Method and system for accurate alignment and registration of array for DNA sequencing
In a genome sequencing system and methodology, a protocol is provided to achieve precise alignment and accurate registration of an image of a planar array of nanoballs subject to optical analysis. Precise alignment correcting for fractional offsets is achieved by correcting for errors in subperiod x-y offset, scale and rotation by use of minimization techniques and Moiré averaging. In Moiré averaging, magnification is intentionally set so that the pixel period of the imaging element is a noninteger multiple of the site period. Accurate registration is achieved by providing for pre-defined pseudo-random sets of sites, herein deletion or reserved sites, where nanoballs are prevented from attachment to the substrate so that the sites of the array can be used in a pattern matching scheme as registration markers for absolute location identification. Information can be extracted with a high degree of confidence that it is correlated to a known location, while at the same time the amount of information that can be packed on a chip is maximized.
1. A method comprising
preparing a planar two-dimensional substrate for imaging to establish location and registration of biochemical sites on the substrate by providing a predetermined two-dimensional pattern of biochemical sites on the substrate;
detecting image field spots in a spatial two-dimensional array on the substrate corresponding to biochemical sites in an image on the substrate;
aligning a spatial two-dimensional grid with image field spots of biochemical sites on the substrate to determine a grid offset; and
registering said grid points to known positions in a spatial two-dimensional field, the registering step including cross correlating the image field spots with a first known spatial two-dimensional image deletion pattern of image field spots on the substrate to determine absolute location within a field.
2. The method according to claim 1 , the deletion pattern in the periodic spatial pattern being selected to be pseudo random.
3. The method of claim 1 , the registering step comprising further cross correlating the image field spots with a second known image deletion pattern identifying location of the image field spots on the substrate.
4. The method of claim 1 , the preparing step comprising subtracting a background light level from the image.
5. The method of claim 4 , the subtracting step including:
finding intensity of the dimmest pixel within a defined array of pixels; and subtracting that intensity from each pixel the defined array.
6. The method of claim 1 , the image field spots detecting step including choosing the location of a brightest pixel associated with each field spot.
7. The method of claim 1 , the aligning step comprising a coarse fitting and a fine fitting.
8. The method of claim 1 , the aligning step comprising iteratively testing different combinations of rotation, scale, x-offset, and y-offset to find a tested combination having minimum least squares distances between each grid point and each field spot in the pattern of field spots.
9. The method of claim 1 , the aligning step further comprising:
forming the sum of the squared distances between each image field spot and its corresponding grid point; and
finding the minimum of the sum by:
calculating its partial derivatives with respect to rotation, scale, x-offset, and y-offset variables,
setting the partial derivatives equal to zero, and
solving the resulting system of linear equations.
10. The method of claim 1 , the alignment step including:
collecting image field spots by intensity group;
plotting group average spot brightness versus group average distance from nearest grid points; and
repeating the fine fitting step on all image field spots in groups for which the group average distance from the nearest grid point is less than a threshold value.
11. A device comprising:
a solid, planar substrate having discrete optically resolvable surface sites arranged according to a predetermined array pattern, said surface sites being modified to support biochemical experiments;
wherein said surface sites are located at image field spots in a predetermined spatial two-dimensional periodic array of spots on a surface of the substrate; and
wherein a fraction of the image field spots that would otherwise exist stand deleted from the array according to at least one known spatial two-dimensional deletion pattern.
12. The device of claim 11 , the deletion pattern in the two-dimensional periodic array being pseudo random.
13. The device of claim 11 , the fraction being between approximately 1% and approximately 3%.
14. The device of claim 11 , the array having at least one million spots.
15. The device of claim 11 , wherein only said surface sites of the substrate support biochemical experiments.
16. The device of claim 11 , areas of the substrate other than said surface sites being chemically treated to reduce non-specific binding of biomolecules.
17. The device of claim 11 , the biochemical experiments comprising combinatorial probe-anchor ligation with DNA nanoballs.
18. A method comprising:
providing a solid, planar substrate having discrete surface sites, the surface sites being modified to support biochemical experiments, the sites being located at spots in a predetermined spatial two-dimensional periodic array of spots on a surface of the substrate, and a fraction of the spots that would otherwise exist being deleted from the array according to a known deletion pattern;
performing biochemical experiments at the sites;
obtaining images of the biochemical experiments at the sites;
cross-correlating the image with the deletion pattern to determine absolute location of the spots; and
observing the images with subpixel accuracy to extract information about the biochemical experiments.
19. The method of claim 18 , the image observing step comprising weighting contributions of output from adjacent pixels based on exact location of the spots.
20. The method of claim 18 , the deletion pattern being pseudo random.
21. The method of claim 18 wherein the fraction is between approximately 1% and approximately 3%.
22. The method of claim 18 , wherein only said surface sites of the substrate support biochemical experiments.
23. The method of claim 18 , areas of the substrate other than said surface sites being chemically treated to reduce non-specific binding of biomolecules.
24. The method of claim 18 , the biochemical experiments comprising combinatorial probe-anchor ligation with DNA nanoballs.
25. The method according to claim 1 , wherein the imaging steps are configured to interact with a plurality of different fluorescent labels on molecules at each one of the biochemical sites, the preparing step including:
obtaining at least one fluorescence-specific image of the substrate for further processing of image data.
26. The method of claim 1 , the cross-correlating comprising interacting with a pattern having less than three percent of deleted grid points.
27. A system comprising:
a preprocessor for preparing a planar substrate for imaging to establish location and registration of biochemical sites on the substrate according to a predetermined spatial two-dimensional pattern;
a detector for detecting image field spots in the spatial two-dimensional pattern corresponding to biochemical sites in an image on the substrate;
a first subsystem for aligning a spatial two-dimensional grid with said image field spots; and
a second subsystem for registering grid points with said image field spots; the registering subsystem including a first cross correlator for cross correlating the image field spots with a first known deletion pattern of image field spots on the substrate to determine absolute location within a two-dimensional field.
28. The system of claim 27 , the second subsystem including a second cross correlator for cross correlating the image field spots with a second known deletion pattern identifying absolute location of the field spots on the substrate.
29. The system of claim 28 , at least the first known deletion pattern being pseudo random.