A designer ormosil gel for preparation of sensitive immunosensor for carcinoembryonic antigen based on simple direct electron transfer

The excellent direct electron transfer (DET) of enzyme labeled to antibody immobilized in designer organically modified silicate (ormosil) sol–gel was achieved at an electrode, which was used to construct a novel reagentless immunosensor for antigen determination. The synthesized ormosil architecture provided a hydrophilic interface for retaining the activity of immobilized enzyme labeled immunocomponent. The proposed immunosensor for carcinoembryonic antigen (CEA) prepared by immobilizing horseradish peroxidase-labeled CEA antibody (HRP-anti-CEA) in the architecture showed a surface-controlled electrode process attributed to the DET between electrode and HRP with a rate constant of 5.94 ± 0.40 s⁻¹. The formation of immunocomplex upon incubation in CEA or sample solution led to block of DET and linearly decrease in voltammetric response over CEA concentration ranging from 0.5 to 3.0 and 3.0 to 120 ng ml⁻¹. The limit of detection for CEA was 0.4 ng ml⁻¹. The immunosensor showed good accuracy and acceptable storage stability, precision and reproducibility. The proposed method was simple, low-cost and potentially attractive for clinical immunoassays.