Serial femtosecond crystallography has opened up many new opportunities in structural biology. This work presents a drop-on-drop sample delivery system enabling the study of enzyme-catalyzed reactions in microcrystal slurries. The system delivers ligand solutions in picoliter-sized drops onto a larger crystal-containing drop, inducing turbulent mixing and transporting the mixture to the X-ray interaction region. Rapid ligand diffusion is demonstrated using fluorescent dyes, numerical simulations, and time-resolved serial femtosecond crystallography. The method is potentially widely applicable to serial crystallography studies, particularly of enzyme reactions with small molecule substrates.

Agata Butryn, Philipp S. Simon, Pierre Aller, Philip Hinchliffe, Ramzi N. Massad, Gabriel Leen, Catherine L. Tooke, Isabel Bogacz, In-Sik Kim, Asmit Bhowmick, Aaron S. Brewster, Nicholas E. Devenish, Jürgen Brem, Jos J. A. G. Kamps, Pauline A. Lang, Patrick Rabe, Danny Axford, John H. Beale, Bradley Davy, Ali Ebrahim, Julien Orlans, Selina L. S. Storm, Tiankun Zhou, Shigeki Owada, Rie Tanaka, Kensuke Tono, Gwyndaf Evans, Robin L. Owen, Frances A. Houle, Nicholas K. Sauter, Christopher J. Schofield, James Spencer, Vittal K. Yachandra, Junko Yano, Jan F. Kern, Allen M. Orville