Small volume in vitro analyte sensor and methods

Abstract

A small volume sensor, and methods of making, for determining the concentration of an analyte, such as glucose or lactate, in a biological fluid such as blood or serum, using techniques such as coulometry, amperometry, and potentiometry. The sensor includes a working electrode and a counter electrode, and can include an insertion monitoring trace to determine correct positioning of the sensor in a connector. In one embodiment, the sensor determines the concentration of the analyte by discharging an amount of charge into the sample, determining the time needed to discharge the charge, and determining the current used to electrolyze a portion of the analyte using the amount of charge and the amount of time.

We claim:  
     
         1 . A sample acquisition apparatus for piercing skin, the apparatus comprising 
 a skin piercing lancet,    a cocking mechanism operable connected to the skin piercing lancet, the cocking mechanism configured to move the lancet from an inactivated position to a cocked position;    a triggering mechanism operably connected to the spin piercing lancet, the trigger mechanism configured to release the lancet from the cocked position to a protruding position; and    a cap having a protruding ring with a surface area, the protruding ring defining a center for passing the lancet therethrough, the surface area configured for contact with the skin.    
     
     
         2 . The sample acquisition apparatus according to  claim 1  further comprising a depth adjustment mechanism for adjusting the depth of the penetration of the lancet into the skin when in the protruding position.  
     
     
         3 . The sample acquisition apparatus according to  claim 1  wherein the cocking mechanism requires active cocking.  
     
     
         4 . The sample acquisition apparatus according to  claim 1  wherein the surface area is an annular surface area.  
     
     
         5 . A method of lancing a patient's skin, the method comprising: 
 (a) providing a sample acquisition apparatus comprising a skin piercing lancet and a cap having a protruding ring with a surface area, the protruding ring defining a center for passing the lancet therethrough, the surface area configured for contact with the skin.    (b) cocking the lancet with a cocking mechanism, thereby moving the lancet from an inactivated position to a cocked position;    (c) after cocking the lancet, contacting the skin with the protruding ring; and    (d) triggering the lancet with a triggering mechanism, thereby releasing the lancet from the cocked position to a protruding position and piercing the skin with the lancet.    
     
     
         6 . The method according to  claim 5 , further comprising: 
 (a) controlling the depth of the lancet in the protruding position by adjusting a depth adjustment mechanism.    
     
     
         7 . The method according to  claim 5  wherein the step of contacting the skin with the protruding ring comprises: 
 (a) increasing the tension on the skin.  
 
     
     
         8 . The method according to  claim 7  wherein the step of increasing the tension on the skin comprises: 
 (a) increasing the tension on the skin to form a bump.  
 
     
     
         9 . The method according to  claim 7  wherein the step of increasing the tension on the skin comprises: 
 (a) increasing the tension on the skin to extend the skin.  
 
     
     
         10 . The method according to  claim 5 , wherein the method comprises: 
 (a) lancing the skin on a patient's arm or thigh.    
     
     
         11 . The method according to  claim 5 , wherein after piercing the skin with the lancet, the method comprises: 
 (a) obtaining a blood sample having a volume no more than about 1 μL.    
     
     
         12 . The method according to  claim 11 , wherein the step of obtaining a blood sample comprises: 
 (a) obtaining a blood sample having a volume no more than about 0.5 μL.    
     
     
         13 . The method according to  claim 11 , wherein the step of obtaining a blood sample comprises: 
 (a) obtaining a blood sample having a volume no more than about 0.25 μL.