Diffusion layer for an enzymatic in vivo sensor

• US 10,422,765 B2
• Filed: 09/16/2013
• Issued: 09/24/2019
• Est. Priority Date: 03/28/2011
• Status: Active Grant

• Current Assignee: Roche Diabetes Care Inc. (Roche Holding AG)
• Original Assignee: Roche Diabetes Care Inc. (Roche Holding AG)
• Inventors: Staib, Arnulf, Thiele, Marcel, Koelker, Karl-Heinz, Rieger, Ewald
• Primary Examiner(s): Mallari, Patricia
• Assistant Examiner(s): Tran, Tho Q
• Application Number:
  US14/027,493
• Publication Number:
  US 20140018653A1
• Time in Patent Office: 2,199 Days
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1486 using enzyme electrodes, e.g. with immobilised oxidase
• CPC Class Codes: A61B 5/14865 invasive, e.g. introduced into the body by a catheter or needle or using implanted sensors
• CPC Class Codes: C12Q 1/002 Electrode membranes
• CPC Class Codes: C12Q 1/006 for glucose
• CPC Class Codes: G01N 27/3271 Amperometric enzyme electrodes for analytes in body fluids, e.g. glucose in blood amperometry per se G01N27/49; aspects concerning the enzyme reagent C12Q1/001
• CPC Class Codes: G01N 27/3272 Test elements therefor, i.e. disposable laminated substrates with electrodes, reagent and channels optical biosensors G01N33/52

Abstract

Electrode systems are disclosed for measuring the concentration of an analyte under in vivo conditions, where the systems includes an electrode with immobilized enzyme molecules and an improved diffusion barrier that controls diffusion of the analyte from body fluid surrounding the electrode system to the enzyme molecules. Methods of making and using the system also are disclosed.

Claims

1. An electrode system for measuring the concentration of an analyte under in vivo conditions, the system comprising:

an electrode with immobilized enzyme molecules; and

a diffusion barrier that controls diffusion of the analyte from an exterior of the electrode system to the immobilized enzyme molecules, wherein the diffusion barrier comprises a block copolymer having at least one hydrophilic block and at least one hydrophobic block, wherein the at least one hydrophilic block is made from hydrophilic monomeric units selected from the group consisting of hydrophilic (meth)acrylesters with a polar —

OH, —

OCH₃ or —

OC₂H₂ group, hydrophilic (meth)acrylamides, (meth)acrylic acid, and combinations thereof, wherein the at least one hydrophilic block and the at least one hydrophobic block are covalently linked to one another, and wherein the at least one hydrophobic block has a glass transition temperature between 40°

C. and 100°

C.

2. The electrode system of claim 1, wherein:

(i) the at least one hydrophilic block of the block copolymer has a length selected from the group consisting of from about 50 to about 200 monomeric units, from about 150 to about 300 monomeric units, from about 100 to about 150 monomeric units, and from about 200 to about 250 monomeric units; and

/or

(ii) the at least one hydrophobic block of the block copolymer has a length selected from the group consisting of from about 50 to about 200 monomeric units, from about 150 to about 250 monomeric units, from about 80 to about 150 monomeric units, and from about 170 to about 200 monomeric units.

3. The electrode system of claim 1, wherein (i) if the hydrophilic monomeric units for the at least one hydrophilic block are hydrophilic (meth)acrylesters with a polar —

OH, —

OCH₃ or —

OC₂H₂ group, they are selected from the group consisting of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate (HEMA), 2-methoxyethyl acrylate, 2-methoxyethyl methacrylate, 2-ethoxyethyl acrylate, 2-ethoxyethyl methacrylate, 2- or 3-hydroxypropyl acrylate, 2- or 3-hydroxypropyl methacrylate (2- or 3-HPMA), 2- or 3-methoxypropyl acrylate, 2- or 3-methoxypropyl methacrylate, 2- or 3-ethoxypropyl acrylate, 2- or 3-ethoxypropyl methacrylate, 1- or 2-glycerol acrylate, 1- or 2-glycerol methacrylate, (ii) if the hydrophilic monomeric units for the at least one hydrophilic block are hydrophilic (meth)acrylamides, then they are selected from the group consisting of acrylamide, methacrylamide, an N-alkyl- or N,N-dialkyl acrylamide, and an N-alkyl- or N,N-dialkyl methylamide wherein the alkyl comprises 1-3 C-atoms, (iii) if the hydrophilic monomeric units for the at least one hydrophilic block are (meth)acrylic acid, they are selected from the group consisting of acrylic acid, methacrylic acid, and (iv) combinations of (i) to (iii).

4. The electrode system of claim 1, wherein the at least one hydrophilic block comprises at least two different hydrophilic monomeric units, wherein at least one of the hydrophilic monomeric units is a non-ionic hydrophilic monomeric unit and at least one of the hydrophilic monomeric units is an ionic hydrophilic monomeric unit, and wherein the ionic hydrophilic monomeric unit is present in a molar amount of from about 1 mol-% to about 20 mol-%.

5. The electrode system of claim 1, wherein the at least one hydrophobic block is made from monomeric units selected from the group consisting of hydrophobic (meth)acrylesters, styrene-based monomers, and combinations thereof.

6. The electrode system of claim 5, wherein if the hydrophobic monomeric units for the at least one hydrophobic block are (meth)acrylesters, they are selected from the group consisting of methyl acrylate, methyl methacrylate (MMA), ethyl acrylate, ethyl methacrylate (EMA), n- or i-propyl acrylate, n- or i-propyl methacrylate, n-butyl acrylate, n-butyl methacrylate (BUMA), neopentyl acrylate, neopentyl methacrylate, and combinations thereof.

