Determining usability of analytical test strip

Abstract

A system for determining usability of an analytical test strip includes a sample chamber to receive a fluid sample, a reagent in the sample chamber having a moisture-varying impedance, and two detection electrodes contacting the reagent. A test meter applies an AC waveform across the reagent via the detection electrodes while measuring an impedance of the reagent. A processor automatically determines whether the measured impedance of the reagent meets a dryness criterion. The meter includes a housing, a strip port connector, an impedance measurement circuit and the processor. A method for determining usability of a strip inserted in a hand held meter includes applying an AC waveform across a reagent of the strip and measuring a first electrical signal, and determining whether the strip meets the dryness criterion based on the first electrical signal. The test strip and ways of determining an analyte are also described.

What is claimed is: 
     
         1 . A system for determining usability of an analytical test strip, the system comprising:
 a) the analytical test strip having a sample chamber adapted to receive a fluid sample, a reagent arranged at least partly in the sample chamber, and two spaced-apart detection electrodes in contact with the reagent, wherein the reagent has an impedance that varies with moisture content; and   b) a test meter adapted to receive the analytical test strip, the test meter having an impedance-measurement circuit configured to apply an alternating-current waveform across the reagent via the detection electrodes and concurrently measure an impedance of the reagent, and having a processor configured to automatically determine whether the measured impedance of the reagent meets a selected dryness criterion.   
     
     
         2 . The system according to  claim 1 , wherein the test meter further includes a user interface, wherein the processor is configured to, if the measured impedance does not meet the selected dryness criterion, present an error indication via the user interface. 
     
     
         3 . The system according to  claim 1 , wherein the analytical test strip further includes a sample electrode arranged at least partly in the sample chamber and the test meter further includes an analyte measurement circuit electrically connected to the sample electrode and at least one of the spaced-apart detection electrodes. 
     
     
         4 . The system according to  claim 3 , wherein the processor is further configured to, if the measured impedance of the reagent meets the dryness criterion, detect the presence of the fluid sample in the sample chamber of the received analytical test strip and, based upon the detection, operate the analyte measurement circuit to apply a testing waveform across the fluid sample and measure a resulting electrochemical response. 
     
     
         5 . The system according to  claim 4 , wherein the reagent is configured in the sample chamber such that the electrochemical response represents a glucose level in the fluid sample. 
     
     
         6 . The system according to  claim 4 , wherein the testing waveform includes an alternating-current waveform. 
     
     
         7 . The system according to  claim 3 , wherein the detection electrodes are laterally adjacent to each other and are arranged on the opposite side of the sample chamber from the sample electrode. 
     
     
         8 . The system according to  claim 1 , wherein the impedance-measurement circuit includes a voltage supply configured to apply the alternating-current waveform and a transimpedance amplifier configured to detect a current through the reagent while the alternating-current waveform is applied. 
     
     
         9 . The system according to  claim 1 , wherein the test meter includes two presence-detect contacts configured to electrically contact a selected one of the detection electrodes of the received analytical test strip and a presence-detection circuit configured to detect electrical continuity between the two presence-detect contacts, and the processor is further configured to automatically cause application of the alternating-current waveform subsequent to detection of the electrical continuity. 
     
     
         10 . The system according to  claim 9 , wherein the test meter further includes a switch for selectively electrically isolating at least one of the two presence-detect contacts from the received analytical test strip when open, and the processor is further configured to automatically cause opening of the switch after the impedance of the reagent is measured. 
     
     
         11 . The system according to  claim 1 , wherein the selected dryness criterion is an impedance of about 0Ω to about 1 MΩ and the impedance-measurement circuit is configured to apply the alternating-current waveform at a frequency of about 10 kHz. 
     
     
         12 . A hand-held test meter for use with an analytical test strip, the test meter comprising:
 a) a housing;   b) a strip port connector configured to receive the analytical test strip and to electrically connect to two spaced-apart detection electrodes of the received analytical test strip;   c) an impedance-measurement circuit arranged in the housing and configured to apply an alternating-current waveform across a reagent in a sample chamber of the received analytical test strip via the strip port connector, and to concurrently measure an impedance of the reagent; and   d) a processor configured to automatically determine whether the measured impedance of the reagent meets a selected dryness criterion.   
     
     
         13 . The meter according to  claim 12 , wherein the strip port connector is further configured to electrically connect to a sample electrode of the received analytical test strip and the meter further includes an analyte measurement circuit electrically connected to the sample electrode and at least one of the spaced-apart detection electrodes. 
     
     
         14 . The meter according to  claim 13 , wherein the processor is further configured to, if the measured impedance of the reagent meets the dryness criterion, detect the presence of the fluid sample in the sample chamber of the received analytical test strip and, based upon the detection, operate the analyte measurement circuit to apply a testing waveform across the fluid sample and measure an electrochemical response to the testing waveform. 
     
     
         15 . The meter according to  claim 14 , wherein the reagent is configured so that the electrochemical response represents a glucose level in the fluid sample. 
     
     
         16 . The meter according to  claim 12 , further including a user interface, wherein the processor is configured to, if the measured impedance does not meet the selected dryness criterion, present an error indication via the user interface. 
     
     
         17 . A method for determining usability of an analytical test strip inserted in a hand-held test meter, the method comprising performing the following steps using a processor and at least one electrical circuit of the test meter:
 applying an alternating-current waveform across a reagent of the inserted analytical test strip and measuring a first electrical signal; and   determining whether the inserted analytical test strip meets a selected dryness criterion based on the first electrical signal.   
     
     
         18 . The method according to  claim 17 , further including, if the inserted analytical test strip meets the selected dryness criterion:
 detecting a fluid sample in a sample chamber of the inserted analytical test strip;   applying a voltage signal across the detected fluid sample in the sample chamber and measuring a second electrical signal mediated by the reagent; and   determining a physiological property of the fluid sample using the second electrical signal.   
     
     
         19 . The method according to  claim 18 , wherein the reagent is configured so that the second electrical signal represents a blood glucose level in the fluid sample. 
     
     
         20 . The method according to  claim 17 , further including, if the measured impedance does not meet the selected dryness criterion, automatically presenting an error indication via a user interface. 
     
     
         21 . An electrochemical-based analytical test strip comprising:
 a) an electrically-insulating bottom layer;   b) a patterned electrically-conductive layer disposed on the electrically insulating bottom layer that includes a first patterned portion and a second patterned portion;   c) an enzymatic reagent layer disposed on the first patterned portion, the second patterned portion and the electrically-insulating bottom layer such that the enzymatic reagent layer bridges the first patterned portion and the second patterned portion;   d) a patterned spacer layer;   e) a top electrically conductive layer; and   f) an electrically-insulating top layer.   
     
     
         22 . A method for the determination of an analyte in a bodily-fluid sample, the method comprising:
 ascertaining whether an enzymatic reagent layer of an electrochemical-based analytical test strip has been exposed to a predetermined humidity level by measuring an electrical characteristic of the enzymatic reagent layer, the electrochemical-based analytical test strip having:
 an electrically-insulating bottom layer; 
 a patterned electrically-conductive layer disposed on the electrically insulating bottom layer and including a first patterned portion and a second patterned portion; 
 an enzymatic reagent layer disposed on the first patterned portion, the second patterned portion and the electrically-insulating bottom layer such that the enzymatic reagent layer bridges the first patterned portion and the second patterned portion; 
 a patterned spacer layer; 
 a top electrically conductive layer; and 
 an electrically-insulating top layer; 
   applying the bodily-fluid sample to the electrochemical-based analytical test strip; and   determining the analyte based on an electrochemical response of the electrochemical-based analytical test strip.