An integrated flow-cell for full sample stream control

In this study, we present a novel three-dimensional hydrodynamic sheath flow chip that allows full control of a sample stream. The chip offers the possibility to steer each of the four side sheath flows individually. The design of the flow-cell exhibits high flexibility in creating different sample stream profiles (width and height) and allows navigation of the sample stream to every desired position inside the microchannel (vertical and horizontal). This can be used to bring the sample stream to a sensing area for analysis, or to an area of actuation (e.g. for cell sorting). In addition, we studied the creation of very small sample stream diameters. In microchannels (typically 25 × 40 μm2), we created sample stream diameters that were five to ten times smaller than the channel dimensions, and the smallest measured sample stream width was 1.5 μm. Typical flow rates are 0.5 μl/min for the sample flow and around 100 μl/min for the cumulated sheath flows. The planar microfabricated chip, consisting of a silicon–glass sandwich with an intermediate SU-8 layer, is much smaller (6 × 9 mm2) than the previously presented sheath flow devices, which makes it also cost-effective. We present the chip design, fluidic simulation results and experiments, where the size, shape and position of the sample stream have been established by laser scanning confocal microscopy and dye intensity analysis.