Single-Shot Sub-microsecond Mid-infrared Spectroscopy on Protein Reactions with Quantum Cascade Laser Frequency Combs

Abstract

The kinetic analysis of irreversible protein reactions requires an analytical technique that provides access to time-dependent infrared spectra in a single shot. Here, we present a spectrometer based on dual-frequency-comb spectroscopy using mid-infrared frequency combs generated by quantum cascade lasers. Attenuation of the intensity of the combs by molecular vibrational resonances results in absorption spectra covering 55 cm in the fingerprint region. The setup has a native resolution of 0.3 cm, noise levels in the μOD range, and achieves sub-microsecond time resolution. We demonstrate the simultaneous recording of both spectra and transients of the photoactivated proton pump bacteriorhodopsin. More importantly, a single shot, i.e., a single visible light excitation, is sufficient to extract spectral and kinetic characteristics of several intermediates in the bacteriorhodopsin photocycle. This development paves the way for the noninvasive analysis of enzymatic conversions with high time resolution, broad spectral coverage, and minimal sample consumption.

Dual-comb spectroscopy for high-temperature reaction kinetics

“…Two frequency combs can be combined to help interpret the signal of multiple wavelengths simultaneously, a technique called dual-comb spectroscopy (DCS). Notable studies involving DCS include: the first dual-comb field diagnostic monitoring greenhouse gases [2], dual-combs in a rapid compression machine [8], and DCS used to study protein dynamics [10].…”

Terahertz hyperspectral imaging with dual chip-scale combs

“…This is especially advantageous when considering spectroscopy of liquids or solids where a trade-off between the GHz-range frequency resolution and the high optical power per mode can be justified. Several examples of chipscale semiconductor laser-based DCS have been demonstrated in the mid-infrared [26][27][28][29] and THz [25] with peak SNRs of more than 10 4 /√s [27,29].…”

Vibrational Stark Spectroscopy of Fluorobenzene Using Quantum Cascade Laser Dual Frequency Combs

“…Experiments were performed with a table-top dual frequency comb spectrometer (IRsweep IRis-F1). 30,31 The dual-comb system (Figure 1 -left) is based on two free-running quantum cascade laser (QCL) frequency combs that individually span over 70 cm -1 and are centered at ~1220 cm -1 . 32 The combs overlap in the 1180 to 1230 cm -1 region which results in dualcomb absorption spectra covering 55 cm -1 with 0.3 cm -1 sampling.…”

“…The latter acquisition scheme was chosen at the time the experiments were performed since the DCS was optimized for single shot experiments reported previously. 30,31 However, it is the most obvious aspect for future improvement and current attempts are focused on improving the balance between acquisition and "dead time". It is therefore interesting to compare the SNR values of both instruments in terms of acquisition time.…”