“…[1][2][3][4] Among the commonly used stopped-flow methods (e.g., fluorescence, ultraviolet-visible (UV-Vis) absorbance, far-UV CD, small-angle X-ray scattering, infrared, and Raman), stopped-flow infrared (IR) is particularly appealing because of the high sensitivity of infrared spectroscopy to protein conformations. However, the existing stopped-flow infrared (IR) methods [5][6][7][8][9][10][11] are based on the rapid-scan mode of a Fourier transform (FT) spectrometer; therefore, their timeresolution is limited by the scanning rate of the interferometer (or the mechanical movement of the mirror). Depending on the specific FT-IR spectrometer used, the time resolution of such stopped-flow FT-IR instruments may vary, but it is typically around 60 to 80 ms. 11 While the time resolution can be greatly improved by using the continuous-flow method, 16,17 i.e., to the microsecond time scale, such continuous-flow IR methods suffer from high sample consumption and are normally limited to an observation time window of only a few milliseconds.…”