Macroscopic Convective Fluid Flows Arising From Binding of Ions and Small Molecules to Proteins

Chemically-powered autonomous fluid flow provides a model platform for investigating active matter at the molecular scale and has promising biochemical applications. Although catalysis-driven convective flows have been extensively investigated, the physical mechanisms by which proteins can induce transport through simple molecular binding remain poorly understood. Here, ligand and metal ion binding to immobilized proteins is demonstrated to be sufficient to initiate and sustain macroscopic convective fluid flow. A physical model is proposed in which nickel binding and the release of structured water molecules from the protein's hydration shell into the bulk solution generate local density variations. Using a combination of experimental measurements and computational modeling, the coupling between buoyancy- and diffusion-driven transport mechanisms that gives rise to sustained and directional flow patterns is examined. The results illustrate that the protein-based pumps exhibit high selectivity, enabling discrimination of specific metal ions, such as nickel, from complex mixtures. Beyond its relevance to active matter, the proposed mechanism can be used in flow-based sensing and bioresponsive devices that transform binding events into observable fluid motion.