Cavity ringdown spectroscopic detection of nitric oxide with a continuous-wave quantum-cascade laser

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Gas Sensing Technology

Background:

• Nitric oxide (NO) is a crucial biomarker in various physiological and pathological processes.
• Accurate and sensitive detection of NO is essential for medical diagnostics and environmental monitoring.
• Existing NO detection methods may lack the required sensitivity or real-time capabilities for certain applications.

Purpose of the Study:

• To design and evaluate a novel spectroscopic gas sensor for highly sensitive nitric oxide (NO) detection.
• To demonstrate the feasibility of using a cavity ringdown technique for NO quantification.
• To assess the sensor's performance for potential application in analyzing NO in human breath.

Main Methods:

• Utilized a continuous-wave (cw) quantum-cascade distributed-feedback laser operating at 5.2 µm as a tunable single-frequency light source.
• Employed cavity ringdown spectroscopy (CRDS) for high-sensitivity absorption measurements.
• Manipulated laser current for precise laser-frequency tuning and controlled interruption of laser radiation.

Main Results:

• Achieved a single ringdown event sensitivity to absorption of 2.2 x 10⁻⁸ cm⁻¹.
• Successfully measured nitric oxide (NO) concentrations in nitrogen (N₂) at parts per billion (ppb) levels.
• Obtained a standard error of 0.7 ppb for NO measurements with a data collection time of 8 seconds.

Conclusions:

• The developed spectroscopic gas sensor demonstrates high sensitivity and accuracy for NO detection.
• The cavity ringdown technique is effective for ppb-level NO quantification.
• Future improvements could enable in-vivo NO quantification in human breath, aiding in medical diagnostics.