Powering droplet networks

Lipid bilayers, either between two droplets or between a droplet and hydrogel surface, are a useful tool for studying membrane proteins in a natural environment. These droplet - hydrogel bilayers have been used previously as a synthetic retina, where a protein called bacteriorhodopsin generated a photocurrent across a membrane upon activation by a light source which was processed and used to make a greyscale image of and object above the retina. Recently there have been remarkable advancements in this field, with a 3D droplet printer having been developed in the Bayley group which allows for the rapid printing of huge droplet networks as a tissue mimic. These can be functionalised with ion pores, enabling a current to be carried through a predetermined pattern which can then be seen as a simplistic synthetic nerve. One challenge still to be overcome in these systems is the powering of droplet networks. The project I will be working on will be just this, by utilising F1F0 ATP synthase and establishing a proton gradient, via a rhodopsin, across a lipid bilayer to create an artificial chloroplast able to power neighbouring droplets via the molecule ATP. As seen in the mitochondria, a high surface area will be needed to ensure efficient ATP synthesis, and so many lipid vesicles (measuring in the tens of nanometres in diameter) inside the droplet will be used as the scaffold to hold the two proteins. Reconstitution of the two proteins will be the one challenge, to ensure their orientation is correct, however there has been work performed previously on this. Production of ATP can be quantified either with a Luciferase assay or via the production of a fluorescent product in an ATP dependent enzymatic pathway. This energy source can be used to power active transporters for cations, resulting in a unidirectional flow of cations leading to a build of charge. This charge can be seen as a storage of energy that can be utilised at a later time. ATP also induce the production of proteins in cells, and so could be utilised in our droplet networks to induce production of proteins on demand. These proteins could have therapeutic effects or perform transformations on small molecules. While powering a droplet is one goal of this project, the main objective and novelty of the research will come from combining these "powered" droplets with the 3D droplet printer developed in the Bayley group to build functionalised networks of droplets that can respond to an external stimulus (light). This can be either through ATP transporters or via the flow of ions described previously. The biocompatibility of droplet networks is a major advantage associated with this technology. Once droplets networks have been sufficiently functionalised by both membrane proteins and cytosolic proteins one could very reasonably expect that these networks could be used in a surgical situation. For example, as a biocompatible recording device, to monitor and report the concentrations of molecules in the blood, or as a drug delivery system that is activated by light at a specific location. This project falls within the EPSRC Chemical Biology research area.