A novel and enzyme-free electrochemical aptasensor based on magnetic separation platform was designed for highly sensitive determination of PDGF-BB by virtue of utilizing catalytic activity of silver nanoparticles (AgNPs) towards the reduction of o-nitrophenol (o-NP) to o-aminophenol (o-AP) by NaBH4, and the ditect electric readout from the product of electrodeposition of o-AP and multiwalled carbon nanotubes (MWCNTs) on screen printed electrode (SPE). Aptamers functionalized magnetic beads (apt-MBs) were used as capture probe, while AgNPs modified with aptamers and hybrid probes (apt-AgNPs-A and apt-AgNPs-B) were used as tags. In the presence of PDGF-BB, the apt-MBs and the AgNPs aggregates which were induced by in-situ hybridization of apt-AgNPs-A and apt-AgNPs-B formed a sandwich-like complex, followed by adding of NaBH4 and o-NP. Owing to the amplified catalysis of AgNPs aggregates conjugated in the complex, the o-NP was reduced by NaBH4 to o-AP, which was electro-co-deposition with MWCNTs on the SPE, producing a conducting nano composite. The signal readout in this aptasensor for PDGF-BB was obtained by direct measurement of the poly(o-AP-MWCNTs) film on the SPE. Using this signal transduction protocol, the analytical performance of the electrochemical aptasensor was studied in detail. Under the optimal conditions, the assay displayed a wide dynamic working range of between 0.1 ng mL(-1) and 100 ng mL(-1) with a detection limit of 60 pg mL(-1) relative to-target PDGF-BB. Incorporation of good catalytic ability of hybridization inducing AgNPs aggregates and excellent electrochemical property of poly(o-AP-MWCNTs) nanocomposite could result in the amplification of the electrochemical signal, owing to the high loading of catalytic AgNPs and electro-co-deposition of MWCNTs. This method would have a promising future for application in clinical diagnostics. (C) 2016 Elsevier B.V. All rights reserved.