An electrochemical sandwich immunosensor of vascular endothelial growth factor based on reduced graphene oxide/gold nanoparticle composites

•The anti body used for nano probe preparation was recombinant Pichia pastoris expressing anti-VEGF Fab fragments.•For simple and fast immobilization of anti body on the surface of electrode we used reduced/graphene oxide/Au nano particles.•Wide linear range and very low limit of detection are some features of prepared nano probe. An electrochemical immunosensor is described for the detection of vascular endothelial growth factor–A (VEGF). Anti VEGF antibody was obtained from Pichia pastoris through expressing the nucleotide sequence. To self-assembly decoration of anti-body on the surface of the electrode, reduced graphene oxide/Au nanoparticles (RGO/Au NPs) was used that caused increase the conductivity and active surface area of the electrode. Instrument characterization were used for structural analysis of RGO/Au NPs. The results show that Au NPs distributed on the surface of RGO sheets uniformly with an average size of 60 nm. Different electric signal transduction modes were used to study the electrochemical performance of the prepared nanoprobe for the detection of VEGF. For the determination of VEGF in buffer media, another anti-VEGF antibody conjugated with Horseradish peroxidase as a secondary antibody that attached and made a sandwich probe on the surface of the electrode was used. Electrochemical studies show that the nanoprobe has suitable selectivity among other biological macromolecules and a good electrochemical response to Anti VEGF by limit of detection about 6 fg.ml−1.