Nanoporous gold-based dopamine sensor with sensitivity boosted by interferant ascorbic acid

Abstract

Tuning electrochemical reactivity of nanoporous gold (NPG) by controlling its fabrication parameters is a convenient strategy to realize a selective electroanalytical platform for dopamine (DA), whose detection in real biological samples is hampered by the presence of structurally similar ascorbic acid (AA) typically in 1000-fold excess. Accordingly, a simple strategy was devised to overcome such a problem by exploiting the electrocatalytic properties associated with higher surface energy (220), (200) and (311) Au planes, which are formed in larger amounts as a function of the thickness of the NPG films prepared by an electrodeposition method. Such selectivity in DA electrooxidation could only be retained at thicker NPG films and this was attributed to the higher density of reactive electrocatalytic sites, which enhance the rate of the electron transfer reaction associated to the AA anodic process. Such proposition was confirmed by a comprehensive electron transfer kinetics study by Scanning Electrochemical Microscopy. The current response due to DA oxidation was enhanced by the follow-up chemical reaction between dopamine-o-quinone (the oxidation product of DA) and AA present in large excess, converting a potential interferant into a partner. In this way, detection limit as low as 60 nmol L−1 allied to sensitivity as high as 6.7 μA/μmol L−1 were achieved under up to 10000 times excess of that interferant, demonstrating the high potentiality of such NPG3 modified electrode as a sensor for analyses of DA in real biological samples.