Design of blood analyzer

Recent innovations in blood analyzers have made it easier than ever to quickly measure blood, such as blood gases, glucose, electrolytes, coagulation, chemistry, hematology, and cardiac markers (cTnI). At the same time, with the emergence of new digital technology, invasive blood analyzers will become portable and used to measure the two major metabolic disorders in the blood system: glucose and cholesterol.

The two main methods used to measure blood are color reflectance and electromechanical sensor technology (amperometric method).

The analog front end of the reflectometry method generally uses an optical sensor (LED, phototransistor) and a transimpedance amplifier. Measurements using the color reflectometry method are based on the intensity of the color reflected by the reflective layer of the test strip, which is achieved through reflectance photometry. The analyzer quantifies the color change and generates a digital value to represent the cholesterol/glucose concentration in the blood.

In the amperometric method, the biosensor (test strip) is directly connected to a transimpedance amplifier. The cholesterol/glucose present in the blood reacts chemically with the test strip and changes in the test strip, which is measured by the amperometric method. For the amperometric method, it is particularly important to pay attention to the determination of the ambient temperature in order to compensate for the characteristics of the test strip.

The measurement sequence is usually controlled by a microcontroller (MCU). The microcontroller also processes the conversion results, stores the measurement results in EEPROM or flash memory and controls other functions such as the keyboard area, real-time clock, sound/voice compression and serial communication to connect to a PC.

The audio output is provided by a PWM circuit or a DAC. Both methods can generate a "beep" indication signal when the measurement result is obtained and generate a voice command through the adopted speech synthesizer software (such as ADPCM compression algorithm). The measurement result will be stored in the form of a data log in EEPROM or flash memory together with the measurement time and data. The data log can also be uploaded to a PC through the RS-232 or USB interface.