Miniature capsules shoot through water with the help of an unlikely power source — oxygen bubbles.
Inspired by the gas-filled organelles that some bacteria use, Pavan Kumar, Avinash Patil and Stephen Mann at the University of Bristol, UK, used DNA and clay to make ‘protocells’, rudimentary cell-like structures of 300–400 micrometres across. Each protocell contains an enzyme called catalase that converts hydrogen peroxide into oxygen and water.
When a protocell is exposed to hydrogen peroxide, the catalase generates one or more oxygen bubbles. Trapped inside the protocell, the bubbles grow larger and larger, providing buoyancy. A band of 225 protocells is strong enough to move a dialysis bag from the bottom of a container of water to the surface.
The team also made DNA protocells containing catalase and a second enzyme, glucose oxidase, that feeds on glucose. These protocells floated and sank repeatedly for five hours when they were alternately exposed to hydrogen peroxide and glucose.
Nature – Enzyme-powered motility in buoyant organoclay/DNA protocells
Reconstitution and simulation of cellular motility in microcompartmentalized colloidal objects have important implications for microcapsule-based remote sensing, environmentally induced signalling between artificial cell-like entities and programming spatial migration in synthetic protocell consortia. Here we describe the design and construction of catalase-containing organoclay/DNA semipermeable microcapsules, which in the presence of hydrogen peroxide exhibit enzyme-powered oxygen gas bubble-dependent buoyancy. We determine the optimum conditions for single and/or multiple bubble generation per microcapsule, monitor the protocell velocities and resilience, and use remote magnetic guidance to establish reversible changes in the buoyancy. Co-encapsulation of catalase and glucose oxidase is exploited to establish a spatiotemporal response to antagonistic bubble generation and depletion to produce protocells capable of sustained oscillatory vertical movement. We demonstrate that the motility of the microcapsules can be used for the flotation of macroscopic objects, self-sorting of mixed protocell communities and the delivery of a biocatalyst from an inert to chemically active environment. These results highlight new opportunities to constructing programmable microcompartmentalized colloids with buoyancy-derived motility.
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