In situ electrochemistry inside a TEM with controlled mass transport.

The field of electrochemistry promises solutions for the future energy crisis and environmental deterioration by developing optimized batteries, fuel-cells and catalysts. Combined with in situ transmission electron microscopy (TEM), it can reveal functional and structural changes. A drawback of this relatively young field is lack of reproducibility in controlling the liquid environment while retaining the imaging and analytical capabilities. Here, a platform for in situ electrochemical studies inside a TEM with a pressure-driven flow is presented, with the capability to control the flow direction and to ensure the liquid will always pass through the region of interest. As a result, the system offers the opportunity to define the mass transport and control the electric potential, giving access to the full kinetics of the redox reaction. In order to show the benefits of the system, copper dendrites are electrodeposited and show reliable electric potential control. Next, their morphology is changed by tuning the mass transport conditions. Finally, at a liquid thickness of approximately 100 nm, the diffraction pattern revealed the 1,1,1 planes of the copper crystals, indicating an atomic resolution down to 2.15 Å. Such control of the liquid thickness enabled elemental mapping, allowing us to distinguish the spatial distribution of different elements in liquid.

In situ modification of plain liposomes with lipidated coiled coil forming peptides induces membrane fusion.

Complementary coiled coil forming lipidated peptides embedded in liposomal membranes are able to induce rapid, controlled, and targeted membrane fusion. Traditionally, such fusogenic liposomes are prepared by mixing lipids and lipidated peptides in organic solvent (e.g., chloroform). Here we prepared fusogenic liposomes in situ, i.e., by addition of a lipidated peptide solution to plain liposomes. As the lipid anchor is vital for the correct insertion of lipidated peptides into liposomal membranes, a small library of lipidated coiled coil forming peptides was designed in which the lipid structure was varied. The fusogenicity was screened using lipid and content mixing assays showing that cholesterol modified coiled coil peptides induced the most efficient fusion of membranes. Importantly, both lipid and content mixing experiments demonstrated that the in situ modification of plain liposomes with the cholesterol modified peptides yielded highly fusogenic liposomes. This work shows that existing membranes can be activated with lipidated coiled coil forming peptides, which might lead to highly potent applications such as the fusion of liposomes with cells.