Paper substrate diagnostic apparatus and related methods and systems

1. An apparatus comprising:

a hydrophobic substrate having a first end and a second end opposite the first end;

a detection zone on a first surface of the substrate, the detection zone defining an area to sense an analyte in a sample, the detection zone comprising:

a first electrode and a second electrode disposed on the first surface of the substrate; and

a layer of hydrophilic ink disposed on the first and second electrodes and an area between the first and second electrodes; and

a channel comprising hydrophilic ink disposed on the first surface of the substrate, the channel having an inlet section adjacent the first end of the substrate, a middle section, and an outlet section in contact with the layer of hydrophilic ink, the channel to transfer a fluid sample from the inlet section to the layer of hydrophilic ink.

2. The apparatus of claim 1 further comprising a reagent layer disposed on a top surface of the first electrode, between the first electrode and the layer of hydrophilic ink.

3. The apparatus of claim 1 , wherein the first electrode is functionalized with a reagent.

4. The method of claim 1 , wherein the hydrophilic ink comprises micro-beads or nano-beads and a binder to adhere the micro-beads or nano-beads to the first surface of the substrate.

5. The apparatus of claim 4 , wherein the binder comprises at least one of polyvinyl chloride (PVC), polyvinylpyrrolidone (PVP), or nanofiber cellulose (NFC).

6. The apparatus of claim 1 further comprising:

a first contact disposed on the first surface of the substrate, the first contact electrically coupled to the first electrode;

a second contact disposed on the first surface of the substrate, the second contact electrically coupled to the second electrode; and

a reader comprising:

a slot to receive at least a portion of the substrate including the first contact and the second contact;

electrical connectors to receive signals from the first contact and the second contact; and

a processor to determine one or more of amperometric, voltammetric, or potentiometric measurements to sense a biomolecular interaction occurring in the detection zone via the first and second electrodes.

7. The apparatus of claim 6 , wherein the detection zone further comprises a third electrode and the processor is to sense the biomolecular interaction by comparing (1) a difference in the first and second electrodes and (2) a difference in the second and third electrodes.

8. The apparatus of claim 6 , wherein the detection zone comprises a plurality of additional electrodes, and the processor is to determine a plurality of measurements using the plurality of additional electrodes.

9. The apparatus of claim 1 , wherein the substrate comprises paper.

10. The apparatus of claim 1 , wherein the substrate is flexible and printable.

11. The apparatus of claim 1 , wherein the second electrode is disposed closer to the first end of the substrate than the first electrode, the second electrode being a ground electrode.

12. The apparatus of claim 1 further including a regent disposed between the first surface and the layer of hydrophilic ink.

13. The apparatus of claim 1 further including a reagent disposed between the first surface and the channel.

14. The apparatus of claim 1 , wherein the substrate includes a recess formed in the first surface, the channel disposed in the recess.

15. The apparatus of claim 14 , wherein the channel is substantially even with the first surface adjacent the recess.

16. The apparatus of claim 15 , wherein the first electrode, the second electrode and the layer of hydrophilic ink are disposed in the recess.