A MEMS Microbolometer-Based ATR Mid-Infrared Sensor for Direct Dissolved CO2 Detection and UV-Induced Sediment Carbon Assay in Aquatic Environments

Monitoring dissolved carbon dioxide (CO2) in aquatic and sediment systems is critical for understanding carbon cycling and climate feedback. This study develops and characterizes a compact, low-cost microbolometer-based attenuated total reflectance (ATR) mid-infrared sensor for direct dissolved CO2 measurement in liquid and soil-water environments. The system integrates a ZnSe ATR crystal with custom suspended SiN membrane microbolometers and uses evanescent-wave absorption at 4.26 μm with a broadband LED source and computational spectral reconstruction, eliminating the need for an interferometer. Calibration shows excellent linearity (R2 ≈ 0.99) over 50–1000 ppm CO2, with a practical limit of detection (LOD) of ~26–35 ppm at 5–25 °C. UV-induced CO2 generation from soil-water mixtures was investigated across UV wavelengths, revealing UV-C (254 nm) as optimal, producing net ΔCO2 ≈ 339 ppm above ambient levels in 30 min. Environmental factors (temperature 5–35 °C, pH 5–11, pressure 1–1.5 ATM, dissolved organic carbon) were systematically evaluated, confirming robust sensor performance (accuracy >90%, correlation r > 0.98 with reference instrument). This sensor represents the first integration of MEMS microbolometer detectors with ATR evanescent-wave spectroscopy for liquid-phase dissolved CO2, enabling real-time monitoring and rapid sediment organic carbon assessment in a field-deployable platform.