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Stokes trap for multiplexed particle manipulation and assembly using fluidics

Significance In recent years, techniques for trapping and manipulating small particles and single molecules have catalyzed major advances in several fields of science. Here, we describe a new method for confining, manipulating, and assembling multiple particles in free solution using the sole action of fluid flow. The Stokes trap provides a fundamentally new method for particle manipulation and assembly using a simple microfluidic device and nonlinear feedback control in the absence of optical, electric, or magnetic fields. This method holds strong potential to enable fundamental studies in soft materials, colloidal science, and biophysics. The ability to confine and manipulate single particles and molecules has revolutionized several fields of science. Hydrodynamic trapping offers an attractive method for particle manipulation in free solution without the need for optical, electric, acoustic, or magnetic fields. Here, we develop and demonstrate the Stokes trap, which is a new method for trapping multiple particles using only fluid flow. We demonstrate simultaneous manipulation of two particles in a simple microfluidic device using model predictive control. We further show that this approach can be used for fluidic-directed assembly of multiple particles in solution. Overall, this technique opens new vistas for fundamental studies of particle–particle interactions and provides a new method for the directed assembly of colloidal particles.