Systems and methods for particle focusing in microchannels

1. A system for focusing particles suspended within a moving fluid, the system comprising:

a substrate;

at least one channel provided on the substrate, the at least one channel having an inlet, an outlet, a plurality of sides, wherein the relative geometry of the sides defines an aspect ratio, and a channel hydraulic diameter (D h ), wherein the at least one channel is configured to allow a fluid having a substantially constant kinematic viscosity (v) that includes suspended particles, each having a particle diameter (a), to flow therethrough; and

a pumping element designed to drive the fluid that includes the suspended particles through the at least one channel;

wherein when the fluid that includes the suspended particles is flowed through the at least one channel, and the pumping element drives the fluid that includes the suspended particles at a maximum channel velocity (U m ) resulting in a laminar fluid flow and a particle Reynolds Number (R p )) of greater than or equal to 0.2, wherein the particle Reynolds number is defined as

R

p

=

U

m

⁢

a

2

⁢

vD

h

,

one or more localized stream lines are formed in the fluid, wherein each localized stream line defines a width that is substantially equal to or greater than a size of the focused particles, and the particles suspended in the fluid are focused into the one or more localized stream lines, wherein the number and relative cross-sectional position of the one or more localized stream lines are uniquely defined by the aspect ratio and the particle Reynolds number.

2. The system of claim 1 , wherein the at least one channel has a width and a height that define the aspect ratio of the at least one channel, and wherein when the aspect ratio of the at least one channel is substantially 1 to 1, the particles suspended in the fluid are focused into four localized stream lines.

3. The system of claim 1 , wherein the at least one channel has a width and a height that define the aspect ratio of the at least one channel, and wherein when the aspect ratio of the at least one channel is substantially 2 to 1, the particles suspended in the fluid are focused into two localized stream lines.

4. The system of claim 1 , wherein the at least one channel is a straight channel, and the particles suspended in the fluid are focused into each of at least two localized stream lines.

5. The system of claim 1 , wherein a ratio of the particle diameter to the at least one channel hydraulic diameter is greater than or equal to about 0.07.

6. The system of claim 5 , wherein the ratio of the particle diameter to the at least one channel hydraulic diameter is less than or equal to about 0.5.

7. The system of claim 1 , wherein the width defined by each localized stream line is about 1.05 times the particle diameter.

8. The system of claim 1 , wherein the width defined by each localized stream line is about five times the particle diameter.

9. The system of claim 1 , wherein at least first and second outlet branches are formed at an outlet portion of the at least one channel, at least one of the first and second outlet branches being located so as to receive the particles that are focused into a localized stream line.

10. The system of claim 9 , wherein each of the at least first and second outlet branches are formed such that a concentration of the particles suspended in the fluid flowing through the at least one of the first and second outlet branches is greater than a concentration of the particles suspended in the fluid entering the inlet of the at least one channel.

11. The system of claim 1 , wherein the at least one channel is formed to focus particles having a particle diameter in a range of 0.01 μm to 40 μm.

12. The system of claim 1 , wherein when the fluid that includes the suspended particles is flowed through the at least one channel, and the pumping element drives the fluid that includes the suspended particles at a particle Reynolds Number (R p ) of greater than or equal to 0.2, the focused particles are spaced within a localized stream line approximately evenly longitudinally.

13. The system of claim 1 , wherein the at least one channel has a width and a height that defines the aspect ratio of the at least one channel, and wherein the aspect ratio is 1 at or substantially near the inlet and varies over the length of the at least one channel to 2 at or substantially near the outlet.

14. The system of claim 4 , further comprising a curved channel connected to the outlet of the at least one channel, wherein when the pumping element drives the particles focused into each of the at least two localized stream lines in the at least one channel through the curved channel, the particles are focused into a single localized stream line formed in the curved channel.

15. The system of claim 14 , wherein the curved channel is symmetric and sigmoidal.

16. The system of claim 14 , wherein the curved channel is asymmetric and sigmoidal.

17. The system of claim 1 , further comprising a detector for detecting and enumerating particles focused in a localized stream line.

18. The system of claim 17 , further comprising a tagging system for tagging selected particles with a tag that can be detected by the detector, the detector thereby detecting and enumerating the selected particles.

19. The system of claim 18 , wherein the tag comprises magnetic beads coupled to one or more antibodies.

20. The system of claim 14 , further comprising a detector configured to detect the particles focused into the single localized stream line.