Determining blood glucose in a small volume sample receiving cavity and in a short time period
View Patent ↗The concentration of glucose in a blood sample is determined by methods utilizing test strips having a sample receiving cavity having a volume from about 0.3 μl to less than 1 μl and determining the glucose concentration within a time period from about 3.5 seconds to about 8 seconds.
1. A method of analyzing an analyte in a biological fluid sample, the method comprising:
providing an electrochemical sensor comprising:
a flexible substrate;
a conductive pattern disposed on the flexible substrate, the conductive pattern comprising:
an interdigitated array comprising first and second, electrodes electrically isolated from each other, the first electrode comprising first electrode elements electrically connected to a first common element, the second electrode comprising second electrode elements electrically connected to a second common element the number of first electrode elements being one more or one less than the number of second electrode elements;
first and second pads and first and second connectors electrically connecting the first and second pads to the first and second electrodes, respectively;
wherein each electrode element comprises a width of about 50 micrometers, and wherein the electrode elements of the first electrode are spaced substantially equally from the electrode elements of the second electrode by gaps, each gap having, a distance of about 25 micrometers;
a chemical coating disposed over at least a portion of the first electrode, the chemical coating configured for reacting with an analyte to produce an electroactive reaction product; and
a capillary chamber overlying at least a portion of the interdigitated array and configured to direct flow of a biological fluid sample into contact with the chemical coating on the first electrode, the capillary chamber having a volume from about 250 nanoliters to about 400 nanoliters;
contacting the capillary chamber with a biological fluid sample, the capillary chamber directing the biological fluid sample into contact with the first and second electrodes and the chemical coating to at least partly solubilize or hydrate the chemical coating;
detecting the contacting of the first and second electrodes by the biological fluid sample and starting a delay period of about 2 seconds allowing the analyte and chemical coating to react and to produce electroactive reaction product;
after the delay period, starting an assay period by applying an assay potential across the first and second electrodes for inducing an assay current across the electrodes resulting from oxidation of the electroactive reaction product at one of the first and second electrodes, the assay current reaching a steady-state current;
measuring a magnitude of the assay current during the assay period after the assay current has reached the steady-state current, the measuring step being performed beginning about 2.1 seconds after the start of the delay period; and
correlating the magnitude of the assay current to a concentration of the analyte in the biological fluid sample.
2. The method of claim 1 , wherein the biological fluid sample comprises whole blood, and the analyte comprises glucose.
3. The method of claim 1 , wherein the measuring step is performed at a fixed assay period point during the assay period, and wherein the magnitude of the assay current at the fixed assay period point correlates generally linearly with the concentration, of the analyte over a range of concentrations.
4. The method of claim 3 , wherein the biological fluid sample comprises whole blood, the analyte comprises glucose, and the concentration range comprises from about 0 to about 600 mg/dL.