Simple Theory for Binding-Based Molecular Chemotaxis

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We simulated a three-inlet one-outlet microfluidic channel of width 360 µm used in chemotaxis experiments. To determine the distribution of probe and ligand molecules at the bottom of the channel, we solved the Fokker-Planck equation and generated the horizontal concentration profiles after 15 s of simulation time. To quantify the chemotactic shift of the probe, we normalized the profiles for the “experiment” and a control, calculated the average position of probe along the horizontal axis, and took the difference between the two. We predicted directional motion for a probe molecule with two binding sites and noted a significant increase in the chemotactic shift as the binding constant for the second binding event increased. The chemotactic effect is also enhanced if binding to a ligand molecule raises the effective diffusivity of the probe. This work is significant in informing the design of new chemical and biochemical devices that can make use of these chemotactic effects to control the motion of molecules at the nanoscale.

Kathleen T. Krist and William G. Noid Department of Chemistry, Pennsylvania State University


MRSEC researchers have developed a theory for molecular chemotaxis, active motion up or down a gradient in chemical concentration, driven by specific non-covalent interactions between molecules. The free energy released due to binding between a probe P and a ligand L generates a force that drives the two species towards each other. The magnitude of the chemotactic shift μP depends on the binding strength and the diffusivity of the probe-ligand complex. Insights from this theory can guide development of chemotaxis-based devices that sort and separate fluids components actively and against diffusional gradients.

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IRG2 - Nanomotors