Ligand binding assays on microarrays in closed multiwell plates
Multiwell plates commonly used for immunoassay are increased in capacity and adapted for ease and speed of testing by forming a plurality of solid posts in each well of a plate. The posts and plate material and the dimensions of the posts are chosen to allow the immobilization of ligand patterns on an exterior wall of a post in a well and to permit a collimated beam of light directed to the post in a direction to achieve total internal reflection from a wall to generate an evanescent field in the plane of the ligands immobilized on the exterior wall of the post. The reflected light carries an image of localized intensity variations due to binding events between the ligand patterns and analytes in a sample introduced into a well. A cover plate seals the wells and provides for through holes for introducing sample material to the wells.
1. An apparatus for forming ligand binding assays for a plurality of analytes in a sample, comprising:
a first planar transparent plate including a first well therein; and
a first transparent solid post within the first well, said post having a height substantially equal to the height of said well and having at least one planar wall,
wherein said post has a thickness
t
≥
h
n
2
2
-
n
3
2
n
3
where t is the post thickness along the direction of a light beam propagation, h is the height of the post, n 2 is the index of refraction of the plate, and n 3 is the index of refraction of a sample introduced to the well.
2. The apparatus as in claim 1 , wherein said post has at least one planar side wall having an array of ligands immobilized thereon.
3. The apparatus as in claim 2 , wherein said post is of a material and has cross-sectional dimensions and a height to permit a beam of light directed at the post to produce total internal reflection at said at least one planar side wall and to generate an evanescent field in the plane of the array of ligands immobilized thereon.
4. The apparatus as in claim 3 , further comprising a second transparent plate juxtaposed with said first plate in a manner to seal said well, said second plate including a pair of through holes which is aligned with said well.
5. The apparatus as in claim 3 , wherein said post has a rectangular cross section with four planar walls.
6. The apparatus as in claim 5 , further comprising a source of a collimated beam of polarized light and means for directing said beam into the bottom of said post.
7. The apparatus as in claim 6 , further comprising means for capturing the image of the light intensity pattern reflected from the plane in said evanescent field.
8. The apparatus as in claim 2 , wherein said side wall includes a metallic film thereon and said plurality of ligands is formed on said film.
9. The apparatus as in claim 1 , wherein said plate includes a plurality of wells and each of said wells includes a plurality of posts, each post therein having at least one planar wall having an array of ligands immobilized thereon.
10. The apparatus as in claim 9 , wherein each of said posts is of a material and has cross sectional dimensions and a height to permit a beam of light directed to said posts to produce total internal reflection at the at least one planar wall of each post and to generate an evanescent field in the plane of the array of ligands immobilized on the at least one planar wall of each post.
11. The apparatus as in claim 10 , further comprising a second transparent plate juxtaposed with said first plate in a manner to seal said wells, said second plate including a plurality of through holes, each of said plurality of through holes being aligned with at least one of said wells sample to a well.
12. The apparatus as in claim 10 , further comprising a source of a beam of polarized light and means for directing said beam at different walls of said posts.
13. The apparatus as in claim 12 , further comprising means for capturing the image of the light intensity image reflected from a wall.
14. An imaging apparatus, comprising:
a first planar transparent plate including a first well; and
a first transparent post within the first well, said post having at least one planar wall,
wherein said post has a thickness
t
≥
h
n
2
2
-
n
3
2
n
3
where t is the post thickness along the direction of a light beam propagation, h is the height of the post, n 2 is the index of refraction of the plate, and n 3 is the index of refraction of a sample introduced to the well.
15. The apparatus as in claim 14 , wherein said post has at least one planar side wall having an array of ligands immobilized thereon.
16. The apparatus as in claim 15 , wherein said post is of a material and has cross-sectional dimensions and a height to permit a beam of light directed at the post to produce total internal reflection at said at least one planar side wall and to generate an evanescent field in the plane of the array of ligands immobilized thereon.
17. The apparatus as in claim 14 , further comprising a second transparent plate juxtaposed with said first plate in a manner to seal said well, said second plate including a pair of through holes which is aligned with said well.
18. The apparatus as in claim 14 , further comprising means for capturing an image of the light intensity pattern reflected from the plane in said evanescent field.
19. The apparatus as in claim 14 , further comprising means for capturing an image of spatially distributed polarization changes in a light beam reflected from the plane in said evanescent field.
20. The apparatus as in claim 14 , wherein said plate includes a plurality of wells and each of said wells includes a plurality of posts, each post therein having at least one planar wall having an array of ligands immobilized thereon.