Biomolecule-based formaldehyde resin microspheres loaded with Au nanoparticles: A novel immunoassay for detection of tumor markers in human serum

• High-yield synthesis of biomolecule (serotonin)-based formaldehyde resin (BFR) microspheres is proposed for the first time.
• The BFR microspheres loaded with Au nanoparticles provide a conductive multi-pathway of electron transfer.
• A sensitive label-free electrochemical immunosensor based on AuNPs/BFR microspheres is used for carcinoembryonic antigen (CEA) determination.
• It is the first CEA biosensor with the use of AuNP/BFR microspheres.
• This immunosensor can be used for CEA detection in human serum.

A surfactant-free and template-free method for the high-yield synthesis of biomolecule (serotonin)-based formaldehyde resin (BFR) microspheres is proposed for the first time. The colloidal microspheres loaded with Au nanoparticles (AuNPs) prepared by a convenient in-situ synthesis of AuNPs on BFR (AuNPs/BFR) microsphere surface show good stability. AuNPs/BFR microspheres not only favor the immobilization of antibody but also facilitate the electron transfer. It is found that the resultant AuNPs/BFR microspheres can be designed to act as a sensitive label-free electrochemical immunosensor for carcinoembryonic antigen (CEA) determination. The immunosensor is prepared by immobilizing capture anti-CEA on AuNPs/BFR microspheres assembled on thionine (TH) modified glassy carbon electrode (GCE). TH acts as the redox probe. Under the optimized conditions, the linear range of the proposed immunosensor is estimated to be from 25 pg/mL to 2000 pg/mL (R=0.998) and the detection limit is estimated to be 3.5 pg/mL at a signal-to-noise ratio of 3. The prepared immunosensor for detection of CEA shows high sensitivity, reproducibility and stability. Our study demonstrates that the immunosensor can be used for the CEA detection in humans serum.