Compact tape-driven sample delivery system for serial femtosecond crystallography

We have developed a compact tape drive (CoT) with on-demand sample delivery for time-resolved serial femtosecond crystallography (SFX) experiments, which can deliver sample droplets and/or initiate reactions with a drop-on-drop strategy. Two disposable piezoelectric injectors are positioned in tandem along the tape to produce a queue of nanolitre-scale droplets. X-ray free-electron laser pulses arrive perpendicular to and pass through the broad face of the tape. The pulse is synchronized and aligned to the droplets, thereby enabling highly efficient SFX data collection. The tape transport speed and the delivery distance can be varied to control the mixing time from approximately 130 ms to tens of seconds. We conducted time-resolved SFX experiments utilizing a basic enzymatic reaction model of hen egg white lysozyme (HEWL) and N-acetyl-D-glucosamine (GlcNAc) to demonstrate the drop-on-drop capabilities of the CoT, and the full binding process of GlcNAc to HEWL was observed at 1.3-9.7 s.