A microfluidic assembly for use with a particle processing system comprising: a substantially planar substrate having upper and lower surfaces; and a microfluidic flow channel formed in the substrate, the microfluidic flow channel having: an inlet configured to receive a sample stream; characterized by a fluid focusing region (530, 630, 730) having a fluid focusing chamber (520, 620, 720) including a core stream forming geometry (500, 600, 700) configured to focus the sample stream, the core stream forming geometry having a lateral fluid focusing region (532, 632, 732) and having a first pair of vertical fluid focusing channels (540a, 540b, 640a, 640b, 740a, 740b) and a second pair of vertical fluid focusing channels (550a, 550b, 650a, 650b,750a, 750b) configured to introduce opposing vertical fluid focusing sheath flows into the lateral fluid focusing chamber (520, 620, 720) for an improved core stream formation, the first pair of vertical fluid focusing channels introduces focusing fluid into a downstream end (520b, 620b, 720b) of the fluid focusing chamber (520, 620, 720) at a first vertical focusing flow inlet (548, 648, 748) from above, the second pair of vertical fluid focusing channels introduces focusing fluid into the downstream end (520b, 620b, 720b) of the fluid focusing chamber at a second vertical focusing flow inlet (546, 646, 746) from below such that after being laterally focused, the stream is vertically focused downward and then vertically focused upward; and an inspection region at least partially downstream of the fluid focusing region. a substantially planar substrate having upper and lower surfaces; and a microfluidic flow channel formed in the substrate, the microfluidic flow channel having: an inlet configured to receive a sample stream; characterized by a fluid focusing region (530, 630, 730) having a fluid focusing chamber (520, 620, 720) including a core stream forming geometry (500, 600, 700) configured to focus the sample stream, the core stream forming geometry having a lateral fluid focusing region (532, 632, 732) and having a first pair of vertical fluid focusing channels (540a, 540b, 640a, 640b, 740a, 740b) and a second pair of vertical fluid focusing channels (550a, 550b, 650a, 650b,750a, 750b) configured to introduce opposing vertical fluid focusing sheath flows into the lateral fluid focusing chamber (520, 620, 720) for an improved core stream formation, the first pair of vertical fluid focusing channels introduces focusing fluid into a downstream end (520b, 620b, 720b) of the fluid focusing chamber (520, 620, 720) at a first vertical focusing flow inlet (548, 648, 748) from above, the second pair of vertical fluid focusing channels introduces focusing fluid into the downstream end (520b, 620b, 720b) of the fluid focusing chamber at a second vertical focusing flow inlet (546, 646, 746) from below such that after being laterally focused, the stream is vertically focused downward and then vertically focused upward; and an inlet configured to receive a sample stream; characterized by a fluid focusing region (530, 630, 730) having a fluid focusing chamber (520, 620, 720) including a core stream forming geometry (500, 600, 700) configured to focus the sample stream, the core stream forming geometry having a lateral fluid focusing region (532, 632, 732) and having a first pair of vertical fluid focusing channels (540a, 540b, 640a, 640b, 740a, 740b) and a second pair of vertical fluid focusing channels (550a, 550b, 650a, 650b,750a, 750b) configured to introduce opposing vertical fluid focusing sheath flows into the lateral fluid focusing chamber (520, 620, 720) for an improved core stream formation, the first pair of vertical fluid focusing channels introduces focusing fluid into a downstream end (520b, 620b, 720b) of the fluid focusing chamber (520, 620, 720) at a first vertical focusing flow inlet (548, 648, 748) from above, the second pair of vertical fluid focusing channels introduces focusing fluid into the downstream end (520b, 620b, 720b) of the fluid focusing chamber at a second vertical focusing flow inlet (546, 646, 746) from below such that after being laterally focused, the stream is vertically focused downward and then vertically focused upward; and an inspection region at least partially downstream of the fluid focusing region.