Multi-wavelength transparent microfluidic device for UV-visible illumination and X-ray scattering studies of photoactive systems.

Abstract

Microfluidic devices are increasingly used in synchrotron-based experiments to deliver and probe liquid samples, offering advantages such as minimal sample consumption and reduced radiation damage. Despite their growing use, few devices have been specifically designed for monitoring liquids under photoexcitation, a promising approach for fast structural transitions. Here, a microfluidic device is presented that is transparent to X-rays in one direction and simultaneously transmits UV and visible light illumination to the sample in the perpendicular direction. The device is fabricated using lamination and UV lithography on a dry-film resist, eliminating the need for cleanroom facilities and simplifying production. Its multi-wavelength transparency was validated through UV-vis spectroscopy, where photoexcitation at different wavelengths induced reversible <i>trans</i>-to-<i>cis</i> isomerization of azobenzene and fluoro-azobenzene. X-ray transparency was verified through small-angle X-ray scattering (SAXS) measurements on hemoglobin and CO-ligated hemoglobin, both of which are sensitive to quaternary structural changes. These results confirm the suitability of the device for resolving protein structures and detecting subtle conformational changes of the type commonly encountered in photo-induced modulation. Initial proof-of-concept measurements demonstrate the feasibility of temperature-jump (T-jump) experiments, and the same architecture is readily extendable to time resolved pump-probe studies, providing a versatile platform for studying structural evolution in liquid samples using synchrotron SAXS.