Controlled dispensing of samples onto substrates
Methods for dispensing a fluid sample on a substrate include obtaining an image of a sample applicator in proximity to the substrate, where the image includes a first image of the sample applicator and a second image of the sample applicator, determining a height of the sample applicator relative to a surface plane of the substrate based on a distance between common portions of the first and second images, and dispensing the fluid sample onto the substrate using the sample applicator, where the dispensing includes: translating the sample applicator, translating the substrate, or translating both the sample applicator and the substrate to effect a relative translation between the sample applicator and the substrate; and maintaining the sample applicator within 2 microns of a target height relative to the surface plane of the substrate during the translating.
1. A method for preparing a sample on a substrate, the method comprising:
obtaining an image of a sample applicator in proximity to the substrate, the image comprising a direct image region corresponding to the sample applicator and a first reflected image region corresponding to an image of the sample applicator reflected from a surface of the substrate;
determining edge positions of the sample applicator in the direct and first reflected image regions, and a distance between the positions;
determining a position of the sample applicator relative to a surface of the substrate based on the distance; and
dispensing the sample onto the substrate using the sample applicator while maintaining the sample applicator at a controlled height above the substrate surface,
wherein the sample applicator comprises a wall having a thickness measured in a direction orthogonal to a central axis of the sample applicator of between 30 microns and 300 microns, the wall defining an internal channel in the sample applicator; and
wherein the internal channel comprises:
a first channel portion having a first cross-sectional shape centered on the central axis; and
a second channel portion having a second cross-sectional shape that is not centered on the central axis.
2. The method of claim 1 , further comprising dispensing the sample onto the substrate at a rate of 0.020 μL/s or more.
3. The method of claim 1 , wherein the second channel portion terminates at a tip of the sample applicator.
4. The method of claim 3 , wherein the first channel portion has a first maximum cross-sectional dimension, and wherein the second channel portion has a second maximum cross-sectional dimension that is smaller than the first maximum cross-sectional dimension.
5. The method of claim 1 , wherein the first and second cross-sectional shapes are different.
6. The method of claim 1 , wherein the first cross-sectional shape is circular.
7. The method of claim 6 , wherein the second cross-sectional shape is non-circular.
8. The method of claim 7 , wherein the second cross-sectional shape is elliptical.
9. The method of claim 7 , wherein an internal wall of the second channel portion has a radial dimension that varies relative to a position on the central axis.
10. The method of claim 1 , wherein the wall thickness is between 50 microns and 150 microns.
11. The method of claim 4 , wherein the internal channel comprises a third channel portion having a maximum cross-sectional dimension that varies along an axial direction of the sample applicator from the first maximum cross-sectional dimension to the second maximum cross-sectional dimension.
12. The method of claim 11 , wherein the maximum cross-sectional dimension of the third channel portion decreases in a direction toward a tip of the sample applicator.
13. The method of claim 4 , wherein the internal channel comprises a third channel portion having a cross-sectional area that varies along an axial direction of the sample applicator.
14. The method of claim 13 , wherein the cross-sectional area of the third channel portion decreases in a direction toward a tip of the sample applicator.
15. The method of claim 11 , wherein an axis of the third channel portion is inclined relative to an axis of the first channel portion.
16. The method of claim 1 , wherein at least a portion of the second channel portion is beveled along its length.
17. The method of claim 4 , wherein the first maximum cross-sectional dimension is between 400 microns and 650 microns.
18. The method of claim 4 , wherein the second maximum cross-sectional dimension is between 200 microns and 400 microns.