Saturation binding ratiometric assay
Methods, devices, and reagents are described for performing ratiometric assays for hemoglobin A1c. The methods involve a direct ratio determination between Hb A1c and normalized total hemoglobin utilizing a saturating amount of hemoglobin so that Hb A1c binds proportionately to a substrate. In some applications, the assay utilizes a proximity label system for signal generation and/or labeled magnetic beads. The methods can be configured as homogeneous or heterogeneous assays.
1. An assay cartridge for determining an amount of glycated hemoglobin (HbA1c) in a blood sample, the assay cartridge comprising:
a) a channel, and (i) one or more zones, (ii) one or more chambers, or (iii) both;
b) an anti-hemoglobin (anti-Hb) first binding agent specific for binding to hemoglobin A (HbA), including un-glycated hemoglobin A (HbA0) and HbA1c, the first binding agent bound to a magnetic particle or a fluorescently labelled particle, the first binding agent disposed in the (i) channel, (ii) at least one of the one or more zones, or (iii) at least one of the one or more chambers;
c) an anti-HbA1c second binding agent that is (i) specific for binding to HbA1c that is bound to the first binding agent, (ii) bound to the other of the magnetic particle or fluorescently labelled particle, and (iii) disposed in the channel, the at least one of the one or more zones, or the at least one of the one or more chambers;
wherein the first binding agent comprises an antibody that binds within amino acid residues 3-30 or 7-25 of the beta subunit of HbA0 and HbA1c; and
wherein binding of hemoglobin to the first binding agent causes an amino terminal end of a hemoglobin beta chain of the hemoglobin to become exposed.
2. The assay cartridge of claim 1 , wherein the amount of HbA1c corresponds to a relative fraction of the HbA1c compared to (i) a total population of hemoglobin A (HbA) in the blood sample, or (ii) a total population of hemoglobin A (HbA) in the blood sample excluding the HbA1c.
3. The assay cartridge of claim 1 , wherein first binding agent binds within amino acid residues 3-8, 7-11, 7-12, 7-13, 8-12, 8-13, 9-13, 14-18, 19-23, 24-28, 3-12, 7-14, 7-15, 7-16, 7-18, 8-14, 8-15, 8-18, 9-15, 9-18, 14-23, 19-28, 21-30, 3-16, 7-20, 8-20, 9-22, 14-27, 17-30, 3-18, 7-22, 8-23, 9-24, 13-28, 3-20, 7-24, 8-25, 9-26, 13-30, 3-22, 7-25, 7-26, 8-27, 9-28, 11-30 3-27, or 7-30 of HbA.
4. The assay cartridge of claim 1 , wherein the first binding agent is bound to the magnetic particle and the second binding agent is bound to the fluorescently labelled particle.
5. The assay cartridge of claim 4 , wherein the first binding agent is bound to a plurality of labelled magnetic particles, wherein a number of the plurality of labelled magnetic particles correspond to a total hemoglobin bound to the first binding agent at saturation.
6. The assay cartridge of claim 5 , wherein the number of labelled magnetic particles is configured to be directly measured to minimize variability due to magnetic particle dispensing, magnetic particle movement, or both.
7. The assay cartridge of claim 1 , wherein the fluorescently labelled particle is a latex particle.
8. The assay cartridge of claim 1 , wherein the magnetic particle is labelled with a label which can be read separately from the fluorescently labelled particle.
9. The assay cartridge of claim 1 , wherein a hemoglobin binding capacity of the magnetic particle is pre-determined.
10. The assay cartridge of claim 1 , further comprising a lysis reagent configured to lyse red blood cells, the lysis reagent disposed in the (i) channel, (ii) at least one of the one or more zones, (iii) at least one of the one or more chambers, or (iv) any combination thereof.
11. The assay cartridge of claim 10 , wherein the lysis reagent, the first binding agent, the second binding agent, or any combination thereof, are in dry form.
12. The assay cartridge of claim 11 , wherein the lysis reagent is in dry form as fast reconstituting reagent pellets, such that the lysis reagent reconstitutes upon contact with a sample solution.
13. The assay cartridge of claim 1 , further comprising one or more additional binding agents for quantifying, detecting a presence, or both, of one or more hemoglobin isoforms S, C, E, D, F, or any combination thereof.