ENHANCED GLUCOSE LIMITING MEMBRANE FOR A WORKING ELECTRODE OF A CONTINUOUS BIOLOGICAL SENSOR
Briefly, a sensor for a continuous biological monitor is provided that has a working electrode with a new interfere layer that is (1) non-electron conducting, (2) ion passing, and (3) permselective for molecular weight. The new interference layer is made by mixing a monomer and a mildly basic buffer, and then electropolymerizing the monomer and the buffer into a polymer. The polymer is deposited onto a working electrode for a continuous metabolic monitor, for example, using an electro depositing process in the form of cyclic voltammety (CV). The interference layer is permselectable for molecule size by adjusting the pH of the basic buffer.
1 . A working electrode for a subcutaneous sensor for use with a continuous metabolic monitor for a patient, comprising:
a conductive substrate;
an enzyme membrane comprising an enzyme selected for a target metabolic function; and
a glucose limiting layer over the enzyme membrane that limits the amount of glucose from a patient's blood that passes to the enzyme layer, the glucose limiting layer comprising a hydrophobic material that is physically cross linked to a hydrophilic material.
2 . The working electrode according to claim 1 , wherein the physical cross linking is in the form of hydrogen bonds.
3 . The working electrode according to claim 1 , wherein the hydrophobic material comprises polyurethane or silicone.
4 . The working electrode according to claim 1 , wherein the hydrophilic material comprises Polyvinylpyrrodlidone (PVP).
5 . The working electrode according to claim 1 , further comprising a hydrogen peroxide generating membrane between the enzyme layer and the conductive substrate, the hydrogen peroxide membrane having a band, window or opening that permits hydrogen peroxide molecules to pass from the enzyme membrane to the conductive substrate.
6 . The working electrode according to claim 1 , further comprising a hydrogen peroxide membrane between the enzyme layer and the conductive substrate, the hydrogen peroxide membrane being continuous and permitting hydrogen peroxide molecules to pass through it from the enzyme membrane to the conductive substrate.
7 . The working electrode according to claim 1 , wherein the glucose limiting membrane is formed to transfer less than 1 per 400 molecules of glucose from the patient's blood or ISF.
8 . A method of making a glucose limiting layer for a working electrode of a continuous biological monitor, comprising:
mixing a hydrophilic material, a hydrophobic material and a solvent to form a bonding gel;
applying the bonding gel to the working electrode; and
curing the bonding gel to form physical cross linking between the hydrophobic and hydrophilic materials.
9 . The method according to claim 8 , wherein the cross linking is in the form of hydrogen bonds.
10 . The method according to claim 8 , wherein the hydrophobic material is biocompatible.
11 . The method according to claim 8 , wherein the hydrophobic material is polyurethane or silicone.
12 . The method according to claim 8 , wherein the hydrophilic material has a molecular weight over 1M.
13 . The method according to claim 8 , wherein the hydrophilic material has a molecular weight in the range of about 1M to about 3M.
14 . The method according to claim 8 , wherein the hydrophilic material is Polyvinylpyrrodlidone (PVP).
15 . The method according to claim 8 , wherein the solvent is polar, binary, and volatile.
16 . The method according to claim 8 , wherein the solvent comprises a heavy organic compound mixed with an alcohol.
17 . The method according to claim 8 , wherein the solvent comprises tetrahydrofuan (THF) or Dimethylformamide (DMF).
18 . The method according to claim 8 , wherein the solvent comprises ethanol.
19 . The method according to claim 8 , wherein the applying step comprises dipping, spraying, depositing, printing, or pad printing.
20 . The method according to claim 8 , wherein the curing step comprises moving air, heat or applying a vacuum.
21 . The method according to claim 8 , wherein working electrode is in the form of a wire.