We report the collision behavior of single unilamellar vesicles, composed of a bilayer lipid membrane (BLM), on a platinum (Pt) ultramicroelectrode (UME) by two electrochemical detection methods. In the first method, the blocking of a solution redox reaction, induced by the single vesicle adsorption on the Pt UME, can be observed in the amperometric i-t response as current steps during the electrochemical oxidation of ferrocyanide. In the second technique, the ferrocyanide redox probe is directly encapsulated inside vesicles and can be oxidized during the vesicle collision on the UME if the potential is poised positive enough for ferrocyanide oxidation to occur. In the amperometric i-t response for the latter experiment, a current spike is observed. Here, we report the vesicle blocking (VB) method as a relevant technique for determining the vesicle solution concentration from the collisional frequency and also for observing the vesicle adhesion on the Pt surface. In addition, vesicle reactor (VR) experiments show clear evidence that the lipid bilayer membrane does not collapse or break open at the Pt UME during the vesicle collision. Because the bilayer is too thick for electron tunneling to occur readily, an appropriate concentration of a surfactant, such as Triton X-100 (TX100), was added in the VR solution to induce loosening of the bilayer (transfection conditions), allowing the electrode to oxidize the contents of the vesicle. With this technique, the TX100 effect on the vesicle lipid bilayer permeability can be evaluated through the current spike charge and frequency corresponding to redox vesicle collisions.

The present study aims to get more insight into the role of pyridinium ions, surface H atoms and the nature of the electrode surface for the electrochemical reduction of CO2. The electrochemical activity of pyridinium ions in the absence and presence of CO2 is investigated on Ir, Pt, Au and glassy carbon electrodes. Glassy carbon and Au electrodes show irreversible reduction of pyridinium characterized by a cathodic peak potential. In the further presence of CO2, an increase of the current is noticed and the overall reduction process remains irreversible. In contrast, cyclic voltammograms recorded on an Ir electrode in a pyridine solution under nitrogen and CO2 are quasi‐reversible and consistent with the participation of H atoms adsorbed onto the electrode surface. Cyclic voltammograms for Ir and Pt electrodes are similar, as expected for metals with a strong affinity for hydrogen. Our results suggest that adsorbed H atoms may play a key role in the electrochemical reduction of CO2.

The electrochemical detection of synthetic redox DMPC (1,2-dimyristoyl-sn-glycero-3phosphocholine) liposomes by single collisions at 10 µm diameter carbon and Pt ultramicroelectrodes (UMEs) is reported. To study the parameters influencing the lipid membrane opening/permeability, the electrochemical detection of single redox DMPC liposome collisions at polarized UMEs was investigated under different experimental conditions (addition of surfactant, temperature). The electrochemical responses recorded showed that the permeability of the DMPC lipid membrane (tuned by addition of Triton X-100 surfactant or by the increase of the solution temperature) is a key parameter for the liposome membrane electroporation process and hence for the release and oxidation of its redox content during the collision onto UMEs. The presence of ferrocenemethanol as an additional redox probe in the aqueous solution (at room temperature and without addition of surfactant) is also an interesting strategy to detect current spikes corresponding to single redox DMPC liposome collisions with K 3 Fe(CN) 6 /K 4 Fe(CN) 6 as the encapsulated aqueous redox probe.