Three-dimensional (3D) hydrodynamic focusing using a microfluidic device

1. An apparatus, the apparatus being a planar microfluidic device, the apparatus comprising:

a substrate;

a sample flow inlet, configured to receive a sample flow;

a first flow inlet, configured to receive a first sheath flow;

a curved channel, the curved channel configured to receive the sample flow adjacent to the first sheath flow,

the sample flow inlet, the first flow inlet, and the curved channel being supported by the substrate,

the curved channel having a bend angle,

the curved channel being configured to provide vertical hydrodynamic focusing of the sample flow when the sample flow and first sheath flow pass together through the curved channel,

the sample flow being compressed along a direction normal to the substrate to form a horizontal sample flow sandwiched between split vertical focusing sheath flows;

at least one inlet for an in-plane hydrodynamic focusing sheath flow; and

an output channel, receiving the sample flow, the first sheath flow, and the in-plane hydrodynamic focusing sheath flow,

the first sheath flow and the in-plane hydrodynamic focusing sheath flow together providing three-dimensional hydrodynamic focusing of the sample flow within the output channel,

the sample flow, the first sheath flow, and the in-plane hydrodynamic focusing sheath flows being co-planar.

2. The apparatus of claim 1 , further including a laser configured to excite the sample flow within the output channel.

3. The apparatus of claim 2 , further including a radiation detector configured to receive radiation from the sample flow, the radiation being induced by the laser.

4. The apparatus of claim 1 , the curved channel having a bend angle of between 135 degrees and 225 degrees, inclusive.

5. The apparatus of claim 1 , the curved channel having a bend angle of approximately 180 degrees.

6. The apparatus of claim 1 , said in-plane hydrodynamic focusing sheath flow horizontally crossing the direction of said sample flow.

7. The apparatus of claim 1 , said in-plane hydrodynamic focusing sheath flow intersecting said sample flow downstream from said curved channel.

8. An apparatus, the apparatus being a planar microfluidic device configured to receive a sample flow, a first sheath flow, and an in-plane hydrodynamic focusing sheath flow, the apparatus comprising:

a substrate;

a sample flow inlet configured to receive the sample flow;

a first sheath inlet configured to receive the first sheath flow;

the sample flow inlet being configured adjacent to the first sheath flow inlet;

a curved channel supported by and generally parallel to the substrate,

the sample flow inlet and first sheath inlet being configured to deliver the sample flow and the first sheath flow to the curved channel,

the curved channel being configured to provide hydrodynamic focusing of the sample flow, the sample flow being compressed in a direction normal to the substrate to form a horizontal sample flow sandwiched between split vertical focusing sheath flows;

at least one inlet configured to receive the in-plane focusing sheath flow;

an output channel, the first sheath flow and the in-plane hydrodynamic focusing sheath flow together providing three-dimensional hydrodynamic focusing of the sample flow within the output channel;

an excitation source configured to excite the sample flow at an excitation point within the output channel; and

a radiation detector configured to receive detected radiation from the excitation point.

9. The apparatus of claim 8 , the excitation source being a laser, laser radiation being conveyed to the output channel by an optical path including an optical fiber.

10. The apparatus of claim 8 , the detected radiation including fluorescence.

11. The apparatus of claim 8 , the detected radiation being scattered radiation.

12. The apparatus of claim 8 , further comprising a first optical fiber configured to convey radiation from excitation source to the excitation point, and a second optical fiber configured to collect radiation from the excitation point.

13. The apparatus of claim 8 , the apparatus being a single-layer planar microfluidic flow cytometer.

14. The apparatus of claim 8 , the curved channel having a bend angle at least 135 degrees.

15. The apparatus of claim 8 , the curved channel having a bend angle of at least 180 degrees.

16. The apparatus of claim 8 , the curved channel having a bend angle between 135 degrees and 225 degrees.

17. The apparatus of claim 8 , the sample flow having a focus width at the excitation point, the focus width being less than 10 microns.

18. A method of hydrofluidic focusing a sample flow in a planar microfluidic device having a planar substrate, the sample flow being a fluidic suspension of particles, the method comprising:

passing the sample flow and an adjacent sheath flow through a curved channel section disposed on the planar substrate to induce horizontal drifting of said sample flow to form a horizontal sample flow sandwiched between split vertical focusing sheath flows, the curved channel section providing hydrofluidic focusing of the sample flow in a direction generally normal to the planar substrate;

passing the sample flow through a linear channel section between a pair of in-plane focusing sheath flows so as to obtain three-dimensional hydrofluidic focusing of the sample flow within an output channel,

the sample flow, the sheath flow, and the pair of in-plane focusing sheath flows being generally coplanar; and

characterizing the particles within the output channel.

19. The method of claim 18 , the sample flow including biological cells,

the method including hydrodynamic focusing of the biological cells within the sample flow to allow characterization of the biological cells.

20. The method of claim 18 , the sample flow including fluorescent molecules,

the method including hydrodynamic focusing of the fluorescent molecules to facilitate detection of the fluorescent molecules using single-molecule fluorescence spectroscopy.