An ultraviolet fluorescence-based method for identifying and distinguishing protein crystals

Intrinsic ultraviolet fluorescence has been investigated as a rapid non-invasive method for identifying and distinguishing protein crystals. An epi-fluorescence microscope, which provides for excitation and viewing of fluorescence from above the sample, and a straight-through geometry, which provides excitation from above and views fluorescence from underneath the sample, were tested with protein and nonprotein crystal samples. In both systems the protein crystals were observed to fluoresce brightly, providing a high contrast against background solution fluorescence, thus enabling protein crystals to be identified and distinguished from nonprotein crystals.