The Chemotactic Droplet

19 February 2010 - Making It Move II



This blog has a longstanding interest in a peculiar branch of chemistry dedicated to making small objects physically move in response to chemicals in their environment (synthetic chemotaxis), previous episodes here and here. In their latest entry Lagzi et al. (DOI) (inspired by Hanczyc et al. DOI 2007 is not recent!) have come up with a practical solution to a nonexistent problem how to send a droplet of oil through a maze using the shortest possible path.

A PDMS maze was constructed with channels 1 mm wide and filled with a KOH solution. One entrance was filled with agarose soaked in a HCl solution and the other entrance was the starting point for a droplet of oil (mineral oil/2-hexyldecanoic acid). In this system the droplet moves along a gradient of lower pH (1 mm/s). The fatty acid component in the oil drop diffuses into the water more rapidly facing the region with lower pH due to protonation, resulting in a surface tension gradient fuelling the motion.

The concept needs refining but this blog is confident that in the future it is be possible to toss oil into the ocean somewhere in the Middle East and collect it again close to shore anywhere in Europe without having to bother with oil tankers.