Thionine-doped nanometer-sized silica conjugated with phenylboronic acid: An innovative recognition/signal element for voltammetric aptasensing of colorectal cancer-related carcinoembryonic antigen.

This work reports the proof-of-concept of novel and powerful enzyme-free voltammetric aptasensor of colorectal cancer-related carcinoembryonic antigen (CEA) without the participation of any antibodies. The aptasensor was prepared by means of immobilizing thiolated CEA aptasensor on gold nanoparticle-deposited glassy carbon electrode. Thionine-doped silica nanoparticles were synthesized via reverse micelle method and functionalized with p-aminophenylboronic acid by the epoxy-amino reaction for specific conjugation of subsequent CEA glycoprotein. In the presence of target CEA, the analyte initially reacted with immobilized aptamer on the electrode to generate an aptamer-CEA complex. Then, phenylboronic acid immobilized on silica nanoparticle specifically recognized with CEA glycoprotein based on sugar-boronic acid interaction to form a sandwich-type complex on the electrode. Within the applied potentials, the doped thionine molecules into the silica nanoparticles were used as the electron mediators to produce well-defined voltammetric signals (vs. Ag/AgCl). Under optimum conditions, the voltammetric peak current increased linearly within the CEA concentration in the range from 1.0 pg mL-1 to 10 ng mL-1, and the limit of detection was 0.49 pg mL-1 at 3δ. A repeatability and intermediate precision of ≤8.7% was accomplished at CEA levels in the batch-to-batch mode. The method was highly specific for CEA over other disease-related biomarkers. The accuracy and inter-laboratory validation of this system were evaluated for target CEA detection in human serum specimens, and the results were in accordance with those obtained by a commercial ELISA.