The physics of capillary-driven liquid handling in SPOTs microdroplet arrays

Microdroplet arrays allow efficient manipulation of many independent experiments. We recently introduced Surface Patterned Omniphobic Tiles (SPOTs), a microdroplet array platform that uses patterned omniphobic surfaces and carefully engineered loading devices to precisely and rapidly manipulate hundreds to thousands of independent reactions in parallel. Here we explore the physics underpinning liquid handling by the system. We present experimental and theoretical arguments that elucidate how capillarity and geometry determine the metered volumes, and we show the relative importance of surface tension, viscosity, device geometry, and loading speed in liquid handling performance. We conclude by highlighting use cases of the platform for combinatorial experiments in fluid-phase experiments across chemistry, biology, and material science.