Microdroplet Reactors Mimic Living Systems
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Institute has used microdroplets to study non-equilibrium reactions like those in living organisms.
“Living systems are achieved by complex chemical reaction dynamics far from equilibrium, such as gene expression networks, signalling networks, metabolic circuits and neural networks,” explain Masahiro Takinoue at Tokyo Institute of Technology and his colleagues. The researchers now demonstrate that their microdroplet system can offer the control over chemical fluxes needed to keep this kind of reaction far from equilibrium.
Takinoue and his colleagues used a microfluidic system containing a droplet of water in oil with electrodes either side as the chemical reaction site. They then passed a train of water-in-oil droplets past the reactor droplet. As each droplet passed the reactor droplet, applying an A.C. voltage across the electrodes led to fusion, allowing chemical exchange. The shear force of the droplet train then caused fission, leaving the reactor droplet self-contained until voltage-induced fusion with the following droplet.
The research team mathematically modelled how by switching the A.C. voltage on and off they could control the fusion/fission timing, and hence the chemical flux and reaction dynamics. As a model system, they then produced a microdroplet system of bromite (BrO3-), sulphite (SO32-) and ferrocyanide (Fe(CN)64-). The pH in the droplet oscillates as hydrogen cations are produced and consumed through autocatalytic reactions. Using pH-sensitive fluorescent molecules, the researchers could monitor these reaction dynamics and incorporate feedback.
“Complicated microfluidic components, such as valves and mixers, are unnecessary,” point out the researchers, as the a.c. voltage pulse-modulated reactor provides chemical flux control. In addition the fast fusion response to the applied electric field allows a range of waveforms of the droplet train density to be studied, including sinusoidal, square and saw tooth. As a result it could provide a powerful tool for studying synthetic biology to understand life, as well as bio-inspired self-controlling and dynamic systems.
