Sensitive immunosensor for the label-free determination of tumor marker based on carbon nanotubes/mesoporous silica and graphene modified electrode.

A novel label-free immunoassay strategy for sensitive detection of α-fetoprotein (AFP) was proposed based on controlled fabrication of single-wall carbon nanotubes (CNTs) inside the channels of mesoporous silica (MPS). The silanol groups on the internal pore walls of MPS were grafted with amino groups, while the silanol groups on the external surface were blocked by trimethylchlorosilane (TMCS). Thus, CNTs and the monoclonal antibodies of AFP (anti-AFP) could be confined inside the mesopores of MPS by the covalent linking of the carboxyl and amino groups. For the preparation of immunosensing electrode, graphene sheets (GS) and anti-AFP/CNTs/TMCS-MPS were coated on the electrode surface based on layer by layer assembly. After dipping the anti-AFP/CNTs/TMCS-MPS/GS/GCE into the sample solution, the immunoconjugates formed after the immunological reaction, which resulted in the increment of spatial blocking and impedance of the immunosensing interface. Thus, the peak current decreased with the increasing concentration of AFP. CNTs inside the mesopores could promote the electron transportation through the pore channel. Meanwhile, modified GS with distinctive conduction capacity could also improve the electrochemical response. Under the optimal experimental conditions, the label-free immunosensor could detect AFP in a linear range from 0.1 to 100 ng mL(-1) with a detection limit of 0.06 ng mL(-1) (3σ).