Fast fluorescence techniques for crystallography beamlines

Abstract

This paper reports on several developments of X-ray fluorescence techniques for macromolecular crystallography recently implemented at the National Institute of General Medical Sciences and National Cancer Institute beamlines at the Advanced Photon Source. These include (i) three-band on-the-fly energy scanning around absorption edges with adaptive positioning of the fine-step band calculated from a coarse pass; (ii) on-the-fly X-ray fluorescence rastering over rectangular domains for locating small and invisible crystals with a shuttle-scanning option for increased speed; (iii) fluorescence rastering over user-specified multi-segmented polygons; and (iv) automatic signal optimization for reduced radiation damage of samples.

Figure 1

Implementation of on-the-fly fluorescence scanning. ‘CS’ denotes coordinate system.

Figure 2

Fit of the absorption edge position using coarse energy scan data.

Figure 3

Scan tab layout of the JBluIce GUI. The Interactive mode of operation is shown. The right pane displays a fluorescence spectrum with user-adjustable ROI margins marked by the two bars (step 5).

Figure 4

Automatic scanning controls on the Scan tab of the JBluIce GUI. The right pane displays the periodic table from which an edge of interest is selected.

Figure 5

Comparison of (a) the step mode and (b) the shuttle on-the-fly mode of fluorescence rastering for a properly tuned horizontal drive. The cell and the beam size are 20 µm.

Figure 6

JBluIce controls for fluorescence rastering. The right pane shows the result of rastering over a polygon shape.