Systems and methods for blood glucose sensing

A test strip for testing a blood sample, said test strip comprising:

• a sample chamber for said blood sample;
• at least four electrodes for measuring at least one electrical characteristic of said blood sample in said sample chamber, said at least four electrodes including a working electrode, a counter electrode, a fill-detect anode, and a fill-detect cathode;
• a plurality of electrical contacts electrically connected to said at least four electrodes;
• and
• at least one auto-on electrical contact electrically isolated from said at least four electrodes.

A method of making a plurality of test strips, said method comprising:

• forming a plurality of test strip structures on a first insulating sheet, wherein each test strip structure is formed by:
• (a) forming a first conductive pattern on said first insulating sheet, said first conductive pattern including at least four electrodes, said at least four electrodes including a working electrode, a counter electrode, a fill-detect anode, and a fill-detect cathode;
• (b) forming a second conductive pattern on said first insulating sheet, said second conductive pattern including a plurality of electrode contacts for said at least four electrodes, a plurality of conductive traces electrically connecting said at least four electrodes to said plurality of electrode contacts, and an auto-on conductor;
• (c) applying a first dielectric layer over portions of said working electrode and said counter electrode, so as to define an exposed working electrode portion and an exposed counter electrode portion;
• (d) applying a second dielectric layer to said first dielectric layer, said second dielectric layer defining a slot, said working electrode, said counter electrode, said fill-detect anode, and said fill-detect cathode being disposed in said slot;
• (e) forming a reagent layer in said slot, said reagent layer including glucose oxidase and a mediator;
• (f) forming an adhesive layer on said second dielectric layer, said adhesive layer having a break extending from said slot;
• and
• (g) attaching a second insulating layer to said adhesive layer, such that said second insulating sheet covers said slot but not said electrode contacts or said auto-on conductor;
• and
• separating said plurality of test strip structures into said plurality of test strips, each of said test strips having a proximal end and a distal end, with said slot extending to said proximal end, said proximal end being narrower than said distal end.

A method of making a plurality of test strips, said method comprising:

• forming a plurality of test strip structures on one sheet, each of said test strip structures including:
• (a) a sample chamber;
• (b) a plurality of electrodes, including a working electrode, a counter electrode, a fill-detect anode, and a fill-detect cathode;
• (c) a plurality of electrical contacts electrically connected to said plurality of electrodes;
• and
• (d) at least one auto-on electrical contact, electrically isolated from said plurality of electrodes;
• and
• separating said test strip structures into said plurality of test strips.

A method of measuring glucose in a blood sample, said method comprising:

• providing a test strip, said test strip having a sample chamber, with a working electrode, a counter electrode, a pair of fill-detect electrodes, and a reagent layer disposed in said sample chamber, said reagent layer including glucose oxidase and a mediator, said test strip including an auto-on conductor;
• inserting said test strip into a meter, said meter being in a sleep mode;
• said meter detecting an auto-on current through said auto-on conductor and responsively entering an active mode;
• said meter validating said working and counter electrodes by applying a first validation voltage between said working and counter electrodes;
• said meter validating said fill-detect electrodes by applying a second validation voltage between said fill-detect electrodes, while said first validation voltage is applied between said working and counter electrodes;
• applying said blood sample to said sample chamber;
• said meter detecting said blood sample at a first location in said sample chamber by applying a drop-detect voltage between said working and counter electrodes and measuring a drop-detect current flowing between said working and counter electrodes;
• said meter detecting said blood sample at a second location in said sample chamber by applying a fill-detect voltage between said fill-detect electrodes and measuring a fill-detect current flowing between said fill-detect electrodes;
• after waiting an incubation time period, said meter applying an assay voltage between said working and counter electrodes and making at least one measurement of the resulting current through said working electrode;
• and
• said meter determining a measured glucose level from said at least one current measurement.

A method of using a test strip to test a blood sample, said test strip including a sample chamber, a working electrode, a counter electrode, a pair of fill-detect electrodes, and an auto-on conductor, said method comprising:

• inserting said test strip into a meter, said meter being in a sleep mode;
• said meter detecting an auto-on current through said auto-on conductor and responsively entering an active mode;
• applying said blood sample to said sample chamber;
• said meter detecting said blood sample in said sample chamber by applying a fill-detect voltage between said fill-detect electrodes and measuring a fill-detect current flowing between said fill-detect electrodes;
• said meter applying an assay voltage between said working and counter electrodes and making at least one measurement of the resulting current;
• and
• said meter determining a test result from said at least one current measurement.

