Small Volume In Vitro Analyte Sensor

Abstract

A sensor utilizing a non-leachable or diffusible redox mediator is described. The sensor includes a sample chamber to hold a sample in electrolytic contact with a working electrode, and in at least some instances, the sensor also contains a non-leachable or a diffusible second electron transfer agent. The sensor and/or the methods used produce a sensor signal in response to the analyte that can be distinguished from a background signal caused by the mediator. The invention can be used to determine the concentration of a biomolecule, such as glucose or lactate, in a biological fluid, such as blood or serum, using techniques such as coulometry, amperometry, and potentiometry. An enzyme capable of catalyzing the electrooxidation or electroreduction of the biomolecule is typically provided as a second electron transfer agent.

1 - 18 . (canceled) 
     
     
         19 . A sensor comprising:
 a working electrode and a counter electrode separated from one another in a range of 25 μm to 1000 μm;   a sample chamber for holding a sample fluid, the working electrode and the counter electrode being located in the sample chamber, and the sample chamber being sized to contain a volume of no more than about 1 μL of the sample fluid;   first and second apertures defined upon the sample chamber; and   an analyte-responsive enzyme and a redox mediator disposed within the sample chamber;
 wherein the redox mediator comprises a transition metal complex comprising a heterocyclic nitrogen ligand. 
   
     
     
         20 . The sensor of  claim 19 , further comprising:
 first and second indicator electrodes located within the sample chamber, the first indicator electrode being positioned to indicate when the sample fluid begins to fill the sample chamber and the second indicator electrode being positioned to indicate when the sample chamber is substantially filled with the sample fluid;
 wherein the working electrode is disposed between the first and second indicator electrodes. 
   
     
     
         21 . The sensor of  claim 19 , wherein the redox mediator is diffusible within the sample chamber. 
     
     
         22 . The sensor of  claim 21 , wherein the redox mediator is disposed upon the working electrode. 
     
     
         23 . The sensor of  claim 19 , wherein the redox mediator is immobilized upon the working electrode within the sample chamber. 
     
     
         24 . The sensor of  claim 23 , wherein the analyte-responsive enzyme is immobilized upon the working electrode within the sample chamber. 
     
     
         25 . The sensor of  claim 23 , wherein the transition metal complex comprises two or more ligands that are coordinatively bound to a transition metal, and at least one of the two or more ligands is a bidentate ligand comprising a heterocyclic nitrogen compound. 
     
     
         26 . The sensor of  claim 25 , wherein the transition metal is selected from the group consisting of osmium, ruthenium, iron, and cobalt. 
     
     
         27 . The sensor of  claim 25 , wherein the bidentate ligand has a structure of 
       
         
           
           
               
               
           
         
         wherein R 1  is selected from the group consisting of hydrogen, hydroxy, alkyl, alkoxy, alkenyl, vinyl, allyl, amido, amino, vinylketone, a keto-containing group, and a sulfur-containing group. 
       
     
     
         28 . The sensor of  claim 19 , wherein the transition metal complex comprises a transition metal selected from the group consisting of osmium, ruthenium, iron, and cobalt. 
     
     
         29 . The sensor of  claim 19 , wherein the transition metal complex comprises two or more ligands that are coordinatively bound to a transition metal, at least one of the two or more ligands is a bidentate ligand comprising a heterocyclic nitrogen compound, and at least one of the two or more ligands is a monosubstituted pyridine compound. 
     
     
         30 . The sensor of  claim 29 , wherein the transition metal is selected from the group consisting of osmium, ruthenium, iron, and cobalt. 
     
     
         31 . The sensor of  claim 29 , wherein the bidentate ligand has a structure of 
       
         
           
           
               
               
           
         
         wherein R 1  is selected from the group consisting of hydrogen, hydroxy, alkyl, alkoxy, alkenyl, vinyl, allyl, amido, amino, vinylketone, a keto-containing group, and a sulfur-containing group. 
       
     
     
         32 . The sensor of  claim 19 , wherein the working electrode and the counter electrode are in a facing configuration. 
     
     
         33 . The sensor of  claim 19 , further comprising:
 a first substrate having a proximal end and a distal end, the first substrate defining a first side edge and a second side edge extending from the proximal end to the distal end of the first substrate;   a second substrate disposed over the first substrate, the working electrode being disposed on one of the first and second substrates and the counter electrode being disposed on one of the first and second substrates; and   a spacer disposed between the first and second substrates, the spacer defining the first aperture along the first side edge of the sensor and the second aperture along the second side edge of the sensor, the sample chamber extending from the first aperture to the second aperture.   
     
     
         34 . The sensor of  claim 19 , further comprising
 a first substrate having a proximal end and a distal end, the first substrate defining a first side edge and a second side edge extending from the proximal end to the distal end of the first substrate;   a second substrate disposed over the first substrate, the working electrode being disposed on one of the first and second substrates and the counter electrode being disposed on one of the first and second substrates; and   a spacer disposed between the first and second substrates, the spacer defining the first aperture along the proximal end of the sensor and the second aperture along the first side edge of the sensor, the sample chamber extending from the first aperture to the second aperture.   
     
     
         35 . The sensor of  claim 19 , wherein the enzyme is a glucose-responsive enzyme or a lactate-responsive enzyme. 
     
     
         36 . The sensor of  claim 19 , further comprising:
 a sorbent material located within the sample chamber.