Enhancement of carcinoembryonic antibody immobilization on gold electrode modified by gold nanoparticles and SiO2/Thionine nanocomposite

A reagentless amperometric immunosensor based on antibody-embedded gold nanoparticles (nano-Au) and SiO2/Thionine nanocomposition self-assembled layers was successfully prepared in this work. l-cysteine (Cys) was first modified on a bare gold electrode by potential cycling to prepare a uniform orientation self-assembled monolayer (SAM) with functional groups of –NH2. Then two-double gold nanoparticles (nano-Au) layers were constructed by introducing SiO2/Thionine nanocomposition as linker. Last carcinoembryonic antibody (anti-CEA), as immunoreagent model, was immobilized onto the nano-Au, SiO2/Thionine nanocomposition and nano-Au self-assembled sandwiched layers. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used for the characterization and electrochemical properties of the composite film. By optimization of assay conditions on adsorption time on the first nano-Au layer, the pH of HAc–NaAc buffer, temperature and incubation time, the proposed electrode was proven to be sensitive and specific to detect carcinoembryonic antigen (CEA) between 1.00 and 100.00 ng/mL with a detection limit of 0.34 ng/mL, which was well within the normal physiological range. The capability of the modified electrode for direct CEA quantification in human blood serum was also discussed.