Systems and methods for particle focusing in microchannels
Various systems, methods, and devices are provided for focusing particles suspended within a moving fluid into one or more localized stream lines. The system can include a substrate and at least one channel provided on the substrate having an inlet and an outlet. The system can further include a fluid moving along the channel in a laminar flow having suspended particles and a pumping element driving the laminar flow of the fluid. The fluid, the channel, and the pumping element can be configured to cause inertial forces to act on the particles and to focus the particles into one or more stream lines.
1. A method for focusing particles suspended within a moving fluid, the method comprising:
providing a substrate including 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 );
flowing a fluid having a substantially constant kinematic viscosity (v) that includes suspended particles, each having a particle diameter (a), through the at least one channel; and
driving the fluid that includes the suspended particles through the at least one channel 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 α 2 /vD n ,
and resulting in forming one or more localized stream lines 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 method of claim 1 , wherein the aspect ratio is defined by a width and a height of the at least one channel, and wherein when the aspect ratio is substantially 1 to 1, the particles suspended in the fluid are focused into four localized stream lines.
3. The method of claim 1 , wherein the aspect ratio is defined by a width and a height of the at least one channel, and wherein when the aspect ratio is substantially 2 to 1, the particles suspended in the fluid are focused into two localized stream lines.
4. The method of claim 1 , wherein the at least one channel is a straight channel dimensioned and configured such that the particles suspended in the fluid are focused into each of at least two localized stream lines formed in the straight channel.
5. The method of claim 1 , wherein the at least one channel is a curved channel dimensioned and configured such that the particles suspended in the fluid are focused into a single localized stream line formed in the curved channel.
6. The method of claim 5 , wherein the curved channel is symmetric and sigmoidal.
7. The method of claim 5 , wherein the curved channel is asymmetric and sigmoidal.
8. The method of claim 5 , wherein a radius of curvature of the curved channel varies.
9. The method 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 and less than or equal to about 0.5.
10. The method of claim 1 , wherein the width defined by each localized stream line is about five times the particle diameter.
11. The method of claim 1 , further comprising:
flowing the fluid through at least first and second outlet branches at an outlet portion of the at least one channel; wherein at least one of the first and second outlet branches is located to receive the particles that are focused into a localized stream line.
12. The method of claim 1 , wherein the particles have a particle diameter in a range of 0.01 μm to 40 μm.
13. The method of claim 1 , further comprising driving the fluid that includes the suspended particles through the at least one channel such that the focused particles are spaced approximately evenly longitudinally within a localized stream line.
14. The method of claim 1 , wherein the aspect ratio is defined by a width and a height of the at least one channel, and wherein the aspect ratio varies along the at least one channel from about 1 at the inlet to about 2 at the outlet.
15. The method of claim 1 , further comprising detecting particles focused in a localized stream line.
16. The method of claim 1 , further comprising tagging selected particles with one or more tags.
17. The method of claim 16 , wherein the tag comprises a magnetic bead coupled to one or more antibodies that specifically bind to the selected particles.