Multilayer hydrodynamic sheath flow structure

1. A sheath flow structure for suspending a particle in a sheath fluid, comprising:

a first substrate layer including a primary sheath flow channel for conveying the sheath fluid;

a second substrate layer stacked on the first substrate layer including a first sheath inlet for introducing the sheath fluid to the primary sheath flow channel, and a sample inlet downstream of the first sheath inlet for providing the particle to the primary sheath flow channel in a primary focusing region to form a sheath flow including the particle surrounded by the sheath fluid on at least one side; and

a first secondary sheath channel formed in one of said first substrate layer and said second substrate layer in communication with the primary sheath flow channel, wherein the first secondary sheath channel diverts a portion of the sheath fluid from the primary sheath flow channel.

2. The sheath flow structure of claim 1 , wherein the first secondary sheath channel intersects the primary sheath flow channel in a region between said first sheath inlet and said sample inlet.

3. The sheath flow structure of claim 1 , wherein the first secondary sheath channel provides the diverted portion of the sheath fluid to a secondary focusing region downstream of the primary focusing region, where the diverted portion of the sheath fluid reenters the primary sheath flow channel to focus the particle within the sheath flow.

4. The sheath flow structure of claim 1 , wherein the first secondary sheath channel is formed in the second substrate layer.

5. The sheath flow structure of claim 1 , further comprising a second secondary sheath channel for diverting another portion of said sheath fluid from the primary sheath flow channel, the first secondary sheath channel provided on a first side of the primary sheath flow channel and the second secondary sheath channel provided on a second side of the primary sheath flow channel.

6. The sheath flow structure of claim 1 , further comprising a secondary focusing region for focusing the sheath flow around the particle.

7. The sheath flow structure of claim 1 , wherein the primary focusing region is formed by tapering the primary sheath flow channel in a direction along which fluid flows therethrough.

8. The sheath flow structure of claim 7 , wherein the sample inlet intersects a relatively wide portion (W) of the primary sheath flow channel.

9. The sheath flow structure of claim 1 , wherein the primary sheath flow channel divides into a first subchannel and a second subchannel upstream of the primary focusing region.

10. The sheath flow structure of claim 9 , wherein the first subchannel and the second subchannel converge in the primary focusing region to surround the particle provided in the primary focusing region with the sheath fluid.

11. The sheath flow structure of claim 1 , wherein the primary sheath flow channel is a microchannel.

12. The sheath flow structure of claim 1 , wherein the sheath flow structure is a microfluidic device.

13. A method of surrounding a particle on at least two sides by a sheath fluid, comprising the steps of:

injecting a sheath fluid into a primary sheath flow channel;

diverting a portion of the sheath fluid into a branching sheath channel;

injecting the particle into the primary sheath flow channel to suspend the particle in the sheath fluid to form a sheath flow; and

injecting the diverted portion of the sheath fluid into the sheath flow to focus the particle within the sheath fluid.

14. A method of surrounding a particle on at least two sides by a sheath fluid, comprising the steps of:

conveying the sheath fluid through a primary sheath flow channel;

injecting the particle into the sheath fluid conveyed through the primary sheath flow channel;

focusing the sheath fluid around the particle in at least a first direction; and

focusing the sheath fluid around the particle in at least a second direction different from the first direction.