Abstract
Optical methods based on quantum cascade lasers (QCLs) are becoming popular in many life science ap- plications. We report on two trace gas detection schemes based on continuous wave QCLs for on-line detection of nitric oxide (NO) at the sub-part-per-billion level by vol- ume (ppbv, 1 : 10 −9 ), using wavelength modulation spec- troscopy (WMS) and Faraday rotation spectroscopy (FRS) at 1894 cm −1 and 1875.73 cm −1 , respectively. Several tech- nical incremental steps are discussed to further improve the sensitivity of these methods. Examples are included to demonstrate the merits of WMS-based sensor: direct mon- itoring of NO concentrations in exhaled breath, and from plants under pathogen attack. A simple hand-held breath sampling device that allows single breath collection at var- ious exhalation flows (15, 50, 100 and 300 mL/s, respec- tively) is developed for off-line measurements and validated in combination with the WMS-based sensor. Additionally, the capability of plants to remove environmental NO is pre-
Highlights
In 1890 Alfred Nobel’s physicians prescribed nitroglycerine as a remedy for his heart disease
quantum cascade lasers (QCLs) emitting in the nitric oxide (NO) fundamental vibration-rotation band have in recent years triggered the development of QCL-based NO sensors using various spectroscopic methods including direct absorption spectroscopy using multi-pass cells [12], wavelength modulation spectroscopy [13], photoacoustic spectroscopy [14], Faraday rotation spectroscopy (FRS) [15] and high-finesse cavities for extreme absorption path length, i.e. cavity ring-down spectroscopy and on/off-axis integrated cavity output spectroscopy [16, 17]
wavelength modulation spectroscopy (WMS) on a QCL emitting in the strongest absorption region of NO and coupled with a multi-pass cell has led to the development of a simple, robust and sensitive sensor suitable for detection of NO in multiple applications
Summary
In 1890 Alfred Nobel’s physicians prescribed nitroglycerine (a key component of dynamite) as a remedy for his heart disease. The quantum cascade laser (QCL) technology has rapidly advanced during the last years, offering narrow linewidth, high power at room temperature and continuous wave (cw) operation at mid-IR wavelengths (3–24 μm) [5, 6] These features are nowadays combined with a wide collection of non-invasive optical methods for selective, sensitive and accurate analysis of NO concentrations [6,7,8,9]. Several medical reports have shown their high performances in terms of sensitivity, selectivity and accuracy in comparison to other technologies [10] Another great advantage offered by optical sensors is the possibility to perform multiple flow rate analysis (exhaled NO concentration is flow dependent) without modification of the sensor [4]. The suitability of WMS-based sensors for accurate detection of NO in planta is shown in two important plant research areas, pathogen infection and NO removal from the atmosphere
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