A standard descriptor for fixed-target serial crystallography

Abstract

Fixed-target crystallography has become a widely used approach for serial crystallography at both synchrotron and X-ray free-electron laser (XFEL) sources. A plethora of fixed targets have been developed at different facilities and by various manufacturers, with different characteristics and dimensions and with little or no emphasis on standardization. These many fixed targets have good reasons for their design, shapes, fabrication materials and the presence or absence of apertures and fiducials, reflecting the diversity of serial experiments. Given this, it would be a Sisyphean task to design and manufacture a new standard fixed target that would satisfy all possible experimental configurations. Therefore, a simple standardized descriptor to fully describe fixed targets is proposed rather than a standardized device. This descriptor is a dictionary that could be read by fixed-target beamline software and straightforwardly allow data collection from fixed targets new to that beamline. The descriptor would therefore allow a much easier exchange of fixed targets between sources and facilitate the uptake of new fixed targets, benefiting beamlines, users and manufacturers. This descriptor was first presented at, and was developed following, a meeting of representatives from multiple synchrotron and XFEL sources in Hamburg in January 2023.

Keywords: fixed targets; serial crystallography; standardization.

Figure 1

A schematic model of a fixed target highlighting the principal components. Design and construction courtesy of Gabriel R. de Sanctis.

Figure 2

Schematic of a fixed target with the parameters labelled. (a) shows the entire fixed target, which comprises 64 city blocks with outer dimensions of approximately 30 × 30 mm. Each city block contains 400 apertures. There is a fiducial marker for alignment at each corner of the fixed target. (b) highlights a subregion of the fixed target showing a single city block. Distance values for this and other fixed targets are given in Table 2 ▸.

Figure 3

Complete standard description of the fixed target shown in Fig. 2 ▸.