How blood glucose test strips work

How blood glucose test strips work

How it works: sensors and current analysis

The first step to measuring glucose in the blood is to convert it to a glucose or voltage signal with a glucose concentration, which is possible with amperometric methods with special sensor bands. The sensor uses a platinum and silver electrode to form part of a circuit in which hydrogen peroxide is electrolyzed.

As a result, the oxidation of the glucose oxide film on glucose produces hydrogen peroxide. The current flowing in the circuit provides a measured hydrogen peroxide concentration, giving the glucose concentration.

It is important to emphasize that the relationship expressed in the equation (Figure 1 below) is linear. This is different in reality because it may be involved in reactions as well as other biochemical substances.

figure 1. Electrode reaction

The sensor used as a blood glucose meter is based on a glucose oxide electrode. A glucose oxide to which a platinum-plated activated carbon electrode is fixed. Enzyme electrode for amperometric determination of hydrogen peroxide produced by enzymes that use electrochemical detection.

The sensors consist of various electrodes: a thin film of glucose oxide, a polyurethane membrane permeable to glucose, oxygen and hydrogen peroxide.

Electrolytic reactions between counter-electrodes driven by currents measured by galvanometry. Oxygen diffuses through the membrane and a voltage is applied to the Pt electrode to reduce it to H 2 O 2.

figure 2. Basic test block diagram

These reactive electrode amperometric sensors use a three-electrode design. This method is useful when using electrochemical sensors due to the reliability of measuring voltage and current in the same chemical reaction.

The three electrode model uses a working electrode (WE), a reference electrode (RE), and a counter electrode (CE). After the current is generated, it must be changed to a voltage and processed by a microcontroller (MCU). This action is performed by a transimpedance amplifier. Finally, the MCU detects and processes this signal with the ADC module.

For example, here is a practical way to explain amps. A voltage is applied in the range of -200 milivots to 8 volts for the WE and RE electrodes. This is used to define the voltage at which the sensor is capable of performing at maximum current.

This value is a voltage of approximately 4 volts and a current of 18 microamperes. After selecting a voltage of 4 volts as the operating value, we obtain a stabilization time between 2 and 4 seconds. This means that reliable measurements can be obtained during this time, as the maximum current is reached.