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 non-protein 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 non-protein crystals.