Dopamine and ascorbic acid electro-oxidation on Au, AuPt and Pt nanoparticles prepared by pulse laser ablation in water

In this study, we have investigated the use of PtAu alloy nanoparticles (NPs) with four different compositions (from x = 0 to 100) as electrodes for the detection of dopamine (DA) in the presence of ascorbic acid (AA). The Au100-xPtx NPs were prepared by pulsed laser ablation in an alkaline solution without using any surfactants or capping agents. The diameter of the particle ranges from 2.5 nm for pure Pt to 5.2 nm for pure Au NPs. Cyclic voltammetry showed that the number of DA molecules being oxidized on the NPs surface decreases with the Au content (from 9.0 × 10−11 mol on Au to 4.8 × 10−11 mol on Pt NPs), which emphasizes the preponderant role of Au surface sites on the electrochemical oxidation of DA. On the other hand, the oxidation current of AA is greatly enhanced by alloying Au with Pt, and the peak current of the alloyed NPs is about two (Au50Pt50) and four times (Au70Pt30) higher than that of Au NPs. It is suggested that the oxidation of the lateral chain of AA on the Pt sites occurs simultaneously to the oxidation of the ascorbate anion to dehydro ascorbic acid on the Au sites. Finally, it was shown by differential pulse voltammetry that Au and Au100-xPtx NPs can detect DA in solutions containing AA with a concentration 1000× higher. For example, for Au70Pt30 the sensitivity and detection limit for the detection of DA in presence of 2 mM AA were 3.34 μA μM−1 and 0.06 μM (at S/N = 3) respectively, essentially the same values (3.50 μA μM−1 cm−2 and 0.05 μM) as in the absence of AA.