Detection of microscopic objects

1. A detection disc for carrying samples in an apparatus for detection of microscopic objects in a fluid, the detection disc including a detection channel and a separate focus structure, wherein the focus structure comprises a groove located outside of the detection channel, said groove comprising sloping sidewalls provided in a first surface of the detection disc, wherein an angle between each sidewall of the groove and the first surface is greater than a critical angle of the detection disc such that when the detection disc is illuminated with a light beam that enters the detection disc from a second surface that is opposite the first surface, light from the light beam is internally reflected by said sidewalls of said groove and light from the light beam is transmitted through a bottom of said groove to a greater extent as compared to said sidewalls to allow for contrast-based focusing between the bottom of the groove and the sidewalls of the groove.

2. A detection disc according to claim 1 , wherein the disc is made from a material with refractive index of greater than 1.22.

3. A detection disc according to claim 1 , wherein the disc is made from a cyclo olefin polymer.

4. A detection disc according to claim 1 wherein the focus structure has a V-shaped cross-section.

5. A detection disc according to claim 1 , wherein a depth of the focus structure is less than a depth of the channel.

6. A detection disc according to claim 1 , wherein a depth of the channel is twice a depth of the focus structure.

7. A substrate for use in manufacture of a production master plate for production of a detection disc for carrying samples in an apparatus for detection of microscopic objects in a fluid, the substrate including a channel and a separate focus structure for forming a corresponding channel and a corresponding separate focus structure in the detection disc for focusing an associated imaging apparatus at a predefined imaging plane in the detection disc, wherein the focus structure of the substrate comprises a groove located outside of the channel, said groove comprising sloping sidewalls provided in a first surface of the substrate, wherein an angle between each sidewall of the groove and the first surface of the substrate is greater than a critical angle of the detection disc, and wherein the corresponding focus structure of the detection disc comprises a corresponding groove with sloping sidewalls provided in a first surface of the detection disc with an angle between each sidewall of the corresponding groove and the first surface of the detection disc being greater than the critical angle of the detection disc, such that when the detection disc is illuminated with a light beam that enters the detection disc from a second surface of the detection disc that is opposite the first surface of the detection disc, the light beam is internally reflected by said sidewalls of said corresponding groove and the light beam is transmitted through a bottom of said corresponding groove to a greater extent as compared to said sidewalls of said corresponding groove to allow for contrast-based focusing between the bottom of the corresponding groove and the sidewalls of the corresponding groove.

8. An apparatus for detecting and/or counting microscopic objects comprising:

a detection disc for carrying samples for detection of microscopic objects in a fluid, the detection disc including a detection channel and a separate focus structure, wherein the focus structure comprises a groove located outside of the detection channel;

a first imaging apparatus for finding a focal plane by focusing on the focus structure;

a second imaging apparatus for counting the objects in the detection channel, the second imaging apparatus being focused to a second focal plane using information about the focal plane from the first imaging apparatus, wherein the second focal plane is the same as the focal plane found by the first imaging apparatus or is at an offset from the focal plane found by the first imaging apparatus;

wherein the focus structure groove comprises sloping sidewalls provided in a first surface of the detection disc, and wherein an angle between each sidewall of the focus structure and the first surface is greater than a critical angle of the detection disc such that when the detection disc is illuminated with a light beam that enters the detection disc from a second surface that is opposite the first surface, the light beam is internally reflected by said sidewalls of said groove and the light beam is transmitted through a bottom of said groove to a greater extent as compared to said sidewalls to allow for contrast-based focusing between the bottom of the groove and the sidewalls of the groove.