7. The electrode system of claim 1, wherein the at least one hydrophobic block comprises at least two different hydrophobic monomeric units.

8. The electrode system of claim 7, wherein the at least one hydrophobic block has a glass transition temperature of about 40°

C. to about 80°

C.

9. The electrode system of claim 1, wherein the molar ratio of hydrophilic block:

hydrophobic block is in a range selected from the group consisting of about 75% (hydrophilic);

25% (hydrophobic) to about 25% (hydrophilic);

75% (hydrophobic), from about 65% (hydrophilic);

35% (hydrophobic) to about 35% (hydrophilic);

65% (hydrophobic), and from about 60% (hydrophilic);

40% (hydrophobic) to about 40% (hydrophilic);

60% (hydrophobic).

10. The electrode system of claim 1 further comprising:

a counter electrode having an electrical conductor; and

a working electrode having an electric conductor on which the immobilized enzyme molecules and the diffusion barrier are arranged.

11. The electrode system of claim 10, wherein the immobilized enzyme molecules are present in the form of multiple fields arranged on the conductor of the working electrode at a distance from each other.

12. The electrode system of claim 1, wherein the diffusion barrier forms a layer covering an enzyme layer with a thickness selected from the group consisting of about 2 μ

m to about 20 μ

m, of about 5 μ

m to about 20 μ

m, and of about 10 μ

m to about 15 μ

m.

13. The electrode system of claim 1, wherein an enzyme layer and the diffusion barrier are covered by a spacer, and wherein the spacer is a copolymer of (meth)acrylates comprising more than 50 mol-% hydrophilic monomeric units.

14. The electrode system of claim 1, wherein the diffusion barrier comprises only one block copolymer.

15. The electrode system of claim 1, wherein the diffusion barrier further comprises a plasticizer.

16. The electrode system of claim 1, wherein the diffusion barrier has an effective diffusion coefficient (D_eff) for glucose selected from the group consisting of ≥

10<sup>−

10</sup> cm²/s, ≥

5·

10<sup>−

10</sup> cm²/s, and ≥

10<sup>−

9</sup> cm²/s.

17. An insertable or implantable sensor configured for measuring glucose, the sensor comprising:

a flexible and biocompatible substrate;

the electrode system of claim 1 applied on the substrate;

a potentiostat applied on the substrate and in electrical communication with the electrode system; and

an amplifier applied on the substrate and in electrical communication with the electrode system for amplifying measuring signals of the electrode system,

wherein the immobilized enzyme molecules are glucose oxidase or glucose dehydrogenase.

20. The electrode system of claim 7, wherein the at least two different hydrophobic monomeric units are randomly arranged in the at least one hydrophobic block.

21. The electrode system of claim 7, wherein the at least one hydrophilic block is 2-hydroxyethyl methacrylate (HEMA), and wherein the at least one hydrophobic block is methyl methacrylate (MMA) and n-butyl methacrylate (BUMA).

24. The electrode system of claim 1 wherein the at least one hydrophobic block is made from hydrophobic monomeric units selected from the group consisting of hydrophobic (meth)acrylesters, styrene-based monomers and combinations thereof.

18. A method of making a diffusion barrier for an enzymatic electrode, the method comprising the steps of:

providing a solution of block copolymer in a solvent or a solvent mixture to a prefabricated electrode system having the enzymatic electrode, wherein the block copolymer comprises at least one hydrophilic block and at least one hydrophobic block covalently linked to one another as the block copolymer, and wherein the at least one hydrophilic block is made from hydrophilic monomeric units selected from the group consisting of hydrophilic (meth)acrylesters with a polar —

OH, —

OCH₃ or —

OC₂H₂ group, hydrophilic (meth)acrylamides, (meth)acrylic acid, and combinations thereof; and

drying the solution into the diffusion barrier for the enzymatic electrode, wherein the at least one hydrophobic block has a glass transition temperature between 40°

C. and 100°

C.

19. The method of claim 18, wherein:

(i) the at least one hydrophilic block of the block copolymer has a length selected from the group consisting of from about 50 to about 200 monomeric units, from about 150 to about 300 monomeric units, from about 100 to about 150 monomeric units, and from about 200 to about 250 monomeric units; and

/or

(ii) the at least one hydrophobic block of the block copolymer has a length selected from the group consisting of from about 50 to about 200 monomeric units, from about 150 to about 250 monomeric units, from about 80 to about 150 monomeric units, and from about 170 to about 200 monomeric units.

22. The method of claim 18, wherein the at least one hydrophobic block comprises at least two different hydrophobic monomeric units that are randomly arranged.

23. The method of claim 22, wherein the at least one hydrophilic block is 2-hydroxyethyl methacrylate (HEMA), and wherein the at least one hydrophobic block is methyl methacrylate (MMA) and n-butyl methacrylate (BUMA).

25. An electrode system for measuring the concentration of an analyte under in vivo conditions, the system comprising:

an electrode with immobilized enzyme molecules; and

a diffusion barrier that controls diffusion of the analyte from an exterior of the electrode system to the immobilized enzyme molecules, wherein the diffusion barrier comprises a block copolymer having at least one hydrophilic block and at least one hydrophobic block, wherein the at least one hydrophilic block is made from hydrophilic monomeric units selected from the group consisting of hydrophilic (meth)acrylesters with a polar —

OH, —

OCH₃ or —

OC₂H₂ group, hydrophilic (meth)acrylamides, (meth)acrylic acid, and combinations thereof, wherein the at least one hydrophilic block and the at least one hydrophobic block are covalently linked to one another, and wherein the at least one hydrophobic block is made from hydrophobic monomeric units selected from the group consisting of hydrophobic (meth)acrylesters, styrene-based monomers and combinations thereof.