High-sensitivity CO2 sensing via quartz-enhanced photoacoustic spectroscopy enabled by a custom-grooved quartz tuning fork

Quartz-enhanced photoacoustic spectroscopy (QEPAS) relies on the quartz tuning fork (QTF) as the core acoustic-electrical transducer, whose properties critically affect detection sensitivity. In this work, a customgrooved QTF with large prong spacing and low resonance frequency was designed and fabricated to effectively suppress background noise, improve the matching between molecular relaxation and acoustic resonance, and enhance piezoelectric signal collection efficiency, thereby improving detection performance. Meanwhile, an erbium-doped fiber amplifier (EDFA) was employed to construct a high-power excitation QEPAS system. Benefiting from the combined optimization of the QTF structure and excitation power, the proposed system achieved an enhancement of nearly 3 orders of magnitude in detection performance compared with a standard QTF, with a minimum detection limit (MDL) of 0.9 ppm for CO2. To further demonstrate its practical applicability, the proposed system was evaluated in three representative scenarios, namely ambient air monitoring, human breath analysis, and dissolved gas analysis in transformer oil. The results demonstrate reliable tracking of atmospheric and respiratory CO2 variations, as well as sensitive detection of dissolved CO2 in transformer oil. Overall, the proposed QEPAS system exhibits high sensitivity, good stability, and strong adaptability, demonstrating promising potential for practical gas sensing applications.