Blood urea nitrogen (BUN) sensor

• US 20060046275A1
• Filed: 09/01/2005
• Published: 03/02/2006
• Est. Priority Date: 09/02/2004
• Status: Active Grant

• Current Assignee: Abbott Point Of Care Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: i STAT Corporation (Abbott Laboratories Incorporated)
• Inventors: Wong, Anjulia, Brouwer, Eric, Collier, G. Bruce
• Granted Patent: US 7,540,948 B2
• Time in Patent Office: Days
• US Class Current: 435/7.900
• CPC Class Codes: C12Q 1/005 involving specific analytes or enzymes including groups of enzymes, e.g. oxydases; C12Q1/004 takes precedence
• CPC Class Codes: C12Q 1/58 involving urea or urease

Abstract

A BUN (blood urea nitrogen) sensor containing immobilized carbonic anhydrase and immobilized urease for the in vitro detection of urea nitrogen in blood and biological samples with improved performance and precision characteristics.

Claims

1. A device for detecting urea in a sample, comprising:

(a) a sensor with which a sample suspected of containing urea may be brought into contact, the sensor including at least two enzymes, urease and carbonic anhydrase immobilized on at least a portion of said sensor, and (b) a detector system for processing signals from the sensor.

2. The device of claim 1 in which said sensor comprises an ammonium ion-selective sensor.

3. The device of claim 1 in which said sensor comprises a pH sensor.

4. The device of claim 1 in which said sensor comprises a carbon dioxide or bicarbonate sensor.

5. The device of claim 1 in which said sensor comprises a conductivity sensor.

6. The device of claim 1 further comprising a second sensor without said immobilized enzymes.

7. The device of claim 1 in which said sensor is selected from the group consisting of an amperometric electrode, a potentiometric electrode, a conductimetric electrode, an optical sensor, or combinations thereof.

8. The device of claim 6 in which said second sensor is selected from the group consisting of an amperometric electrode, a potentiometric electrode, a conductimetric electrode, an optical sensor, or combinations thereof.

9. The device of claim 2 in which the ammonium ion-selective sensor includes an ammonium ionophore.

10. The device of claim 2 in which the ammonium ion-selective sensor includes nonactin.

11. The device of claim 2 in which the ammonium ion-selective sensor includes plasticized polymer.

12. The device of claim 1 in which the sensor comprises a potentiometric ammonium ion-selective electrode.

13. The device of claim 1 in which said enzymes are immobilized in a layer, said layer comprising a water-permeable matrix.

14. The device of claim 13 in which the water-permeable matrix comprises a film-forming latex.

15. The device of claim 14 in which said film-forming latex comprises a copolymer of ethylene and vinylacetate.

16. The device of claim 1 in which at least one of the enzymes is immobilized via a chemical cross-linking reagent.

17. The device of claim 1 in which at least one of the enzymes is immobilized via physical absorption.

18. The device of claim 13 in which the layer further comprises a buffer.

19. The device of claim 18 in which said buffer is selected from the group consisting of phosphate, TRIS, HEPES, or combinations thereof.

20. The device of claim 14 in which said film-forming latex includes a buffer selected from the group consisting of phosphate, TRIS, HEPES, or combinations thereof.

21. A membrane comprising a water-permeable matrix in which is included at least two enzymes, urease and carbonic anhydrase.

22. The membrane of claim 21 in which said at least two enzymes are immobilized in said water-permeable matrix.

23. The membrane of claim 21, which is in physical contact with an ion-selective electrode.

24. The membrane of claim 21, which is in physical contact with a detector.

25. The membrane of claim 21, which is physically attached to an ion-selective electrode by means of an O-ring.

26. The membrane of claim 21, which is attached to a fixture capable of mating with an ion-selective electrode.

27. The membrane of claim 21, which is formed by applying a liquid mixture onto a surface and allowing said liquid mixture to dry on said surface.

28. The membrane of claim 27, which forms a component of a urea detecting device.

29. The membrane of claim 28 in which the urea detecting device is selected from the group consisting of an amperometric electrode, a potentiometric ion-selective electrode, an optical sensor, a conductimetric electrode, or combinations thereof.

30. The membrane of claim 28 in which the urea detecting device comprises a microfabricated sensor.

31. The membrane of claim 30 in which the microfabricated sensor comprises an ion-selective electrode.

32. The membrane of claim 30 in which the microfabricated sensor is responsive to ammonium ions.

33. The membrane of claim 21 in which said water-permeable membrane is latex.

34. The membrane of claim 21 comprising a polymer selected from the group consisting of cellulose acetate, nitrocellulose, polyurethane, bovine serum albumin cross-linked by glutaraldehyde, acrylamide, cellophane, film-forming latex, or mixtures thereof.

35. A device for detecting urea in a sample comprising an electrode coated with a first layer, said first layer comprising plasticized polymer, ammonium ionophore, and at least two enzymes, urease and carbonic anhydrase, immobilized on said first layer.

36. A device for detecting urea in a sample comprising an electrode coated with a first layer, said first layer comprising plasticized polymer and ammonium ionophore, and a second layer positioned over and contacting at least a portion of said first layer, said second layer comprising a water-permeable matrix in which is included at least two enzymes, urease and carbonic anhydrase.

37. The device of claim 36 in which said at least two enzymes are immobilized in said water-permeable matrix.

38. A microfabricated sensing device for detecting urea in a sample comprising:

(a) a substantially planar substrate having a patterned microelectrode surface,

(b) a first layer over at least a portion of said substrate comprising a plasticized polymer and nonactin, and

(c) a second layer positioned over at least a portion of said first layer, comprising a water-permeable matrix in which is included at least two enzymes, urease and carbonic anhydrase.

39. The microfabricated sensing device of claim 38 in which said polymer is polyvinylchloride.

40. The device of claim 38 in which said patterned microelectrode surface establishes a potential in response to the presence of ammonium ions.

41. The device of claim 38 in which said at least two enzymes are immobilized in said water-permeable matrix.

42. The device of claim 38 in which said first and second layers are microdispensed.

43. An improved ion-selective sensor for detection of urea having a layer in which is immobilized an enzyme, urease, the improvement comprising:

immobilizing at least one other enzyme, carbonic anhydrase, in said layer.

44. A method for assaying urea in a sample, comprising:

contacting a sample suspected of containing urea with a sensor having at least two immobilized enzymes, urease and carbonic anhydrase, and

detecting a chemical moiety with a sensor selected from the group consisting of an ammonium ion sensor, a pH sensor, a carbon dioxide sensor, a bicarbonate sensor, a conductivity sensor, or combinations thereof.

45. The method of claim 44 in which said chemical moiety is ammonium ion.

46. The method of claim 45 in which the amount of ammonium ion detected is a function of the amount of urea in the sample.

47. The method of claim 46 in which said sensor is potentiometric and said function is substantially logarithmic.

48. The method of claim 44 in which said sensor is calibrated by exposing said sensor to an aqueous fluid, which contains a known amount of ammonium ion, before or after said sample is contacted with the sensor.

49. A method for improving the sensitivity of a urea sensor, which sensor comprises a detector and an immobilized enzyme, urease, the method comprising:

adding an effective amount of a second immobilized enzyme, carbonic anhydrase, to said sensor.

50. The method of claim 49 in which said detector comprises an ammonium ion-selective sensor.

51. The method of claim 49 in which said detector comprises a pH sensor.

52. The method of claim 49 in which said detector comprises a carbon dioxide sensor or a bicarbonate sensor.

53. The method of claim 49 in which said detector comprises a conductivity sensor.

54. The method of claim 49 in which a second detector without said enzymes is used to measure a difference signal.