Laser-based infrared (IR) spectroscopy is an emerging key technology for the analysis of solutes and for real-time reaction monitoring in liquids. Larger applicable pathlengths compared to the traditional gold standard Fourier transform IR (FTIR) spectroscopy enable robust measurements of analytes in a strongly absorbing matrix such as water. Recent advancements in laser development also provide large accessible spectral coverage thus overcoming an inherent drawback of laser-based IR spectroscopy.

In this work, we benchmark a commercial room temperature operated broadband external cavity-quantum cascade laser (EC-QCL)-IR spectrometer with a spectral coverage of 400 cm⁻¹ against FTIR spectroscopy and showcase its application for measuring the secondary structure of proteins in water, and for monitoring the lipase-catalyzed saponification of triacetin. Regarding the obtained limit of detection (LOD), the laser-based spectrometer compared well to a research-grade FTIR spectrometer employing a liquid nitrogen cooled detector. With respect to a routine FTIR spectrometer equipped with a room temperature operated pyroelectric detector, a 15-fold increase in LOD was obtained in the spectral range of 1600–1700 cm⁻¹. Characteristic spectral features in the amide I and amide II region of three representative proteins with different secondary structures could be measured at concentrations as low as 0.25 mg mL⁻¹. Enzymatic hydrolysis of triacetin by lipase was monitored, demonstrating the advantage of a broad spectral coverage for following complex chemical reactions. The obtained results in combination with the portability and small footprint of the employed spectrometer opens a wide range of future applications in protein analysis and industrial process control, which cannot be readily met by FTIR spectroscopy without recurring to liquid nitrogen cooled detectors.

基于激光的红外（IR）光谱学是一种新兴的关键技术，用于分析溶质和实时监测液体中的反应。与传统的金标准傅里叶变换红外（FTIR）光谱相比，更大的适用光程使得能够对强吸收性基质（例如水）中的分析物进行可靠的测量。激光开发的最新进展还提供了较大的可访问光谱范围，从而克服了基于激光的红外光谱的固有缺陷。

在这项工作中，我们以FTIR光谱为基准，对光谱范围为400 cm ^-1的商业室温操作宽带外腔-量子级联激光（EC-QCL）-IR光谱仪进行了标定，并展示了其在测量蛋白质二级结构中的应用。水，并用于监测脂肪酶催化的甘油三乙酸酯皂化。关于获得的检测限（LOD），基于激光的光谱仪与采用液氮冷却检测器的研究级FTIR光谱仪进行了很好的比较。对于配备了室温操作热释电探测器的常规FTIR光谱仪，在1600-1700 cm ^-1的光谱范围内，LOD增加了15倍。可以在低至0.25 mg mL ^-1的浓度下测量具有不同二级结构的三种代表性蛋白质在酰胺I和酰胺II区的特征光谱特征。监测了脂肪酶对三醋精的酶促水解，证明了其对于后续复杂化学反应的光谱覆盖范围广。所获得的结果与所用光谱仪的便携性和小占位面积相结合，为蛋白质分析和工业过程控制提供了广阔的未来应用范围，而如果不使用液氮冷却检测器，则FTIR光谱无法轻松满足这些要求。