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 Tb3+ 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.