System and method for diagnosing sensor performance using analyte-independent ratiometric signals

Abstract

A system and method are provided for utilizing radiometric fluorescence detection to determine a glucose independent concentration value when measuring frequency bands that do not contain the system isosbestic point. Preferably two bands are chosen such that a first band is below the system isosbestic point, and a second band is above the system isosbestic point, and both points are sufficiently far from the frequency endpoints to maximize the signal to noise ratio.

What is claimed is: 
     
         1 . A method of performing a diagnostic test on an analyte sensor, comprising the steps of:
 introducing matrix suspended analyte binding protein to an analyte environment, said binding protein labeled with a dye fluorescing with an intensity spectrum related to a concentration of said analyte concentration in said environment;   measuring a first fluorescent intensity at a first frequency component that is higher than an isosbestic frequency of the dye;   measuring a second fluorescent intensity at a second frequency component that is lower than the isosbestic frequency;   determining a GIIC value based on the first and second fluorescent intensities;   diagnosing a performance of said analyte sensor based on said determination.   
     
     
         2 . The method of  claim 1 , wherein the analyte binding protein is a glucose binding protein. 
     
     
         3 . The method of  claim 1 , wherein said analyte is glucose. 
     
     
         4 . The method of  claim 1 , wherein a ratio between the first frequency component and the second frequency component for the dye is defined by:
     R =( R 0 +Rinf ([ G]/KD ))/(1+[ G ]/ KD )   where   [G] is the analyte concentration;   R is the ratio at a given analyte concentration;   R0 is the ratio of spectral bands at zero analyte concentration;   Rinf is the ratio of spectral bands at infinite (saturating) analyte concentration; and   KD is an apparent dissociation constant for the system.   
     
     
         5 . The method of  claim 4 , wherein the analyte is glucose, and [G] is the glucose concentration. 
     
     
         6 . The method of  claim 4 , wherein a glucose independent intensity is calculated according to the following equation:
     GII =( KDg/KDb −1)* Fb*Fg+Fb* ( Fginf −( KDg/KDb )* Fg 0)+ Fg ( Fb 0−( KDg/KDb )* Fbinf )
   where   GII is the glucose independent intensity;   Fb is the measured intensity of the first frequency component;   Fg is the measured intensity of the second frequency component;   KDg is the dissociation constant determined when using only the second frequency component;   KDb is the dissociation constant determined when using only the first frequency component;   Fginf is the intensity of the second frequency component at saturated concentration;   Fg0 is the intensity of the second frequency component at zero concentration;   Fbinf is the intensity of the first frequency component at saturated concentration; and   Fb0 is the intensity of the first frequency component at zero concentration.   
     
     
         7 . The method of  claim 1 , wherein a computing architecture that processes a raw sensor signal also calculates analyte concentration. 
     
     
         8 . The method of  claim 1 , wherein the first frequency component and the second frequency component are selected to be far from the isosbestic frequency but closer than frequencies at which the signal to noise ratio drops below 10% of the maximum signal to noise ratio. 
     
     
         9 . The method of  claim 1 , wherein the first fluorescent intensity is generated by a first dye and the second fluorescent intensity is generated by a second dye.