An apparatus for creating sheathed flow includes an inlet section comprising an array of tubes including at least one sheath inlet port and a sample inlet port, a flow focusing section downstream from the inlet section, an optical access section downstream from the flow focusing region and comprising opposing flat surfaces, and an outlet section downstream from the optical access section, wherein the apparatus is operable to create a sheathed flow around a fluid introduced into the sample inlet port and to maintain the sheathed flow through the optical access section. Applications of the apparatus and method include bead/particle counting, flow cytometry, waveguiding, and fluid control.
