Devices and systems for optically determining a concentration of an analyte in a living subject using hydrogel-based, fluorescent microneedles and methods of manufacture thereof

1. An apparatus comprising:

a microneedle made of a dried hydrogel material that transmits light in a first wavelength range and transmits light in a second wavelength range, wherein the microneedle is sized and shaped to penetrate a stratum corneum of a live subject and access a dermal interstitial fluid layer of the subject, and wherein the dried hydrogel material is formed by drying a hydrated hydrogel material having a shrinkage percentage of less than 30%; and

a fluorescent substance disposed in the microneedle, wherein the substance fluoresces in the second wavelength range when illuminated by light in the first wavelength range when the substance interacts with an analyte, wherein a magnitude of the fluorescence varies as a function of a concentration of the analyte.

2. The apparatus of claim 1 , wherein the dried hydrogel material comprises poly(2-hydroxyethyl methacrylate).

3. The apparatus of claim 1 , wherein the dried hydrogel material comprises a dried polyacrylamide hydrogel.

4. The apparatus of claim 1 , wherein the dried hydrogel material comprises a polyacrylamide hydrogel having a high percentage of AAm and a low AAm/MBAm ratio.

5. The apparatus of claim 4 , wherein the polyacrylamide hydrogel has an AAm percentage between 28 and 32 and an AAm/MBAm ratio between 14 and 16.

6. The apparatus of claim 4 , wherein the polyacrylamide hydrogel has an AAm percentage between 29 and 31 and an AAm/MBAm ratio between 14.5 and 15.5.

7. An apparatus comprising:

a hydrogel base having an upper surface and a lower surface;

a plurality of microneedles affixed to the lower surface of the hydrogel base, wherein the plurality of microneedles are made of a dried hydrogel material that transmits light in a first wavelength range and transmits light in a second wavelength range, and wherein the plurality of microneedles are sized and shaped to penetrate a stratum corneum of a live subject and access a dermal interstitial fluid layer of the subject; and

a fluorescent substance disposed in the plurality of microneedles, wherein the substance fluoresces in the second wavelength range when illuminated by light in the first wavelength range when the substance interacts with an analyte, wherein a magnitude of the fluorescence varies as a function of a concentration of the analyte.

8. The apparatus of claim 7 , wherein the upper surface of the hydrogel base is concave.

9. The apparatus of claim 8 , wherein the concave shape of the upper surface of the hydrogel base is shaped to focus light in the second wavelength range onto a photosensor.

10. The apparatus of claim 7 , wherein the fluorescent substance is not incorporated into the hydrogel base.

11. The apparatus of claim 7 , wherein the plurality of microneedles have diameters between 175 and 225 μm and lengths between 1300 and 1500 μm.

12. The apparatus of claim 7 , wherein the dried hydrogel material comprises a polyacrylamide hydrogel having a high percentage of AAm and a low AAm/MBAm ratio.

13. The apparatus of claim 12 , wherein the polyacrylamide hydrogel has an AAm percentage between 28 and 32 and an AAm/MBAm ratio between 14 and 16.

14. The apparatus of claim 12 , wherein the polyacrylamide hydrogel has an AAm percentage between 29 and 31 and an AAm/MBAm ratio between 14.5 and 15.5.

15. A method of fabricating an array of hydrogel microneedles affixed to a base, the method comprising:

adding a fluorescent substance to a first quantity of hydrogel material, wherein the substance fluoresces in a second wavelength range when illuminated by light in a first wavelength range when the substance interacts with an analyte, wherein a magnitude of the fluorescence varies as a function of a concentration of the analyte;

introducing the first quantity of hydrogel material with the added fluorescent substance into a plurality of needle shaped wells located at a bottom of a mold;

introducing a second quantity of hydrogel material into an upper portion of the mold above the first quantity of hydrogel material disposed in the needle shaped wells, wherein the second quantity of hydrogel material forms a base for the first quantity of hydrogel material disposed in the needle shaped wells;

removing the first quantity of hydrogel material and the second quantity of hydrogel material from the mold; and

drying the first quantity of hydrogel material and the second quantity of hydrogel material,

wherein the dried first quantity of hydrogel material and the dried second quantity of hydrogel material transmit light in the first wavelength range and transmit light in the second wavelength range.

16. The method of claim 15 , wherein the fluorescent substance is not incorporated into the second quantity of hydrogel material.

17. The method of claim 15 , wherein the plurality of needle shaped wells have diameters between 175 and 225 μm and lengths between 1300 and 1500 μm.

18. The method of claim 15 , further comprising immersing the first quantity of hydrogel material and the second quantity of hydrogel material in a bath of ethanol after removing and prior to drying.

19. The method of claim 15 , wherein the first quantity of hydrogel material and the second quantity of hydrogel material have a shrinkage percentage of less than 30%.

20. The method of claim 15 , wherein the first quantity of hydrogel material and the second quantity of hydrogel material comprise a polyacrylamide hydrogel having an AAm percentage between 28 and 32 and an AAm/MBAm ratio between 14 and 16.

21. The method of claim 20 , further comprising immersing the first quantity of hydrogel material and the second quantity of hydrogel material in a bath of ethanol after removing and prior to drying.

22. The method of claim 21 , wherein the polyacrylamide hydrogel has an AAm percentage between 29 and 31 and an AAm/MBAm ratio between 14.5 and 15.5.