Protein dynamics observed by tunable mid-IR quantum cascade lasers across the time range from 10 ns to 1 s

Abstract

We have developed a spectrometer based on tunable quantum cascade lasers (QCLs) for recording time-resolved absorption spectra of proteins in the mid-infrared range. We illustrate its performance by recording time-resolved difference spectra of bacteriorhodopsin in the carboxylic range (1800–1700cm−1) and on the CO rebinding reaction of myoglobin (1960–1840cm−1), at a spectral resolution of 1cm−1. The spectrometric setup covers the time range from 4ns to nearly a second with a response time of 10–15ns. Absorption changes as low as 1×10−4 are detected in single-shot experiments at t>1μs, and of 5×10−6 in kinetics obtained after averaging 100 shots. While previous time-resolved IR experiments have mostly been conducted on hydrated films of proteins, we demonstrate here that the brilliance of tunable quantum cascade lasers is superior to perform ns time-resolved experiments even in aqueous solution (H2O).