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Selective determination of dopamine using quantum-sized gold nanoparticles protected with charge selective ligands.

We report here the selective determination of dopamine (DA) using quantum-sized gold nanoparticles coated with charge selective ligands. Glutathione protected gold nanoparticles (GS-Au(25)) were synthesized and immobilized into a sol-gel matrix via thiol linkers. The GS-Au(25) modified sol-gel electrode was found to show excellent electrocatalytic activity towards the oxidation of DA but no activity towards the oxidation of ascorbic acid. The role of electrostatic charge in the selective electrocatalytic activity of GS-Au(25) was verified by voltammetry of redox markers carrying opposite charges. The pH dependent sensitivity for the determination of DA further confirmed the charge screening effect of GS-Au(25). Mechanistic investigation revealed that the selectivity is attained by the selective formation of an electrostatic complex between the negatively charged GS-Au(25) and DA cation. The GS-Au(25) modified sol-gel electrode also showed excellent selectivity for DA in the presence of an interferent, ascorbic acid.