QCL-IR Absorption Spectroscopy of Proteins


Mid-infrared spectroscopy is a well-established technique for the analysis of polypeptides and proteins. The amide I band (1700-1600 cm-1) originating from C=O stretching coupled to in-phase bending vibration of N-H and the amide II band (1600-1500 cm-1) arising from N-H bending and C-N stretching vibrations are the most useful bands for secondary structure evaluation and quantification of proteins.
Strong absorption of H2O near 1640 cm-1 makes IR studies of proteins in aqueous solutions challenging. For conventional Fourier-transform infrared spectroscopy, very short pathlength of approx. 10 µm are needed to avoid total IR absorption in the spectral region of water. These low path lengths limit the intensities of the IR bands and the signal-to-noise ratio, thus restricting the application to high protein concentrations (approx. 10 mg/mL).
EC-QCLs, which provide spectral power densities several orders of magnitude higher than thermal emitters,  allow the use of 4-5 times higher path length and consequently the detection of proteins at lower concentrations.


Development of Laser-based IR Transmission Setups for Analysis of Proteins

In the last few years, several iterations of EC-QCL based IR transmission setups were developed to analyse the amide I and amide II regions of proteins. The latest iteration provides an improved limit of detection compared to research grade FT-IR instruments at spectra acquisition times lower than 1 min.  

Key Publications:

Book Chapter:


Inline Monitoring of Proteins from Preparative Liquid Chromatography

A commercial EC-QCL based IR Instrument (Chemdetect Analyzer by Daylight Solutions) was employed for inline monitoring of proteins from preparative ion-exchange chromatography (IEX) and size exclusion spectroscopy (SEC).