Title: Mid-IR refractive index sensor for detecting proteins employing an external cavity quantum cascade laser-based Mach-Zehnder interferometer
Authors: Dabrowska, Alicja 
Schwaighofer, Andreas  
Lindner, Stefan 
Lendl, Bernhard  
Category: Original Research Article
Issue Date: 23-Nov-2020
Journal: Optics Express 
ISSN: 1094-4087
Novel laser light sources in the mid-infrared region enable new spectroscopy schemes beyond classical absorption spectroscopy. Herein, we introduce a refractive index sensor based on a Mach-Zehnder interferometer and an external-cavity quantum cascade laser that allows rapid acquisition of high-resolution spectra of liquid-phase samples, sensitive to relative refractive index changes down to 10−7. Dispersion spectra of three model proteins in deuterated solution were recorded at concentrations as low as 0.25 mg mL−1. Comparison with Kramers-Kronig-transformed Fourier transform infrared absorbance spectra revealed high conformance, and obtained figures of merit compare well with conventional high-end FTIR spectroscopy. Finally, we performed partial least squares-based multivariate analysis of a complex ternary protein mixture to showcase the potential of dispersion spectroscopy utilizing the developed sensor to tackle complex analytical problems. The results indicate that laser-based dispersion sensing can be successfully used for qualitative and quantitative analysis of proteins.
Keywords: Mid-infrared spectroscopy; dispersion spectroscopy; Mach-Zehnder interferometer; quantum cascade laser; refractive index sensing; protein analysis
DOI: 10.1364/OE.403981
Organisation: E164-02-1 - Forschungsgruppe Prozessanalytik 
License: CC BY 4.0 CC BY 4.0
Publication Type: Article
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