A label-free amperometric immunosensor for alpha-fetoprotein determination based on highly ordered porous multi-walled carbon nanotubes/silica nanoparticles array platform

In this contribution, we develop a novel type of multi-walled carbon nanotubes/silica nanoparticles array (MWCNTs/SiO2) composite by the galvanostatic deposition technique. In this process, MWCNTs were mixed with ammonium fluorosilicate to form a doped precursory sol solution, the electrochemically generated hydroxyl ions at negative potentials promote the hydrolysis of ammonium fluorosilicate, and the simultaneously generated hydrogen bubbles assist the formation of three-dimensional porous silica matrix, further facilitating the construction of SiO2 NPs array with uniform distribution, as confirmed by scanning electron microscopy. The formation of SiO2 NPs array provides a higher surface area and biocompatible microenvironment for retaining the native activity of the immobilized biomolecules. Further incorporation of MWCNTs into SiO2 NPs array improves the electronic conductivity and enhances the electroactive surface area of the film, making the fabricated three-dimensional porous MWCNTs/SiO2 electrode an ideal platform for further immobilization of alpha-fetoprotein (AFP), as a model protein. This method achieves ultrasensitive detection of AFP antigen with ferricyanide as a probe. The obtained results provided a linear response range from 0.1 to 30.0 ng m L-1 AFP antigen with a lower detection limit of 0.018 ng mL(-1). This work implies that the biocompatible and controllable three-dimensional porous SiO2 NPs array possessed potential applications for biosensing. (C) 2012 Elsevier B.V. All rights reserved.