A label-free immunosensor based on modified mesoporous silica for simultaneous determination of tumor markers

A label-free multiplexed immunoassay strategy was proposed for the simultaneous detection of two tumor markers, carcinoembryonic antigen (CEA) and a-fetoprotein (AFP). Monoclonal antibody of CEA was co-immobilized with ferrocenecarboxylic acid (FCA) inside the channels of mesoporous silica (MPS) to prepare the label-free probe for CEA. Also, monoclonal antibody of AFP was co-immobilized with horseradish peroxidase (HRP) inside the channels of MPS to prepare the label-free probe for AFP by using o-phenylenediamine (OPD) and H2O2 as the electrochemical substrates. Thus, the multianalyte immunosensor was constructed by coating the probes of CEA and AFP respectively onto the different areas of indium-tin oxide (ITO) electrode. When the immunosensor was incubated with sample antigens, CEA and AFP antigens were introduced into the mesopores of MPS after the immunoassay reaction. Because all of the Si-OH groups on the external surface of MPS were blocked with Si(CH3)(3), the proteins and substrates were limited to be embedded on the internal pore walls. Therefore, the electric response transfer was confined inside the pore channels. The nonconductive immunoconjugates blocked the electron transfer and the peak responses changed on the corresponding surface respectively. Then, the simultaneous detection of CEA and AFP achieved. The linear ranges of CEA and AFP were 0.5-45 ng mL(-1) and 1-90 ng mL(-1) with the detection limits of 0.2 ng mL(-1) and 0.5 ng mL(-1) (S/N = 3), respectively. The fabricated immunosensor shows appropriate sensitivity and offers an alternative to the multianalyte detection of antigens or other bioactive molecules. (C) 2011 Elsevier B.V. All rights reserved.