Broadband laser-based mid-infrared spectroscopy employing a quantum cascade detector for milk protein analysis

Mid-infrared chemical sensors based on quantum cascade technology offer a number of properties surpassing conventional spectrometric techniques. In this work, we combine a tunable quantum cascade laser with a spectrally tailored in-house fabricated quantum cascade detector (QCD) to realize broadband detection of aqueous samples for selective sensing of bovine milk proteins. The developed setup enables broadband spectroscopy covering more than 260 cm-1 and was employed to record absorbance spectra of the amide I and amide II bands of beta-lactoglobulin, alpha-lactalbumin and casein. A detailed comparison indicates similar performance of the laser-based setup with its uncooled QCD as a high-end FTIR spectrometer equipped with a liquid nitrogen cooled mercury-cadmium-telluride (MCT) detector. Furthermore, we discuss the characteristics and benefits of the quantum cascade detector for application in laser-based mid-infrared sensor systems and compare its performance to other common mid-infrared detector types. In conclusion, the combination of QCDs with EC-QCLs opens up new possibilities for next-generation MIR liquid-phase chemical sensors featuring low noise and high dynamic range.