Hydrodynamic Trap Array. The array includes a serpentine bypassing channel including a plurality of trapping pockets disposed therein, the trapping pockets including a ramp entry portion to decrease flow velocity orthogonal to the trapping pocket to increase trapping efficiency. The relative fluid resistances of the trapping pockets and the serpentine bypassing channel are selected such that a slight majority of the flow is diverted to one of the trapping pockets. A pair of microfluidic bypass channels flank the array of traps allowing independent control of upstream and downstream pressures on each side of the array, thereby decoupling flow magnitude in the bypass channels from flow across the trapping pockets.