Reduced graphene oxide/nile blue/gold nanoparticles complex-modified glassy carbon electrode used as a sensitive and label-free aptasensor for ratiometric electrochemical sensing of dopamine.

In this work, glassy carbon electrode (GCE) surface was modified by drop-coating graphene oxide (GO) and nile blue (NB) to form GO/NB/GCE. By using a one-step coreduction treatment under cyclic voltammetry (CV) scanning, gold nanoparticles (AuNPs) were electrodeposited onto GO/NB/GCE surface, simultaneously generating reduced GO (rGO). AuNPs from the prepared rGO/NB/AuNPs/GCE was combined with 5'-SH-terminated aptamer of dopamine (DA) via Au-S coupling to fabricate aptamer-rGO/NB/AuNPs/GCE system. DA specifically combined with its aptamer modified on rGO/NB/AuNPs/GCE surface. CV, electrochemical impedance spectroscopy, square wave voltammetry responses of this system as the working electrode were measured. With the addition of DA, the peak current intensities located at -0.45 V (INB ) and 0.15 V (IDA ) showed gradually decreased and increased changes, respectively. There was a good linear (R2  = 0.9922) relationship between lg(IDA /INB ) and the logarithm of DA concentration (lgCDA ) in the CDA range from 10 nM to 0.2 mM, showing a low detection limit of 1 nM. This system as a novel, sensitive and label-free aptasensor was used for ratiometric electrochemical sensing of DA. Experimental results verified that this aptasensor possessed high stability, selectivity and sensitivity towards DA detection, over potential interferents. This aptasensor efficiently determined DA in real biological samples, together with high detection recoveries of 97.0-104.0%.