Drug Sensing Protein Crystals Doped with Luminescent Lanthanide Complexes

Hen egg white lysozyme (HEWL) crystals are a model system for protein crystallization due to economical production and facile crystal growth. Here we grew small, rod-like HEWL crystals and proceeded with stepwise synthesis to dope the protein crystals with luminescent lanthanide complexes [(Eu(TTA)3phen] (TTA = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato, phen = 1,10-phenanthroline). Several compounds (coumarin, tinidazole, and acridine orange) were observed to quench the lanthanide complexes in solution or embedded within crystals. Coumarin is a precursor for anticoagulant drugs and tinidazole is used to combat bacterial or protozoan infections. In contrast, acridine orange is a widely used, versatile fluorescent dye used to stain acidic vacuoles, RNA, and DNA in living cells. These results suggest that protein crystals may provide a feasible matrix for entrapping luminescent species with practical biosensing applications.