A method of strip identification, said method comprising:

• inserting a strip into a meter, said strip including an auto-on conductor, said meter being in a sleep mode;
• said meter detecting said strip, by detecting a current flow through said auto-on conductor, and responsively entering an active mode;
• said meter measuring a voltage drop across said auto-on conductor;
• said meter identifying said strip as either a test strip or a check strip based on said voltage drop;
• if said strip is a test strip, said meter performing a test strip sequence;
• and
• if said strip is a check strip, said meter performing a check strip sequence.

A removable data storage device for a meter, said meter measuring using test strips to measure glucose levels in blood samples, said removable data storage device comprising:

• a carrier having a proximal end and a distal end, said carrier being keyed for inserting said distal end into said meter in a preferred orientation;
• a circuit board mounted to said carrier, said circuit board including a plurality of electrical contacts for electrically connecting to said meter, said plurality of electrical contacts including a ground contact and a voltage supply contact, said ground contact extending closer to said distal end than said voltage supply contact;
• and
• a memory mounted to said circuit board and electrically connected to said plurality of electrical contacts, said memory storing data for use by said meter, said data including at least one calibration parameter for use with at least one test strip,
• whereby when said removable data storage device is inserted into said meter in said preferred orientation, said ground contact becomes electrically connected to said meter before said voltage supply contact.

A meter for use in combination with a test strip for measuring a glucose level in a blood sample applied to a sample chamber in said test strip, said test strip having at least four electrodes disposed in said sample chamber, said at least four electrodes including a working electrode, a counter electrode, and a pair of fill-detect electrodes, said test strip having a thin section and a thick section, said thin section including a plurality of test strip contacts for said at least four electrodes and an auto-on conductor, said meter comprising:

• a first connector for receiving said test strip, said first connector including meter contacts for electrically connecting to said test strip contacts and said auto-on conductor, said first connector being sized to receive said thin section but not said thick section of said test strip;
• a second connector for receiving a removable data storage device, said removable data storage device storing data for use by said meter;
• a processor;
• a memory;
• a display;
• a plurality of machine language instructions stored in said memory and executable by said processor for:
• a) saving said data from said removable data storage device into said memory;
• b) performing a test strip sequence when said test strip is inserted in said first connector to obtain at least one current measurement related to said glucose level;
• c) determining a glucose level in said blood sample from said at least one current measurement and said data stored in said memory;
• and
• d) displaying said glucose level on said display;
• a first electrode circuit for applying at least a first voltage, selected by said processor, between said working and counter electrodes when said test strip is inserted in said first connector, said first electrode circuit including a first digital-to-analog converter;
• a second electrode circuit for applying at least a second voltage, selected by said processor, between said fill-detect electrodes when said test strip is inserted in said first connector, said second electrode circuit including a second digital-to-analog converter;
• an auto-on circuit for developing an auto-on current through said auto-on conductor when said test strip is inserted in said first connector and for bringing said meter from a sleep mode to an active mode in response to said auto-on current;
• and
• at least one analog-to-digital converter for measuring currents flowing between said working and counter electrodes and flowing between said fill-detect electrodes and for measuring an auto-on voltage drop across said auto-on conductor resulting from said auto-on current.

A meter for use in combination with a test strip, said test strip including a working electrode, a counter electrode, a pair of fill-detect electrodes, and an auto-on conductor, said meter comprising:

• a strip connector for receiving said test strip;
• a processor;
• a memory;
• a plurality of machine instructions stored in said memory and executable by said processor for performing a test strip sequence;
• a data acquisition system, controlled by said processor, for applying at least a first voltage between said working and counter electrodes and measuring any resulting current flowing between said working and counter electrodes, for applying at least a second voltage between said fill-detect electrodes and measuring any resulting current flowing between said fill-detect electrodes, and for measuring a voltage drop across auto-on conductor, when said test strip is inserted in said strip connector, said data acquisition system including at least one digital-to-analog converter and at least one analog-to-digital converter.