Functionalized SiO2 labeled CA19-9 antibodies: A new strategy for signal amplification of antigen–antibody sensing processes

Abstract

A new strategy was described for amplifying the response of the antigen–antibody sensing processes by functionalizing SiO₂ nanoparticles labeled secondary antibodies based on a sandwich immunoassay in this work. At first, the multi-walled carbon nanotubes (CNTs) were individually dispersed in the aqueous bovine serum albumin (BSA) to obtain BSA molecules coated CNTs (BSA–CNTs). Then the gold colloids (nano-Au) were absorbed on the BSA–CNTs surface by the amido and disulfide groups of BSA. Later, a functionalized gold/carbon nanotube composite nanohybrid (DpAu/nano-Au/BSA–CNTs) modified electrode was developed by electrochemical deposition of Au³⁺ onto nano-Au/BSA–MWNTs surface. Thus, a sensitive immunosensor for carbohydrate antigen 19-9 (CA19-9) has been constructed by further employment of Nafion coated SiO₂ nanoparticles labeled secondary antibody (SiO₂–Ab₂) for the signal amplification. More importantly, the loading of SiO₂–Ab₂ can not only cause the construction of the dielectric antigen–antibody immunocomplex layer but also introduce the insulated Nafion coated SiO₂ nanoparticles which demonstrate the relatively high resistance, resulting in a strong detection signal. The proposed sensing strategy provides a wide linear dynamic range from 0.15 to 150 U mL⁻¹ with a low detection limit of 0.06 U mL⁻¹ at 3 times the background noise. Moreover, the extremely high stability of the functionalized gold/carbon nanotube composite nanohybrid monolayer allows the designed biosensing interface to obtain a good stability and long-term life.