The team, from Yale University and the National Institute of Standards and Technology (NIST), have developed a highly simplified model cell that includes only a few chemical processes which reproduce cell function, to help them understand how real cells can generate electric voltages and act as tiny batteries. This research shows how such cells could provide an alternative to conventional solid-state energy-generating devices and other new energy technologies.

Published online in [Xu et al., Advanced Materials, doi: 10.1002/adma.200901945], the methodology used allows the study of cellular machinery in terms of some basic properties, such as the size of the droplets, the concentration of the aqueous solutions and the number of ion channels in the barrier between the two cells, simplifying the process of examining how biological cells work, and enabling them to examine biological energy conversion processes.

The study found that a tiny battery with two droplets, each containing just 200 nanoliters of solution, could deliver electricity for almost 10 minutes, while a bigger system, with a total volume of almost 11 microliters, lasted more than four hours. Although the biological battery is not as effective as a conventional lead-acid battery, it is efficient in terms of its ability to convert chemical into electrical energy.

The synthetic cells have a droplet of a water-based solution containing a salt – potassium and chloride ions – enclosed within a lipid wall, a molecule with one end that is attracted to water molecules while the other end repels them. If the solutions in the two cells start with different salt concentrations, then poking thin metal electrodes into the droplets creates a small electric battery.

They then inserted into the bilayer a modified form of a protein, alpha-hemolysin, which create pores that act as channels for ions, mimicking the pores in a biological cell. As David LaVan points out, “This preferentially allows either positive or negative ions to pass through the bilayer and creates a voltage across it. We can harness this voltage to generate electric current.”

The study has effectively demonstrated that synthetic cells can be a key method for making cell measurements, and a means to isolate and study individual components in cell systems.