Glucose Sensors
Three glucose sensors were developed based on different technology platforms:
• a classical amperometric sensor using thick film technology;
• a fibre-optic fluorometric glucose sensor based on oxygen measurement, and
• a spectroscopic glucose sensor using mid-infrared spectroscopy
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http://www.geeky-gadgets.com/glucowizzard-implant-sensors-monitors-blood-glucose-levels-03-03-2010/
http://www.solaramedicalsupplies.com/Medtronic-cgm-sensors
The sensor uses a platinum and silver electrode to form part of an electric circuit where hydrogen peroxide is electrolysed. The hydrogen peroxide is produced as a result of the oxidation of glucose on a glucose oxide membrane. The current flowing through the circuit provides a measurement of the concentration of hydrogen peroxide, giving the glucose concentration.
The sensor used as a blood glucose meter is based on a glucose oxide electrode. The glucose oxides are immobilised in a platinised activated carbon electrode. The enzyme electrode is 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.
Amperometry measures electric current between a pair of electrodes that are driving the electrolysis reaction. Oxygen diffuses through the membrane and a voltage is applied to the Pt electrode reducing O2 to H2.
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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, it must be changed to voltage for processing by the microcontroller (MCU). This action is performed by the transimpedance amplifier. Finally, the MCU detects and processes this signal with the ADC module.
For example, here is a practical way to explain amperometry. A voltage is applied in the WE and RE electrodes with a range of -200 milivots to 8 volts. This is used to define the voltage at which the sensor is able to perform at the maximum current. This value is around 4 volts with a current of 18 microamperes After selecting the 4 volts as an operating value, we obtain a stabilization time between 2 and 4 seconds. This means a reliable measurement can be obtained in this time since the maximum current is reached.
http://www.electronicsweekly.com/ne.../analysis-blood-glucose-meter-design-2011-05/
Best regards,
Peter
;-)