Robust colorimetric processing method for paper based sensors
The present disclosure proposes a colorimetric method that couples sensor design with image processing to enable automated evaluation of test results obtained by paper-based sensors. The proposed method can match ink color and dye used in colorimetric reaction in terms of their absorption in spectral range (e.g., red, green, blue). A near-zero absorption channel can then be used to normalize absorption channels and construct a composite image.
1. A colorimetric processing method for paper based sensors, comprising:
using a camera and taking a picture of a colorimetric paper sensor for colorimetric reactions;
identifying the type of paper sensor by image processing;
identifying one color channel in which both a dye and reference color have near zero absorption and wherein the color channels in which both the dye and the reference color have absorption;
identifying the known absorption ratio between the dye and the reference color in each color channel;
separating each test area in the channel from the non-test areas;
normalizing each absorption channel by the near zero absorption channel to remove spatial variation;
calibrating the test area reading with the reference color and a substrate white in the composite image; and,
reporting the concentration of a test substance analyte based on the calibrated reading in each test area.
2. The method according to claim 1 , further comprising:
locating the test areas in the near zero absorption channels by image processing.
3. The method according to claim 2 , further comprising:
using an additional camera and taking another picture of the colorimetric paper sensor to construct a composite image from one or more absorption channels.
4. The method according to claim 1 , wherein the colorimetric paper sensor is a biomedical paper sensor for determining a concentration of biological materials in fluids comprising:
a plurality of axial symmetric test zones;
wherein the test zones radiate outward from a central point;
each of the axial symmetric test zones divided by wax ink barrier walls;
each of the axial symmetric test zones contain a unique test reagent therein;
a reference region surrounding the plurality of axial test zones; and,
wherein the reference region includes a first calibration color area including a first predeterminable color for comparing to one or more of the axial test zones.
5. The method according to claim 4 , wherein the plurality of test zones is at least two.
6. The method according to claim 4 , wherein the biomedical paper sensor further comprises:
a total device area including the combined areas of a reference region area and the axial test zones area; and,
wherein the axial test zones area is at least 37.5% of the total device area.
7. The method according to claim 4 , wherein an area of each of the axial symmetric test zones is at least 5 mm 2 .
8. The method according to claim 4 , wherein the wax ink barrier walls include a thickness of at least 100 μm.
9. The method according to claim 6 , wherein the reference region area further includes a substrate region separating the axial test zones area and the calibration color area.
10. The method according to claim 4 , wherein the reference region further includes a second calibration color area including a second predeterminable color for comparing to one or more of the axial test zones; and,
wherein the first and second calibration color areas each include first and second predeterminable colors, respectively, for comparing to one or more of the axial test zones to report the concentration of at least two test substance analytes based on the calibrated reading in each test area.
11. A colorimetric processing method for paper based sensors, comprising:
taking a picture of a colorimetric paper sensor for colorimetric reactions;
identifying the type of paper sensor by image processing;
identifying one color channel in which both a dye and reference color have near zero absorption and wherein the color channels in which both the dye and the reference color have absorption;
identifying the known absorption ratio between the dye and the reference color in each color channel;
separating each test area in the channel from the non-test areas;
normalizing each absorption channel by the near zero absorption channel to remove spatial variation;
wherein the colorimetric paper sensor is a biomedical paper sensor;
wherein the paper sensor includes a plurality of axially radiating test zones;
each of the axially radiating test zones divided by wax ink barrier walls;
each of the axially radiating test zones contain a unique test reagent therein;
a reference region surrounding the plurality of axially radiating test zones; and,
wherein the reference region includes a calibration color area including a predeterminable color for comparing to one or more of the axially radiating test zones.
12. The method according to claim 11 , wherein the paper sensor includes:
a total device area including the combined areas of a reference region area and the axially radiating test zones area; and,
wherein the axially radiating test zones area is at least 37.5% of the total device area.
13. The method according to claim 12 , wherein the reference region area further includes a substrate region separating the axially radiating test zones area and the calibration color area.
14. A colorimetric processing method for paper based sensors, comprising:
taking a picture of a colorimetric paper sensor for colorimetric reactions;
identifying the type of paper sensor by image processing;
identifying one color channel in which both a dye and reference color have near zero absorption and wherein the color channels in which both the dye and the reference color have absorption;
identifying the known absorption ratio between the dye and the reference color in each color channel;
separating each test area in the channel from the non-test areas;
normalizing each absorption channel by the near zero absorption channel to remove spatial variation;
wherein the colorimetric paper sensor is a biomedical paper sensor;
wherein the paper sensor includes a plurality of axially radiating test zones;
each of the axially radiating test zones divided by wax ink barrier walls;
each of the axially radiating test zones contain a unique test reagent therein;
a reference region surrounding the plurality of axially radiating test zones;
a total device area including the combined areas of a reference region area and the axially radiating test zones area;
wherein the axially radiating test zones area is at least 37.5% of the total device area; and,
wherein the reference region area further includes a substrate region separating the axially radiating test zones area and the calibration color area.
15. The method of claim 14 , wherein the reference region includes a calibration color area including a predeterminable color for comparing to one or more of the axially radiating test zones.
16. A colorimetric processing method for paper based sensors, comprising:
taking a picture of a colorimetric paper sensor for colorimetric reactions;
identifying the type of paper sensor by image processing;
identifying one color channel in which both a dye and reference color have near zero absorption and wherein the color channels in which both the dye and the reference color have absorption;
identifying the known absorption ratio between the dye and the reference color in each color channel;
separating each test area in the channel from the non-test areas;
normalizing each absorption channel by the near zero absorption channel to remove spatial variation; and,
wherein the colorimetric paper sensor is a biomedical paper sensor.
17. The method according to claim 16 , wherein a number of test areas is at least two.
18. The method according to claim 16 , wherein the biomedical paper sensor further comprises:
a total device area including the combined areas of a reference region area and the axial test zones area; and,
wherein the axial test zones area is at least 37.5% of the total device area.
19. The method of claim 16 , wherein the paper sensor includes a structural forming layer having a reference region surrounding a plurality of axially radiating test zones; and,
wherein said reference region includes a calibration color area including a predeterminable color for comparing to one or more of the plurality of axially radiating test zones.
20. The method of claim 19 , wherein said reference region includes another calibration color area including a predeterminable color for comparing to one or more of the plurality of axially radiating test zones.
21. The method of claim 20 , further comprising:
using an additional camera and taking another picture of the colorimetric paper sensor to construct a composite image from one or more absorption channels.