Single-sheath microfluidic chip

A microfluidic chip (100) for flowing a sample fluid mixture comprising sperm cells therethrough as a fluid stream, and for uniformly orienting and positioning the sperm cells flowed therethrough for interrogation and selective action, the microfluidic chip comprising:

• a. a sample micro-channel (110);
• b. two sheath fluid micro-channels (140);
• c. a first focusing region that includes an intersection region (145) formed by the two sheath fluid micro-channels (140) intersecting the sample micro-channel (110), wherein sheath fluid is introduced into the intersection region (145) by the two sheath fluid micro-channels (140), wherein the first focusing region combines geometric compression with the sheath fluid introduction;
• d. a downstream micro-channel (120) fluidly connected to and downstream of the intersection region (145), the downstream micro-channel (120) having a first straight portion, a constricting portion (122) downstream of the first straight portion, and a second straight portion downstream of the constricting portion (122), wherein the constricting portion (122) narrows in width only, wherein the constricting portion (122) only geometrically compresses the sample fluid mixture, wherein the second straight portion is narrower in width than the first straight portion, wherein the micro-channel (120) is configured to provide laminar flow;
• e. a second flow focusing region (130) fluidly connected to the downstream micro-channel (120) and downstream of the constricting portion (122) and the second straight portion, the second flow focusing region (130) comprising a positively sloping bottom surface (132) that reduces a height of the flow focusing region and sidewalls (135) that taper to reduce a width of the second flow focusing region, thereby geometrically constricting the second flow focusing region (130);
• and
• f. the sample fluid mixture comprising the sperm cells;
• wherein the first straight portion, the constricting portion (122), the second straight portion, and the second flow focusing region (130) are downstream of the intersection region (145),
• wherein the sample micro-channel (110) is configured to flow the sample fluid mixture, wherein the two sheath fluid micro-channels (140) are each configured to flow the sheath fluid into the intersection region (145) to cause laminar flow and to compress the sample fluid mixture flowing from the sample micro-channel (110) at least horizontally from at least two sides such that the sample fluid mixture becomes surrounded by sheath fluid and compressed into a thin stream.

A method of focusing particles in a fluid flow, comprising:

• a) providing a microfluidic chip (100) comprising:
• i. a sample micro-channel (110);
• ii. two sheath fluid micro-channels (140);
• iii. a first focusing region that includes an intersection region (145) formed by the two sheath fluid micro-channels (140) intersecting the sample micro-channel (110), wherein the first focusing region combines geometric compression with sheath fluid introduction;
• iv. a downstream micro-channel (120) fluidly connected to and downstream of the intersection region (135), the downstream micro-channel (120) having a first straight portion, a constricting portion (122) downstream of the first straight portion, and a second straight portion downstream of the constricting portion (122), wherein the constricting portion (122) narrows in width only, wherein the constricting portion (122) only geometrically compresses the sample fluid mixture, wherein the second straight portion is narrower in width than the first straight portion, wherein the micro-channel (120) is configured to provide laminar flow;
• and
• v. a second flow focusing region (130) fluidly connected to the downstream micro-channel (120) and downstream of the constricting portion (122) and the second straight portion, the second flow focusing region (130) comprising a positively sloping bottom surface (132) that reduces a height of the flow focusing region and sidewalls (135) that taper to reduce a width of the second flow focusing region, thereby geometrically constricting the second flow focusing region (130),
• wherein the first straight portion, the constricting portion (122), the second straight portion, and the second flow focusing region (130) are downstream of the intersection region (145);
• b) flowing a fluid mixture comprising the particles into the sample micro-channel (110) and into the intersection region (145);
• c) flowing a sheath fluid through the two sheath fluid micro-channels (140) and into the intersection region (145) such that the sheath fluid causes laminar flow and compresses the fluid mixture at least horizontally from at least two sides, wherein the fluid mixture becomes surrounded by sheath fluid and compressed into a thin stream, wherein the particles are constricted into the thin stream surrounded by the sheath fluid;
• d) flowing the fluid mixture and sheath fluids into the downstream micro-channel (120), wherein the constricting portion (122) of the downstream micro-channel (120) horizontally compresses the thin stream of fluid mixture;
• and
• e) flowing the fluid mixture and sheath fluids into the second flow focusing region (130), wherein the positively sloping bottom surface (132) and tapering sidewalls (135) further constrict the fluid mixture stream and re-orient the particles within the stream, thereby focusing the particles.

A method of producing a fluid with gender-skewed sperm cells, said method comprising:

• a) providing a microfluidic chip (100) comprising:
• i. a sample micro-channel (110);
• ii. two sheath fluid micro-channels (140);
• iii. a first focusing region that includes an intersection region (145) formed by the two sheath fluid micro-channels (140) intersecting the sample micro-channel (110), wherein the first focusing region combines geometric compression with sheath fluid introduction;
• iv. a downstream micro-channel (120) fluidly connected to and downstream of the intersection region (135), the downstream micro-channel (120) having a first straight portion, a constricting portion (122) downstream of the first straight portion, and a second straight portion downstream of the constricting portion (122), wherein the constricting portion (122) narrows in width only, wherein the constricting portion (122) only geometrically compresses the sample fluid mixture, wherein the second straight portion is narrower in width than the first straight portion, wherein the micro-channel (120) is configured to provide laminar flow;
• and
• v. a second flow focusing region (130) fluidly connected to the downstream micro-channel (120) and downstream of the constricting portion (122) and the second straight portion, the second flow focusing region (130) comprising a positively sloping bottom surface (132) that reduces a height of the flow focusing region and sidewalls (135) that taper to reduce a width of the second flow focusing region, thereby geometrically constricting the second flow focusing region (130),
• wherein the first straight portion, the constricting portion (122), the second straight portion, and the second flow focusing region (130) are downstream of the intersection region (145);
• b) flowing a semen fluid comprising sperm cells into the sample micro-channel (110) and into the intersection region (145);
• c) flowing a sheath fluid through the two sheath fluid micro-channels (140) and into the intersection region (145) such that the sheath fluid causes laminar flow and compresses the semen fluid at least horizontally from at least two sides, wherein the semen fluid becomes surrounded by sheath fluid and compressed into a thin stream;
• d) flowing the semen fluid and sheath fluids into the downstream micro-channel (120), wherein the constricting portion (122) of the downstream micro-channel (120) horizontally compresses the thin stream of semen fluid;
• e) flowing the semen fluid and sheath fluids into the second flow focusing region (130), wherein the positively sloping bottom surface (132) and tapering sidewalls (135) further constrict the semen fluid stream to focus the sperm cells at or near a center the semen fluid stream;
• f) determining a chromosome type of the sperm cells in the semen fluid stream, wherein each sperm cell is either a Y-chromosome-bearing sperm cell or an X-chromosome-bearing sperm cell;
• and
• g) sorting Y-chromosome-bearing sperm cells from X-chromosome-bearing sperm cells, thereby producing the fluid comprising gender-skewed sperm cells that are predominantly Y-chromosome-bearing sperm cells.