/liquid interfaces.

Comparison of performance and patient satisfaction of two types of ERG electrodes

BACKGROUND: An age-controlled comparison concerning patient satisfaction and electrical performance of microfibres (DTL) and rigid contact lens (Henkes) corneal ERG electrodes was carried out. METHODS: 36 test persons underwent complete ophthalmological examination and were equally distributed into 3 age groups. Electroretinograms were recorded according to ISCEV standards. Randomly, in one eye a Henkes electrode was used and in the other eye a DTL electrode. Amplitudes of a- and b-waves and implicit times were measured and compared for the two electrode types. RESULTS: 34 of 36 test persons preferred DTL electrodes. Electrical performance concerning b-wave amplitudes was comparable. Statistically significant differences were detected only for scotopic combined cone-rod stimulation in the age groups 20 - 40 and 41 - 60 years between the different electrodes. Other recordings did not show differences. A statistically significant reduction of signal amplitudes with age was detected for scotopic isolated rod signals and combined cone-rod signals. Significance level was p < 0.05. No conjunctival or corneal erosions were found after ERG recordings for either electrode. CONCLUSIONS: Electrical performance is comparable between electrodes. For scotopic stimulations age was a significant influencing factor for signal amplitude and should be respected for normative values. DTL electrodes were preferred by the vast majority of patients. No adverse clinical effects were observed for either electrode. DTL electrodes should be preferred due to hygienic reasons (single use) and patient comfort.

Electrochemical characterization of self-assembled Ferrocene-terminated alkanethiol monolayers on low-index gold single crystal electrodes

We present a voltammetric and in situ STM study of 11-ferrocenyl-1-undecanethiol (FcC11) assembled on low-index single crystal and polycrystalline gold electrodes. The influence of electrode surface structure as well as of structure defects in the self-assembled FcC11 monolayers on the electrochemical response during the oxidation and reduction of the terminal ferrocene group is explored. The nature of the redox peaks is discussed in detail. We identified the coexistence of disordered FcC11 regions with 2D patches of “locally ordered” FcC11 species. We demonstrate that close-packed domains are preferentially formed at atomically flat terraces. Increasing the defect density of the substrate surface leads to a decreasing amount of locally ordered FcC11 molecules.

Analysis of fractal electrodes for efficient neural stimulation

Planar electrodes are increasingly used in therapeutic neural stimulation techniques such as functional electrical stimulation, epidural spinal cord stimulation (ESCS), and cortical stimulation. Recently, optimized electrode geometries have been shown to increase the efficiency of neural stimulation by increasing the variation of current density on the electrode surface. In the present work, a new family of modified fractal electrode geometries is developed to enhance the efficiency of neural stimulation. It is shown that a promising approach in increasing the neural activation function is to increase the "edginess" of the electrode surface, a concept that is explained and quantified by fractal mathematics. Rigorous finite element simulations were performed to compute electric potential produced by proposed modified fractal geometries. The activation of 256 model axons positioned around the electrodes was then quantified, showing that modified fractal geometries required a 22% less input power while maintaining the same level of neural activation. Preliminary in vivo experiments investigating muscle evoked potentials due to median nerve stimulation showed encouraging results, supporting the feasibility of increasing neural stimulation efficiency using modified fractal geometries.