In our continuing coverage of Things-That-Move (Making-It-Move) see previous episode, we have a first contestant with an actual usability claim! Carbon dioxide sequestration no-less. In a recent Angewandte Uygun et al. (DOI) describe so-called microscrubbers that in the near-future should patrol the oceans scrubbing it of CO2. Here is how it works.
Nature's way to get rid of carbon dioxide is to convert it to solid calcium carbonate. This is what happens in the planet's oceans but only slowly. The enzyme carbonic anhydrase (CA) is able to catalyse the hydration of carbon dioxide, which happens to be the rate-limiting step. But the enzyme on it's own is too unstable and still too slow. In the new microscrubber the enzyme is attached to a micromotor. It gives the enzyme stability and because the solid support moves around it's efficiency is improved by a combination of self-mixing, convection and inhibition of sedimentation.
The micromotor construction manual describes the following steps: take a polycarbonate membrane with 5 micrometer conical shaped micropores, sputter gold on one side, electropolymerize a polypyrrole-COOH/PEDOT inner layer, then add a platinum layer by electrodeposition, then remove the gold layer by hand polishing and then dissolve membrane in methylene chloride to release the microtubes. Then link the terminal carboxylic acid groups on the surface of the microtubes to CA enzyme using ENSI and N-Hydroxysuccinimide NHS as coupling agents.
The swimming arena is plain seawater but with hydrogen peroxide and sodium cholate added for micromotor propulsion. And the results? The microtubes can be observed swirling around while pooping out solid clumps of calcium carbonate. Average speed: 100 micrometer per second, payload 600 microgram of CA per three million microtubes and 90% yield in just 5 minutes.
In their conclusion the authors have promised that their next-generation scrubber would have the peroxide fuel replaced with something more realistic.