Amperometric sensor and method for its manufacturing

Abstract

An in vivo amperometric sensor is provided for measuring the concentration of an analyte in a body fluid. The sensor comprises a counter electrode and a working electrode, and the working electrode comprises a sensing layer which is generally water permeable and arranged on a support member adjacent to a contact pad. The sensing layer comprises an immobilized enzyme capable of acting catalytically in the presence of the analyte to cause an electrical signal. The sensing layer has an upper surface facing the body fluid and a lower surface facing away from the body fluid, and the immobilized enzyme is distributed within the sensing layer in such a way that the enzyme concentration in the middle between the upper and lower surfaces is at least as high as on the upper surface of the sensing layer.

1 - 32 . (canceled) 
     
     
         33 . A method of using an in vivo amperometric biosensor of the type having working and counter electrodes arranged on a support member, the working electrode having a sensing layer with immobilized enzyme distributed therein, the method comprising:
 implanting the sensor into a body part to bring the sensing layer into contact with body fluid having an analyte; and   controlling the rate of analyte diffusion through the sensor so that diffusion of the analyte in the sensing layer is the rate-limiting step in generating a signal corresponding to analyte concentration.   
     
     
         34 . The method of  claim 33 , further comprising providing the sensing layer with an effective diffusion coefficient D eff  of analyte through the sensing layer of about 10-times to about 1000-times lower than the coefficient D of the analyte in water. 
     
     
         35 . The method of  claim 33 , further comprising providing a diffusion barrier above the sensing layer, wherein the diffusion barrier inhibits diffusion of analyte into the sensor to the extent that analyte concentration at the upper surface of the sensing layer is at most about ten times lower than in the body fluid surrounding the implanted sensor. 
     
     
         36 . The method of  claim 33 , further comprising arranging the biosensor so that the sensing layer has an upper surface facing the body fluid and facing away from the support member and a lower surface facing away from the body fluid and facing toward the support member. 
     
     
         37 . The method of  claim 33 , wherein, after the implanting, the analyte concentration at the upper surface of the sensing layer is at most about 10 times lower than in the body fluid surrounding the sensor. 
     
     
         38 - 53 . (canceled)