Systems and methods for particle focusing in microchannels

1. A system for focusing particles having a diameter (a) suspended within a moving fluid having a kinematic viscosity (v) into one or more localized stream lines, the system comprising:

a substrate;

at least one focusing channel provided on the substrate, wherein the at least one focusing channel comprises an inlet and an outlet and has a hydraulic diameter (D h ) configured such that a ratio of the particle diameter a to the hydraulic diameter D h is greater than or equal to about 0.07 and less than or equal to about 0.5;

and

a pumping element controlled to flow the moving fluid through the at least one focusing channel in a laminar flow at a maximum channel velocity (U m ) sufficient to maintain a channel Reynolds number (R c ) of the fluid flow greater than or equal to about 1 and less than or equal to about 250, wherein

R

c

=

U

m

⁢

D

h

v

;

such that inertial forces act on the particles and focus the particles having diameter a into one or more localized stream lines within the moving fluid in the at least one focusing channel.

2. The system of claim 1 , wherein the at least one focusing channel is a straight channel having a rectangular cross-sectional aspect ratio of about 1 to 1 and the pump is controlled to focus the particles having diameter a into four localized stream lines.

3. The system of claim 1 , wherein the at least one focusing channel is a straight channel having a rectangular cross-sectional aspect ratio of greater than 1 to 1 or a symmetrically curved channel having a rectangular cross-section and the pump is controlled to focus the particles having diameter a into two localized stream lines.

4. The system of claim 1 , wherein the at least one focusing channel is an asymmetrically curved channel having a rectangular cross-section and the pump is controlled to focus the particles having diameter a into a single localized stream line.

5. The system of claim 1 , wherein the at least one focusing channel is dimensioned such that the one or more focused stream lines have a width that is less than or equal to about five times the diameter a of the focused particles.

6. The system of claim 1 , wherein the at least one focusing channel is dimensioned such that the one or more focused stream lines have a width that is less than or equal to about three times the diameter a of the focused particles.

7. The system of claim 1 , wherein the at least one focusing channel is dimensioned such that the one or more focused stream lines have a width that is less than or equal to about two times the diameter a of the focused particles.

8. The system of claim 1 , further comprising at least first and second outlet channels on the substrate in fluid communication with the outlet of the at least one focusing channel, wherein at least one of the first and second outlet channels is located on the substrate so as to receive the particles having diameter a from the one or more focused stream lines.

9. The system of claim 8 , wherein the focusing increases the concentration of particles having diameter a in the one or more localized stream lines.

10. The system of claim 4 , further comprising at least first and second outlet channels on the substrate in fluid communication with the outlet of the at least one focusing channel, wherein at least one of the first and second outlet channels is located on the substrate so as to receive the particles having diameter a from the single localized stream line.

11. The system of claim 10 , wherein the focusing increases the concentration of particles having diameter a in the single localized stream line.

12. The system of claim 1 , wherein the at least one focusing channel has a rectangular cross-section.

13. The system of claim 12 , wherein the at least one rectangular channel has a width of less than or equal to about 1000 micrometers.

14. The system of claim 12 , wherein the at least one rectangular channel has a width of less than or equal to about 100 micrometers.

15. The system of claim 1 , wherein the particles comprise droplets comprising a liquid that is immiscible in the moving fluid and the system is configured to focus droplets having diameter a into one or more localized stream lines within the at least one focusing channel.

16. The system of claim 15 , wherein the droplets comprise silicone oil.

17. The system of claim 15 , wherein the at least one focusing channel is dimensioned such that in a moving fluid comprising different sized droplets larger droplets having a diameter a are focused while smaller droplets remain unfocused.

18. The system of claim 15 , further comprising at least first and second outlet channels on the substrate in fluid communication with the outlet of the at least one focusing channel, wherein at least one of the first and second outlet channels is located on the substrate so as to receive the droplets having diameter a from the one or more focused stream lines.

19. The system of claim 18 , wherein the at least one focusing channel is dimensioned such that in a moving fluid comprising different sized droplets larger droplets having diameter a are focused while smaller droplets remain unfocused and the larger droplets are received in the first outlet channel and smaller droplets are received in the second outlet channel.

20. The system of claim 19 , comprising five outlet channels arranged to receive five different ranges of droplet sizes from the at least one focusing channel.

21. The system of claim 1 , wherein each focusing channel comprises two or more inlets.