Discontinuous fluidic systems for point-of-care analyte measurement
Disclosed herein are systems and methods for using the controlled movement of magnetic particles using controlled magnetic fields in a fluidic device containing separated fluidic regions to detect analytes in solution by immunoassay, such as an enzyme-linked immunosorbant assay (ELISA) for various medical and scientific applications. In order to achieve sequential exposure to the different chemical environments required in an immunoassay, magnetic particles are driven through fluid-containing chambers separated by air-gaps that may take the form of air bubbles or small open-air separations, for example. Externally controlled magnets coupled to actuators draw the flow of magnetic particles through air-liquid interfaces produced by microfluidic surface tension at the air-gap, washing the particles.
1. A method of detecting an analyte in a control or sample solution in a fluidic device, said device including a plurality of chambers separated by channels having an air-gap, comprising the steps of:
contacting a sample solution in a first chamber of said device with magnetic particles, wherein said magnetic particles comprise a primary binding agent that binds to an analyte in the sample solution; and wherein the first chamber comprises two opposed parallel walls;
moving the magnetic particles under the influence of a magnetic field from the first chamber and into a first channel having an air-gap therein, wherein the first channel comprises a lower wall which is aligned substantially transverse to the opposed parallel walls of the first chamber, and wherein an upper portion of one wall of the first chamber adjacent to the first channel transitions as a curve bending towards the lower wall of the first channel;
moving the magnetic particles under the influence of the magnetic field across the air-gap in the first channel and into a second chamber comprising two opposed parallel walls, wherein an upper portion of one wall of the second chamber is adjacent to the first channel and is also substantially parallel where it meets the lower wall of the first channel, and wherein the second chamber contains a second solution comprising a detection binding agent which is capable of binding to the analyte or to the primary binding agent;
removing unbound sample solution by passing the magnetic particles across the air-gap in the first channel;
moving the magnetic particles under the influence of the magnetic field through a second channel and across the air-gap therein and into a third chamber, wherein the third chamber contains an indicator capable of generating a signal indicating the presence of the detection binding agent;
removing unbound sample solution and second solution by passing the magnetic particles across the air-gap in the second channel; and
detecting the signal, wherein the presence of signal indicates analyte in the sample solution and the intensity of signal correlates with the quantity of analyte in the sample solution;
but wherein the magnetic particles are not moved to a wash chamber which contains solution capable of removing unbound reactants, as there is no such wash chamber in the fluidic device.
2. The method of claim 1 wherein the binding agents are one or more of: proteins, antibodies, peptides, aptamers, chemical moieties or nucleic acids.
3. The method of claim 1 wherein the primary binding agent is an antibody, and the analyte is an antibody or an antigen.
4. The method of claim 1 wherein the primary binding agent is an antigen, and the detection binding agent binds to an antibody which binds to the antigen.
5. The method of claim 1 wherein the plurality of chambers and the channels are contained in a cartridge.
6. The method of claim 5 wherein the cartridge is marked with an identifier that is capable of being read by a sensor or sensor camera for robotic or computational automation.
7. The method of claim 6 , wherein the identifier is a quick response code (QR-code) or bar code.
8. The method of claim 1 wherein the magnetic field is generated by permanent magnets which are moved in a linear path under external control.
9. The method of claim 8 where the movement of the permanent magnets is programmed.
10. The method of claim 9 further including moving the magnetic field in a second direction.
11. The method of claim 10 wherein the second direction is transverse to the linear path.
12. The method of claim 1 wherein movement of the magnetic field is varied in order to enhance movement of the magnetic particles in a desired direction.
13. The method of claim 1 wherein a light source and a detector are used to record the signal.
14. The method of claim 1 wherein the signal intensity is determined by examining and comparing the signal from pixels within an image.
15. The method of claim 1 wherein the signal is in the form of color, fluorescence, luminescence, or radioactivity.
16. The method of claim 15 wherein a color change is mediated by one or more of the following: PNPP (p-Nitrophenyl Phosphate), ABTS (2,2′-Azinobis [3-ethylbenzothiazoline-6-sulfonic acid]diammonium salt), OPD (o-phenylenediamine dihydrochloride), and TMB (3,3′,5,5′tetramethylbenzidine).
17. The method of claim 16 wherein TMB is reacted with horseradish peroxidase to generate the color change.