A Quantum Cascade Laser Microscope for Time-resolved Study of Membrane Proteins

We have developed a confocal laser microscope operating in the wavelength range between 5.8 and 6.3 mu m with a parallel confocal visible-light illumination channel for the study of light-sensitive membrane proteins. The measured diffraction-limited lateral resolution is 19 mu m. Differences in the amide-I and II bands of proteins of the order of 10(-5) can be detected with 30 ms time resolution using cryogen-free HgCdTe detectors and lock-in amplification at the QCL repetition rate. The microscope is suitable to study rhodopsins with a slow photocycle of several seconds.