Synthetic cells shed biological insights while delivering battery power

October 22, 2009

Trying to understand the complex workings of a biological cell by teasing out the function of every molecule within it is a daunting task. But by making synthetic cells that include just a few chemical processes, researchers can study cellular machinery one manageable piece at a time. A new paper* from researchers at Yale University and the National Institute of Standards and Technology (NIST) describes a highly simplified model cell that not only sheds light on the way certain real cells generate electric voltages, but also acts as a tiny battery that could offer a practical alternative to conventional solid-state energy-generating devices.

Each synthetic cell built by NIST engineer David LaVan and his colleagues has a droplet of a water-based solution containing a salt--potassium and chloride ions--enclosed within a wall made of a lipid, a molecule with one end that is attracted to water molecules while the other end repels them. When two of these "cells" come into contact, the water-repelling lipid ends that form their outsides touch, creating a stable double bilayer that separates the two cells' interiors, just as actual cell membranes do.

If the researchers only did that much, nothing interesting would happen, but they also inserted into the bilayer a modified form of a protein, alpha-hemolysin, made by the bacterium Staphylococcus aureus. These embedded proteins create pores that act as channels for ions, mimicking the pores in a biological cell. "This preferentially allows either positive or negative ions to pass through the bilayer and creates a voltage across it," LaVan says. "We can harness this voltage to generate electric current."

If the solutions in the two cells start with different salt concentrations, then poking thin metal electrodes into the droplets creates a small battery: electrons will flow through a circuit connected to the electrodes, counterbalancing the ion flow through the channels. As this happens, the ion concentrations in the droplets eventually equalize as the system discharges its electric potential.

Building synthetic versions of complex real cells--such as those that enable an electric eel to zap its prey--is far too difficult a task for now, says LaVan. So the researchers instead created this far simpler system whose performance they could understand in terms a handful of basic properties, including the size of the droplets, the concentration of the aqueous solutions, and the number of ion channels in the barrier between the two cells.

A tiny battery with two droplets, each containing just 200 nanoliters of solution, could deliver electricity for almost 10 minutes. A bigger system, with a total volume of almost 11 microliters, lasted more than four hours. In terms of the energy it can deliver for a given volume, the biological battery is only about one-twentieth as effective as a conventional lead-acid battery. But in its ability to convert chemical into electrical energy, the synthetic cell has an efficiency of about 10 per cent, which compares well with solid-state devices that generate electricity from heat, light, or mechanical stress--so that synthetic cells may one day take their place in the nanotechnology toolbox.
-end-
*J. Xu, F.J. Sigworth, and D.A. LaVan. Synthetic Protocells to Mimic and Test Cell Function. Advanced Materials, published online Oct. 1, 2009

National Institute of Standards and Technology (NIST)

Related Droplets Articles from Brightsurf:

Valves on N95 masks do not filter exhaled droplets
Matthew Staymates, fluid dynamicist at the National Institute of Standards and Technology, is studying different mask types to determine which are the most effective at reducing disease transmission.

Water predictions: Telling when a nanolithography mold will break through droplets
Ultraviolet nanoimprint lithography is powerful method of producing polymer nanostructures by pressing a curable resin onto a mold.

Tracking flight trajectory of evaporating cough droplets
The ongoing COVID-19 pandemic has led many to study airborne droplet transmission in different conditions and environments, and in Physics of Fluids, researchers from A*STAR conducted a numerical study on droplet dispersion using high fidelity air flow simulation.

Aerosols vs droplets
Winter is on its way. And in this year of coronavirus, with it comes the potential for a second wave of COVID-19.

How everyday speech could transmit viral droplets
High-speed imaging of an individual producing common speech sounds shows that the sudden burst of airflow produced from the articulation of consonants like /p/ or /b/ carry salivary and mucus droplets for at least a meter in front of a speaker.

Conversation quickly spreads droplets inside buildings
With implications for the transmission of diseases like COVID-19, researchers have found that ordinary conversation creates a conical 'jet-like' airflow that quickly carries a spray of tiny droplets from a speaker's mouth across meters of an interior space.

Plant droplets serve as nutrient-rich food for insects
Small watery droplets on the edges of blueberry bush leaves are loaded with nutrients for many insects, including bees, wasps and flies, according to a Rutgers-led study, the first of its kind.

Mysterious cellular droplets come into focus
Researchers are shedding light on a type of membrane-less organelle, known as biological condensates, that play a role in DNA repair and aging.

Physics -- Bubbling and burping droplets of DNA
Liquid droplets formed from DNA display a peculiar response to enzymes.

Levitating droplets allow scientists to perform 'touchless' chemical reactions
Levitation has long been a staple of magic tricks and movies.

Read More: Droplets News and Droplets Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.