UV Compatible Plates

Not all crystallography consumables are compatible with ultraviolet light. Cover media can either block the excitation light (absorb UV radiation in the 250-320 nm band) or it can fluoresce in the same band that tryptophan does, creating a high level of background noise (this is a process commonly called autofluorescence). Crystallization plates can also autofluoresce, increasing unwanted noise. The challenge of absorption is not a problem in crystallization plates for we have positioned the UV light source and camera of our imagers above the plates.

To recap, there are three consumable-related problems that could reduce the signal-to-noise ratio while imaging using UV light (listed in the order of what seems most common and serious):

• Crystallization plate could autofluoresce, increasing noise (common in polystyrene plates).
• Cover media could absorb some/all of the UV excitation light, reducing the signal strength (This can be partially recovered with longer exposure times).
• Cover media could autofluoresce, increasing noise (common in glass cover slides).