PubMed · 6352363
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J L Stirling, H P Bennetto, G M Delaney, J R Mason, S D Roller, K Tanaka, C F Thurston. 1983. Microbial fuel cells.. https://doi.org/10.1042/bst0110451
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The influence of the spontaneous surface modification of titanium by exposure to Ringer's solution at open-circuit conditions on the passive behavior was studied. The electrochemical behavior of Ti was compared in a simple NaCl and in Ringer's physiological solution. Potentiodynamic polarization curves show significantly higher passive current densities in Ringer's solution as compared with the simple saline solution. Furthermore, impedance spectra measured at the open-circuit potential as a function of time indicate that in saline solution a long-term exposure over some days leads to a strong increase of the protectiveness of the passive film. This improvement of the passive behavior cannot be observed in Ringer's solution, but a strong modification of the passive film/electrolyte interface can be seen in the impedance spectra. The changes in the impedance spectra can be correlated with the results observed by surface characterization regarding the morphology (scanning electron microscopy) and chemical composition of the surface (X-ray photoelectron spectroscopy). In agreement with previous work by others, a spontaneous modification of the surface of Ti by Ca and P species was observed. The composition of the Ca/P precipitates changes as a function of time, indicating a slow formation of a hydroxyapatite-like deposit layer on the surface. The results of the present work indicate that the formation of the outer Ca-P deposit layer on the passive Ti surface (which is beneficial for the biological performance) hinders the normal aging of the passive TiO(2). Even though the protectiveness of the passive film can be considered as high also in Ringer's solution, significantly higher passive dissolution rates (i.e., higher metal-ion release) for Ti exposed to Ringer's solution can be expected as compared with a simple saline solution.
Electrocatalytic processes can take place either homogeneously in a single liquid phase or heterogeneously at the liquid-liquid interface formed in emulsions. This Article addresses the question as to whether a change in rate and/or mechanism can occur between the two possibilities. Specifically, cyclic voltammetry and electrosynthetic experiments are used to demonstrate that for the vitamin B12 mediated reduction of vicinal dibromides producing olefins, electric field effects likely operate at the liquid-liquid interface which can change the populations of different conformers relative to the single homogeneous-phase experiment, leading to significant changes in rate.
We report the fabrication and characterization of a micropatterned membrane electrode for electrochemical signaling of a bacterial pore-forming toxin, Streptolysin O (SLO) from S. pyogenes. Microcontact printing of an alkylthiol monolayer was used to fabricate an array template, onto which cholesterol-containing DMPC vesicles were fused to form lipid layer structures. The construction of the supported membranes, including pattern transfer and vesicle fusion, was characterized by in-situ surface plasmon resonance (SPR) imaging and electrochemistry. Quantitative analysis of the resulting membrane by using SPR angular shift measurements indicates that the membranes in the hydrophilic pockets have an average thickness of 8.2 +/- 0.4 nm. Together with fluorescence microscopy studies, the results suggest that this could be a mixed lipid assembly that may consist of a bilayer, vesicle fragments, and lipid junctions. The voltammetric response of the redox probe ferrocene carboxylic acid (FCA) was measured to quantify the toxin action on the supported membrane. The electrochemical measurements indicate that fusion of vesicles on the template blocked the access of FCA, whereas the injection of SLO toxin restored the redox response. The anodic peak current of FCA was found to increase with toxin concentration until a plateau was reached at 40 HU/mL. The method is highly sensitive such that 0.1 HU/mL of SLO (1.25 pM) can yield a well-defined response. In addition, it eliminates the need for a highly insulating layer in membrane sensing, which opens up new avenues in developing novel sensing interfaces for membrane-targeting proteins and peptides.