A simple and label-free aptasensor based on amino group-functionalized gold nanocomposites-Prussian blue/carbon nanotubes as labels for signal amplification

Herein, a novel label-free electrochemical aptasensor based on gold nanoparticles/Prussian blue/carbon nanotubes (AuNPs/PB/CNTs) for dopamine (DA) determination was reported. A special AuNPs/PB/CNTs nanocomposite which integrated the individual properties of each nanomaterial was utilized to improve the conductivity and performance characteristics of the biosensor as well as to increase the loading amount of aptamer. Chitosan was coated onto nanocomposite and provided a biocompatible interface with abundant-NH2 groups for the immobilization of DA-specific aptamer. Abundant-NH2 groups in nanocomposite made this platform as significant transduction by allowing phosphoramidate bonds formed between the amino group of chitosan and phosphate group of the aptamer at 5'end. To translate the binding events between aptamer and DA into the measurable electrochemical signal, the PB as signal probe was in situ introduced on the electrode surface, exhibiting well-defined peaks with good stability and reproducibility. The designed immobilized DA aptamer resulted in the formation of long tunnels on modified electrode-surface, while aptamer acted as gate of the tunnels. The aptamer gates were closed due to change in conformation of aptamer upon target (DA) binding, retarding the interfacial electron transfer reaction of the probe, resulting in the decrease of the electrochemical signal. Under optimized conditions, the proposed aptasensor showed good detection range from 0.5 to 50 nM with unprecedented detection limit of 200 pM. This aptasensor also exhibited good stability and high selectivity for DA detection without an interfering effect of some other compounds. (C) 2016 Elsevier B.V. All rights reserved.