Microchip and microparticle fractionating device

1. A microchip comprising:

a main flow path through which a liquid containing microparticles flows; and

a branch flow path that branches from the main flow path;

wherein:

a cross-sectional area of a portion of the main flow path is substantially constant up to a branch start position or decreases toward the branch start position, and

a radius of curvature R of a side wall that connects a side wall of the main flow path and a side wall of the branch flow path is 0.5 mm or less and more than 0 mm, wherein the radius of curvature R is configured to decrease a vortex flow from occurring between the main flow path and the branch flow path.

2. The microchip according to claim 1 , wherein:

the microchip comprises an orifice section which is coaxial with the main flow path; and

the side wall that connects the side wall of the main flow path and the side wall of the branch flow path is between 0 μm and 300 μm from an orifice inlet to the orifice section.

3. The microchip according to claim 1 , wherein the cross-sectional area of the portion of the main flow path leading up to the branch start position is substantially constant, or decreases, so that the radius of curvature R of the side wall begins the branching of the branch flow path from the main flow path.

4. The microchip according to claim 1 , wherein a maximum cross-sectional area of the branch flow path is not more than half of the cross-sectional area of the main flow path at the branch start position.

5. The microchip according to claim 1 , wherein the branch flow path branches from the main flow path in a Y shape.

6. The microchip according to claim 1 , wherein a cross-sectional area of the branch flow path continuously decreases in an advancing direction of a flow of a liquid from a start position of the branch flow path.

7. The microchip according to claim 1 , wherein a cross-sectional area of the branch flow path continuously decreases from a start position of the branch flow path to a predetermined position in an advancing direction of a flow of a liquid and continuously increases from the predetermined position in the advancing direction of the flow of the liquid.

8. The microchip according to claim 1 , wherein a side wall of the branch flow path connected to an orifice section is bent toward an axis of the main flow path.

9. The microchip according to claim 1 , wherein:

the microchip comprises an orifice section which is coaxial with the main flow path; and

an angle of a side wall of the branch flow path connected to the orifice section with respect to an axis of the main flow path is 115 to 160 degrees.

10. The microchip according to claim 1 , wherein:

the microchip comprises an orifice section which is coaxial with the main flow path; and

an angle of a side wall of the branch flow path connected to the orifice section with respect to an axis of the main flow path is 125 to 160 degrees.

11. The microchip according to claim 1 , wherein:

the microchip comprises an orifice section which is coaxial with the main flow path; and

a pressure chamber communicates with the orifice section and a pressure in the pressure chamber is reduced or increased.

12. The microchip according to claim 11 , wherein microparticles are guided into the orifice section by reducing a pressure in the pressure chamber or microparticles are advanced to the branch flow path by increasing a pressure in the pressure chamber.

13. The microchip according to claim 1 , wherein:

the microchip comprises an orifice section which is coaxial with the main flow path; and

a flow path configured to form a flow of a liquid leading from the orifice section to the main flow path is provided in the orifice section, such that microparticles are advanced to the branch flow path due to the formed flow.

14. The microchip according to claim 1 , wherein:

the cross-sectional area of the portion of the main flow path leading up to the branch start position is constant up to the branch start position; and

the cross-sectional area of a second portion of the main flow path increases as it extends from the branch start position along the side wall.

15. A microparticle sorting device able to receive a microchip, the microchip comprising:

a main flow path through which a liquid containing microparticles flows; and

a branch flow path that branches from the main flow path;

wherein:

a cross-sectional area of a portion of the main flow path is substantially constant up to a branch start position or decreases toward the branch start position, and

a radius of curvature R of a side wall that connects a side wall of the main flow path and a side wall of the branch flow path is 0.5 mm or less, wherein the radius of curvature R is configured to decrease a vortex flow from occurring between the main flow path and the branch flow path.

16. The microparticle sorting device according to claim 15 , comprising:

a light source configured to irradiate microparticles flowing through the main flow path with light;

a detector configured to detect scattered light and/or fluorescence emitted from the microparticles; and

a processor configured to control an advancing direction of the microparticles flowing through the main flow path on a basis of data detected by the detector.

17. The microparticle sorting device according to claim 16 , wherein the processor controls a pressure in a pressure chamber communicating with an orifice section.

18. The microparticle sorting device according to claim 16 , wherein the processor controls a flow of a liquid in a flow path provided to form a flow of a liquid leading from an orifice section to the main flow path.