Microscale reactor embedded with Graphene/hierarchical gold nanostructures for electrochemical sensing: application to the determination of dopamine.

An integrated electrochemical sensing platform is presented, in which stable graphene nanosheets are entrapped within hierarchical gold nano/micro islands (NMI) for the selective detection of dopamine. The fabrication method, which combines lithography, electrodeposition and liquid exfoliation, results in a microscale fluidic reactor capable of handling small volumes (10 μl) of sample. This configuration has advantageous properties, including enhanced sensitivity towards current responses from redox reaction of dopamine to dopamine orthoquinone. The NMIs'spatial orientation inhibits the agglomeration of graphene, while their nanostructured interface enhances adhesion to graphene nanosheets. In turn, this leads to an enlarged surface and to an accumulation of free electrons on the electrode surface. The superior electrocatalytic activity for dopamine is attributed to the high density of π-electrons on graphene nanosheets. In addition, the selectivity of the assay in the presence of other interferents is assumed to be a result of the sp2 π-interactions between the negatively charged graphene layer and the aromatic rings of dopamine. At a working potential of 0.15 V vs Ag/AgCl, the assay has a detection limit of 1.13 nM, a linear range of 1 nM- 100 μM, and apparent recoveries of 106% in spiked synthetic urine. Graphical abstractSchematic presentation of an integrated electrochemical sensing platform, in which stable graphene nanosheets are entrapped within hierarchical gold nano/micro islands (NMI) for selective detection of dopamine. Platinum (Pt) wire and Silver/Silver-Chloride (Ag/AgCl) were used as counter and reference electrode, respectively.