Although palladium catalysts are powerful reagents in organic synthesis, hazardous palladium is often found in reaction products even after purifications. Thus, the detection of palladium is an important process in the production of fine chemicals and active pharmaceutical ingredients. We have developed a highly sensitive fluorescent sensor that is capable of detecting 1 ng of palladium quantitatively with the naked eye. Using this method, we were able to selectively detect palladium contamination in aspirin tablets (10 ppm Pd in 1 mg aspirin; mixed in the laboratory for this study), on the surface of flasks previously exposed to palladium, and in rocks containing palladium.