Determination of catecholamines based on the measurement of the metal nanoparticle-enhanced fluorescence of their terbium complexes

We have developed a method for the determination of the three catecholamines (CAs) epinephrine (EP), norepinephrine (NE), and dopamine (DA) at sub-nanomolar levels. It is found that the luminescence of the complexes formed between the CAs and Tb ³⁺ ion is strongly enhanced in the presence of colloidal silver nanoparticles (Ag-NPs). The Ag-NPs cause a transfer of the resonance energy to the fluorophores through the interaction of the excited-state fluorophores and surface plasmon electrons in the Ag-NPs. Under the optimized condition, the luminescence intensity of the system is linearly related to the concentration of the CAs. Linearity is observed in the concentration ranges of 2. 5-110 nM for EP, 2. 8-240 nM for NE, and 2. 4-140 nM for DA, with limits of detection as low as 0. 25 nM, 0. 64 nM and 0. 42 nM, respectively. Relative standard deviations were determined at 10 nM concentrations (for n = 10) and gave values of 0. 98%, 1. 05% and 0. 96% for EP, NE and DA, respectively. Catecholamines were successfully determined in pharmaceutical preparations, and successful recovery experiments are demonstrated for urine and serum samples.