Graphene oxide reduced directly by redox probes for multiplexed detection of tumor markers

Redox probe modified reduced graphene oxide was fabricated through directly reducing graphene oxide using redox probes (toluidine blue (TB) or amino-functionalized ferrocene (NH₂-Fc)). Self-assembling gold nanoparticles to fabricate redox probe modified reduced graphene oxide-Au nanocomposites via electrostatic interaction was then carried out. A sandwich-type electrochemical immunosensor, for simultaneous multianalyte detection (carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP) as model analytes), was designed. Redox probe modified reduced graphene oxide-Au nanocomposites are used as immunosensing probes and an ionic liquid functionalized reduced graphene oxide-Au (IL-rGO-Au) nanocomposite is used as an immunosensing substrate. The resulting immunosensor exhibited high selectivity and sensitivity during the simultaneous determination of CEA and AFP in a single run. The linear ranges were from 0.01 to 100 ng mL^-1 for both CEA and AFP and the detection limits reached 0.003 ng mL^-1 for CEA and 0.002 ng mL^-1 for AFP. Importantly, the proposed immunosensor was evaluated for the analysis of clinical serum samples, producing a good correlation with the data determined by the ELISA. This indicates that the immunosensor provides a possible application for the simultaneous multianalyte determination of CEA and AFP in clinical diagnostics.