Silver nanoparticles enhanced luminescence of terbium complex in solution for L-dopa determination

Luminescent properties of a terbium (Tb3+)-L-3, 4-dihydroxyphenylalanine (L-dopa) complex by binding to colloidal silver nanoparticles (Ag NPs) have been presented. Luminescence intensity of the L-dopa complex was dramatically enhanced about 6-7 times by introducing Ag NPs. The Ag NPs concentration on the luminescent intensity was regarded as a main factor that balancing between an enhancing and a quenching effect of the Ag NPs. It was observed that changing the concentration of L-dopa causes the change in luminescence intensity. Under the optimized condition, the luminescence intensity of the system was linearly related to the concentration of L-dopa. Based on this observation, L-dopa-Tb3+ complex containing Ag NPs has been applied for the determination of L-dopa in pharmaceutical formulation. Linear responses of luminescence intensity were observed in the concentration range of 0.25 to 1.5 nM (r = 0.9934) of L-dopa with limit of detection 0.042 nM. The performance of the system was tested using 1.0 x 10(-9) M of L-dopa, yielding a precision of 1.21% RSD for nine replicate measurements. The present method has been successfully applied to determine L-dopa in pharmaceutical samples.