Planar waveguide based cartridges and associated methods for detecting target analyte
A cartridge for processing a sample includes (a) a planar waveguide with upper and lower planar surfaces defining an optical axis therebetween, wherein the upper planar surface has a plurality of capture molecules bound thereto, (b) a lens portion, coupled to the planar waveguide, for focusing and refracting a light beam propagating parallel to, but offset from, the optical axis such that the light beam couples into the planar waveguide and propagates therein along the optical axis at a non-zero, internal propagation angle β relative to the upper planar surface, and (c) a sample chamber for positioning the sample in contact with the plurality of capture molecules such that a target analyte of the sample is detectable through (i) an assay involving the target analyte and the capture molecules and (ii) evanescent illumination of the assay using the light beam within the planar waveguide.
1. A cartridge for processing a sample, comprising:
a planar waveguide with upper and lower planar surfaces defining an optical axis therebetween, the optical axis being perpendicular to a normal vector of the upper and lower planar surfaces, the upper planar surface having a plurality of capture molecules bound thereto;
a cylindrical lens portion, coupled to the planar waveguide, for focusing and refracting a light beam propagating parallel to, but offset from, the optical axis such that the light beam couples into the planar waveguide and propagates therein along the optical axis at a non-zero, internal propagation angle β relative to the upper planar surface; and
a sample chamber for positioning the sample in contact with the plurality of capture molecules such that a target analyte of the sample is detectable through (a) an assay involving the target analyte and the capture molecules and (b) evanescent illumination of the assay using the light beam within the planar waveguide;
the cylindrical lens portion having:
(a) a thickness t between the upper planar surface and an apex of the cylindrical lens portion such that the light beam focuses at a distance L in direction parallel to the optical axis from a circle center defined by a curved surface of the cylindrical lens portion, the thickness t being measured along direction parallel to the normal vector,
(b) an index of refraction n, and
(v) a radius R that, for a diameter D of the light beam, cooperates with the thickness t, the horizontal distance L, and the index of refraction n to produce a range of the internal propagation angle β that provides uniform evanescent field strength within a detection region of the sample chamber; and
the cylindrical lens portion being configured to receive the light beam such that its center is offset from an apex of the cylindrical lens portion by a distance y, parallel to the normal vector, from an apex of the cylindrical lens portion to the center of the light beam, and the cylindrical lens portion being characterized by the equations
y
=
R
[
1
-
n
sin
β
1
-
2
n
cos
β
+
n
2
]
,
t
=
R
+
(
y
-
R
)
3
R
2
n
2
,
and
L
=
t
-
y
tan
β
-
2
yR
-
y
2
.
2. The cartridge of claim 1 , all angles within the range of the internal propagation angle β being shallower than critical angle for total internal reflection.
3. The cartridge of claim 1 , the detection region being a distance away from the cylindrical lens portion along the optical axis to ensure the uniform evanescent field strength.
4. The cartridge of claim 1 , the cylindrical lens portion being truncated such that it does not extend beyond the distance L in direction parallel to the optical axis.
5. The cartridge of claim 1 , the planar waveguide and the cylindrical lens portion being integrally formed within common optically transmissive material.
6. The cartridge of claim 5 , the cylindrical lens portion having a first planar surface that is coplanar with the upper planar surface, the first planar surface and the upper planar surface cooperating to form a floor of the sample chamber such that the cylindrical lens portion couples the light beam into the planar waveguide within region of the planar waveguide occupied by the sample chamber.
7. The cartridge of claim 1 , the planar waveguide being formed of an optically transparent material selected from the group consisting of cyclic olefin polymer, cyclic olefin copolymer, polyolefin, polystyrene, acrylic, polymethylmethacrylate, and polycarbonate.
8. The cartridge of claim 1 , the upper planar surface being modified using a process selected from the group consisting of plasma activation, chemical vapor deposition, liquid phase deposition, and surface polymerization of an activation chemistry, and combinations thereof.
9. A method for detecting a target analyte in a cartridge, comprising:
receiving, into a cylindrical lens portion, a light beam propagating parallel to, but offset from, an optical axis for light propagation within a planar waveguide between upper and lower planar surfaces of the planar waveguide, said offset being in direction parallel to normal vector of the lower planar surface, the cylindrical lens portion having an index of refraction n, a radius R, and a thickness t between the upper planar surface and an apex of the cylindrical lens portion along a direction parallel to the normal vector;
using the cylindrical lens portion, refracting and focusing the light beam to (a) couple the light beam into the planar waveguide such that the light beam is incident on the upper planar surface of the planar waveguide at a non-zero, internal propagation angle β relative to the upper planar surface, and (b) focus the light beam at a horizontal distance L from a circle center defined by a curved surface of the cylindrical lens portion; and
propagating the light beam within the planar waveguide at a range of the internal propagation angle β to evanescently illuminate, with uniform evanescent field strength within a detection region of the sample chamber, a plurality of capture molecules bound to the upper planar surface within a sample chamber such that a target analyte of a sample interacting with the plurality of capture molecules produces a light signal, the range of the internal propagation angle β being determined by the index of refraction n, the radius R, the thickness t, the diameter D, and the horizontal distance L;
wherein the step of receiving includes receiving the light beam such that a center of the light beam is offset by a distance y, parallel to the normal vector, from an apex of the cylindrical lens portion to the center of the light beam, the cylindrical lens portion being characterized by the equations
y
=
R
[
1
-
n
sin
β
1
-
2
n
cos
β
+
n
2
]
,
t
=
R
+
(
y
-
R
)
3
R
2
n
2
,
and
L
=
t
-
y
tan
β
-
2
yR
-
y
2
.
10. The method of claim 9 , in the step of receiving, all of the light beam being offset from the planar waveguide in direction away from the lower planar surface along the normal vector.
11. The method of claim 9 , in the step of evanescently illuminating, all angles within the range of the internal propagation angle β being shallower than critical angle for total internal reflection.
12. The method of claim 9 , the step of refracting and focusing comprising coupling the light beam into the planar waveguide within region of the planar waveguide occupied by the sample chamber.
13. The method of claim 9 , in the step of evanescently illuminating, the detection region being a distance away from the cylindrical lens portion along the optical axis to ensure the uniform evanescent field strength.
14. The method of claim 9 , in the step of evanescently illuminating, the plurality of capture molecules including at least one molecule selected from the group consisting of a peptide, a polypeptide, a protein, an antibody, an antigen, a polysaccharide, sugar, an oligonucleotide, a polynucleotide, a synthetic molecule, an inorganic molecule, an organic molecule, and combinations thereof.
15. The method of claim 9 , in the step of evanescently illuminating, the sample containing an antibody and an antigen, the method further comprising detecting both the antibody and the antigen through detection of respective light signals.
16. The method of claim 9 , the step of receiving comprising receiving the light beam as a homogenized laser beam such that evanescent field strength in the step of evanescently illuminating is free of speckle.