A Biohybrid Microfluidic Valve Based on Forisome Protein Complexes

Externally adjustable and reversibly switchable valves are key actuators in microchannels. A related function is required for full fluidic control over the flow in the vascular microchannels (phloem) of plants. Evolution fulfilled this in the Fabaceae family through using reversibly swellable protein aggregates (forisomes). The swelling behavior is regulated in the vessels by calcium but is also pH dependent. In order to utilize the natural forisome elements in a technical chip application, we integrated the protein complexes into the channel system of a microflow cell. In this artificial environment, the reversible conformation change of the forisomes could be induced by varying the calcium concentration or by an electrically generated pH shift. In consequence, the swelling of the forisome reversibly blocked a microparticle flow in various branched and unbranched channel geometries. The regulation of the flow was successfully verified by detecting the particle flux while switching the valve and by impedance spectroscopy. In conclusion, forisome plant protein bodies are a valve element that can readily be integrated into microfluidics and can also be externally controlled to selectively retain objects that pass the channel.