Figure 2. Electrode reactions between glucose and gluconic acid

The sensor used as a blood-glucose meter is based on a glucose oxide electrode. The glucose oxides were immobilized in a

platinized activated carbon electrode. The enzyme electrode was used for amperometry determination by using an electrochemical

detection of enzymically produced hydrogen peroxide. The sensor is composed of various electrodes; a glucose oxide membrane

layer, a polyurethane film that is permeable by the glucose, oxygen, and hydrogen peroxide.

2.3 Amperometry

Amperometry measures electric current between a pair of electrodes that are driving the electrolysis reaction. Oxygen diffuses

Figure 3. Test strip basic block diagram

These reactive electrodes are amperometric type sensors that use a three electrode design. This approach is useful when using

amperometric sensors due to the reliability of measuring voltage and current in the same chemical reaction. Three electrode

models use a working electrode (WE), reference electrode (RE), and a counter electrode (CE). After this current is produced

this must be changed to voltage for processing by the MCU. This action is performed by the transimpedance amplifier. Finally,

the MCU detects and processes this signal with the ADC module. For a transimpedance amplifier and sensor designs for medical

applications go to Medical Application User Guide at www.freescale.com.

Implementing a Glucometer and Blood Pressure Monitor Medical Devices, Rev. 1, 4/2010

3

Freescale Semiconductor, Inc.

Glucometers and Diabetes