Implantable biosensor system, apparatus and method

Abstract

An implantable biosensor assembly and system includes an enzymatic sensor probe from which subcutaneous and interstitial glucose levels may be inferred. The assembly may be associated by direct percutaneous connection with electronics, such as for signal amplification, sensor polarization, and data download, manipulation, display, and storage. The biosensor comprises a miniature probe characterized by lateral flexibility and tensile strength and has a large electrode surface area for increased sensitivity. Irritation of tissues surrounding the probe is minimized due to ease of flexibility and small cross section of the sensor. Foreign body reaction is diminished due to a microscopically rough porous probe surface.

1 . An implantable needle-type biosensor wherein an electric signal is produced between first and second electrical contacts responsive to an electrochemical reaction in a body, said biosensor comprising: 
 an elongate core comprising a plurality of axially oriented fibers, said elongate core having a distal end and a proximal end, said distal end being spaced apart in an axial direction from said proximal end;    a working electrode associated with said distal end;    a reference electrode spaced apart from said working electrode;    structure adapted to resist direct physical contact between said working electrode and said reference electrode;    a first electrically conductive path between said working electrode and said first electrical contact; and    a second electrically conductive path between said reference electrode and said second electrical contact.    
     
     
         2 . The implantable needle-type biosensor of  claim 1 , wherein said working electrode comprises a metal element formed as a wrap about a portion of said core.  
     
     
         3 . The implantable needle-type biosensor of  claim 1 , wherein said working electrode comprises a length of a first wire arranged to circumscribe a plurality of revolutions about said core.  
     
     
         4 . The implantable needle-type biosensor of  claim 3 , wherein said first wire's diameter is between about 0.001 and about 0.005 inches.  
     
     
         5 . The implantable needle-type biosensor of  claim 1 , wherein said working electrode comprises a first wire arranged to form a spiral path.  
     
     
         6 . The implantable needle-type biosensor of  claim 5 , wherein said spiral path has an axial pitch spacing, between centerlines of a pair of adjacent wire wraps, sized between about one and about four diameters of said first wire.  
     
     
         7 . The implantable needle-type biosensor of  claim 1 , wherein said working electrode is arranged in harmony with said core to form a reinforced core operable to carry an axial compression load permitting insertion of a distal tip of said biosensor through an introducer catheter for placement of said working electrode into intimate contact with tissue of the body.  
     
     
         8 . The implantable needle-type biosensor of  claim 1 , wherein said reference electrode is associated with said distal end and comprises a length of a second wire formed as a wrap about a portion of said core.  
     
     
         9 . The implantable needle-type biosensor of  claim 8 , further comprising: 
 a dielectric spacer interposed between said working electrode and said reference electrode to resist direct physical contact therebetween.    
     
     
         10 . The implantable needle-type biosensor of  claim 1 , wherein said core comprises an electrically nonconductive material.  
     
     
         11 . The implantable needle-type biosensor of  claim 10 , wherein said core comprises a polymer material.  
     
     
         12 . The implantable needle-type biosensor of  claim 1 , further comprising: 
 a sensor shaft disposed between said working electrode and a hub, said shaft comprising a cylinder disposed circumferentially about an axial length of said core proximal to said working electrode.    
     
     
         13 . The implantable needle-type biosensor of  claim 1 , wherein said working electrode comprises an exterior coating of a negatively charged polymer.  
     
     
         14 . The implantable needle-type biosensor of  claim 13 , wherein said negatively charged polymer comprises sulfonated polyethersulfone.  
     
     
         15 . The implantable needle-type biosensor of  claim 1 , wherein said reference electrode and said working electrode are both arranged for disposition in intimate contact with tissues of a subject.  
     
     
         16 . An implantable biosensor, comprising: 
 an introducer cannula with a lumen extending axially between proximal and distal ends, said proximal end carrying affixing structure adapted to resist motion of said proximal end relative to a skin surface of a subject and further carrying holding structure configured to receive a probe;    said probe structured for sliding installation of a distal probe end through said lumen, said probe comprising an elongate core having a distal end spaced apart axially from a proximal end, a proximal end of said probe being associated with a hub adapted for attachment to said holding structure;    a first electrode associated with said distal end of said probe; and    a second electrode associated with said distal end of said cannula, said cannula and said probe being cooperatively structured on assembly to resist direct physical contact between said first electrode and said second electrode.    
     
     
         17 . The implantable biosensor of  claim 16 , wherein said reference and said working electrodes are both arranged for disposition in intimate contact with tissue of a subject.  
     
     
         18 . A method for manufacturing an implantable, needle-type biosensor probe with a transversely flexible first electrode effective to resist irritation at a site of implantation in a subject, the method comprising: 
 providing a core comprising a first nonconductive material;    disposing a first electrode in a reinforcing path about said core;    disposing structure forming a first electrical conductor between said first electrode and a hub associated with a proximal end of said probe; and    disposing structure forming a second electrical conductor between a second electrode and said hub.    
     
     
         19 . The method of  claim 18 , further comprising: 
 forming said first electrode from a first wire, a diameter of said first wire being between about 0.001 and about 0.005 inches; and    disposing said first wire in a spiral path about said core.