Boronic acid functionalized magnetic composites with sandwich-like nanostructures as a novel matrix for PDGF detection

In this paper, we present a novel multifunctional magnetic composite with sandwich-like nanostructure, which is composed of a yolk-egg-like magnetic silica core and a continuous polydopamine(PDA)-Au coating. Firstly, yolk-egg-like magnetic composite(SiO 2 @Fe 3 O 4 @PDA) was prepared by a combined high temperature decomposition method with mussel chemistry. Then, Au nanoparticles(NPs) were in-situ generated on the surface of the SiO 2 @Fe 3 O 4 @PDA by reaction between the PDA shell and HAuCl 4 , forming a multilayer sandwich-like nanostructure. Benefiting from the good affinity of the PDA shell and Au NPs with thiol group, the 4-mercaptophenylboronic acid was successfully assembled on the surface of Au NPs and PDA layer. The hybrid magnetic composite functionalized with boronic acid was used as affinity probes to selectively capture PDGF from solution. Meanwhile, methylene blue(MB)-doped silica NPs (SiO 2 -MB) were prepared to immobilize aptamer. In the presence of PDGF, the aptamer labeled SiO 2 -MB (SiO 2 -MB-aptamer) specifically bound with the PDGF protein. By monitoring the change of the electrochemical signal of MB, we were able to detect the binding events between the aptamer and PDGF in homogeneous solutions. The sensor was highly selective and sensitive with a detection limit of 0.22 fM for PDGF. The developed method showed wide potential applications in protein monitoring and cancer diagnosis.