Quantum cascade lasers (QCLs) in biomedical spectroscopy

Abstract

Quantum cascade lasers (QCL) are the first room temperature semiconductor laser source for the mid-IR spectral region, triggering substantial development for the advancement of mid-IR spectroscopy. Mid-IR spectroscopy in general provides rapid, label-free and objective analysis, particularly important in the field of biomedical analysis. Due to their unique properties, QCLs offer new possibilities for development of analytical methods to enable quantification of clinically relevant concentration levels and to support medical diagnostics. Compared to FTIR spectroscopy, novel and elaborated measurement techniques can be implemented that allow miniaturized and portable instrumentation. This review illustrates the characteristics of QCLs with a particular focus on their benefits for biomedical analysis. Recent applications of QCL-based spectroscopy for analysis of a variety of clinically relevant samples including breath, urine, blood, interstitial fluid, and biopsy samples are summarized. Further potential for technical advancements is discussed in combination with future prospects for employment of QCL-based devices in routine and point-of-care diagnostics.

A quantum cascade laser-based Mach–Zehnder interferometer for chemical sensing employing molecular absorption and dispersion

“…Assuming no additional noise sources for the interferometric phase, LODs for the refractive index can be estimated based on the noise floor of the signal since this signal's minimum with respect to φ defines the refractive index (see (2)). An estimate of LODs equivalent to (15) using the sensitivity dP sig,int /dφ is prohibited by the vanishing sensitivity at φ = 0.…”

“…More recently, quantum cascade lasers (QCL) were employed successfully to replace notoriously weak thermal emitters as Mid-IR sources. In particular, external cavity (EC) QCLs proved to be an ideal match for many liquid sensing applications owing to their large spectral tuning range of typically 200 cm −1 [1][2][3][4][5][6][7][8][9]. To date, the vast majority of measurements are performed using direct absorption spectroscopy, in which the laser beam's intensity is recorded after passing through the sample or being totally reflected at its surface.…”

Application of a Novel Low-Cost Hyperspectral Imaging Setup Operating in the Mid-Infrared Region

“…This indicates the importance of the optical design and the sample illumination. Depending on the specific demands of the application, the illumination can also be executed by newly available MIR laser-based light sources such as quantum cascade lasers [5] or supercontinuum lasers [6]. For the first time hyperspectral imaging in the decisive fingerprint region was realized to be low-cost and small-sized.…”

High-throughput quantitation of bovine milk proteins and discrimination of commercial milk types by external cavity-quantum cascade laser spectroscopy and chemometrics

“…Consequently, custom-built setups for IR spectroscopy based on quantum cascade lasers were developed to overcome the disadvantages of FTIR instruments, and already diverse applications in mid-IR spectroscopy were reported. 25 In IR transmission spectroscopy of proteins, the transmission paths could be considerably increased by using an external cavity-quantum cascade laser (EC-QCL) light source that provides significantly higher emission powers. 26 Laser-based IR transmission measurements were successfully performed for examination of the protein secondary structure by evaluation of the amide I band.…”