Dopamine-, l-DOPA-, Adrenaline-, and Noradrenaline-Induced Growth of Au Nanoparticles:  Assays for the Detection of Neurotransmitters and of Tyrosinase Activity

The neurotransmitters dopamine (1), l-DOPA (2), adrenaline (3), and noradrenaline (4) mediate the generation and growth of Au nanoparticles (Au-NPs). The plasmon absorbance of the Au-NPs allows the quantitative colorimetric detection of the neurotransmitters. Neurotransmitters 1, 2, and 4 are sensed with a detection limit of 2.5 × 10^-6 M, whereas the detection limit for analyzing 3 corresponds to 2 × 10^-5 M. The neurotransmitter-mediated growth of the Au-NPs is also used to probe the activity of tyrosinase. The later biocatalyst oxidizes tyrosine to l-DOPA that mediates the growth of the Au-NPs. The analysis of tyrosinase activity is important for detecting melanoma cells and Parkinson disease.