Ultrasensitive electrochemical immunosensor for CA 15-3 using thionine-nanoporous gold-graphene as a platform and horseradish peroxidase-encapsulated liposomes as signal amplification.

This paper describes a novel electrochemical immunosensor using a nanoporous gold (NPG)/graphene (GN) hybrid platform combined with horseradish peroxidase (HRP)-encapsulated liposomes as labels for the sensitive detection of cancer antigen 15-3 (CA 15-3). The electrochemical detection was based on the released HRP from HRP-encapsulated liposomes toward the reduction of H(2)O(2) with the help of the thionine (TH) electron mediator. In the presence of CA 15-3, HRP@liposomes and TH-NPG-GN formed a sandwich-type immunocomplex, and the immunocomplex increased with the increment of the CA 15-3 concentration in the sample. The more CA 15-3 antigen in the sample there was, the more HRP@liposomes/anti-CA 15-3 in the immunocomplex there were. Thus, the catalytic current increased. Under optimized conditions, the linear range of the immunoassay is 2 × 10(-5) to 40 U mL(-1) with a detection limit of 5 × 10(-6) U mL(-1) CA 15-3. The CA 15-3 concentrations of the clinical serum specimens assayed by the developed immunoassay showed consistent results in comparison with those obtained by a commercially available electrochemiluminescence assay. This proposed immunoassay system had many desirable merits including sensitivity, accuracy, and minimal instrumentation required. Significantly, the new protocol may be quite promising, with potentially broad applications for clinical immunoassays.