Ciliary chemosensitivity is enhanced by cilium geometry and motility

Cilia are hairlike organelles with roles in motility and sensing. We investigate whether locating chemoreceptors on cilia provides sensitivity advantages and whether motile sensory cilia have further advantages. Using a simple advection-diffusion model, we compute capture rates of diffusive molecules to a cilium. We find that due to its geometry, a non-motile cilium in a quiescent fluid has a capture rate equal to that of a circular absorbing region with quadruple the surface area, and when the same cilium is exposed to an external shear flow, the equivalent surface area is sextuple that of the quiescent case. Alternatively, if the cilium beats in a non-reciprocal manner in an otherwise quiescent fluid, its capture rate increases with the beating frequency to the power of 1/3, and this motility advantage is seen to apply even in simulated cilium bundles. Altogether, our results show that the geometry of cilia provide one reason why many receptors are found on cilia and point to the advantage of combining motility with chemoreception, for a singular cilium as well as groups of cilia.