A fluorescent probe for the discrimination of oxidation states of palladium

Palladium-based catalysts are widely used in pharmaceutical industries, which can sometimes cause palladium contamination in pharmaceutical drug manufacture. It is important to separately quantify the different oxidation states of palladium (Pd⁰ and Pd²⁺) in pharmaceuticals as they react with scavengers differently. Although palladium sensors have been under intense investigation, oxidation state differentiators are very rare. Here, we report a simple porphyrin-coumarin conjugate, PPIX-L2, that can selectively discriminate between the oxidation states of palladium. The reaction of PPIX-L2 with Pd⁰ showed a 24-fold fluorescence increase of the coumarin emission, meanwhile, the presence of Pd²⁺ led to a 98% quenching of the porphyrin emission. Fluorescent responses of PPIX-L2 towards Pd⁰ and Pd²⁺ are specific, and its sensitivity towards both palladium species is significantly increased with a detection limit of 75 nM and 382 nM for Pd⁰ and Pd²⁺ respectively.