Human Exhalation CO₂ Sensor Based on the PEI-PEG/ZnO/NUNCD/Si Heterojunction Electrode

Area of Science:

• Materials Science
• Chemical Engineering
• Biomedical Engineering

Background:

• Semiconductor gas sensors offer high sensitivity but suffer from high operating temperatures, limiting practical applications.
• Chronic Obstructive Pulmonary Disease (COPD) diagnosis currently relies on invasive arterial blood sampling, causing patient discomfort and reducing willingness to undergo testing.
• Noninvasive monitoring of carbon dioxide (CO2) levels is essential for early detection and management of high-risk COPD patients.

Purpose of the Study:

• To develop a highly sensitive and selective semiconductor CO2 sensor for noninvasive COPD diagnosis.
• To improve the performance of existing CO2 sensors by incorporating novel materials.
• To investigate the sensing mechanisms and material contributions to sensor performance.

Main Methods:

• Fabrication of a composite film by incorporating nitrogen-incorporated ultrananocrystalline diamond (NUNCD) into a polyetherimide-polyethylene glycol (PEI-PEG) polymer.
• Integration of the composite film with a ZnO/NUNCD/Si electrode to create a novel gas sensor.
• Analysis of experimental results using theoretical regression to understand the sensor's performance.

Main Results:

• The developed PEI-PEG/ZnO/NUNCD/Si electrode exhibited excellent performance as a CO2 sensor.
• The sensor's performance was attributed to two main reaction layers: the PEI-PEG adsorption layer and the ZnO/NUNCD electric transfer layer.
• High aspect ratio, flower-like ZnO structures significantly enhanced the sensor's sensitivity by providing a larger active adsorption area.

Conclusions:

• The novel composite material significantly improves CO2 sensor sensitivity and selectivity.
• The sensor design offers a promising noninvasive approach for early COPD diagnosis.
• Understanding the roles of adsorption and electric transfer layers provides insights for future sensor development.