Reagentless amperometric cancer antigen 15-3 immunosensor based on enzyme-mediated direct electrochemistry

A novel strategy was proposed for the construction of reagentless and mediatorless immunosensors based on the direct electrochemistry of glucose oxidase (GOD). Firstly, a composite material containing carbon nanotubes (CNTs) and core-shell organosilica@chitosan nanospheres was successfully prepared and cast on the glassy carbon electrode surface directly. Then, Pt nanoclusters (Pt NCs) as an electron relay were deposited on it to form the interface of biocompatibility and huge surface free energy for the adsorption of the first GOD layer. Subsequently, the second Pt NCs layer was deposited on the surface of GOD to capture CA15-3 antibodies (anti-CA15-3). Finally, GOD, as a blocking reagent instead of bovine serum albumin, was employed to block the possible remaining active sites of the Pt NCs and avoid the nonspecific adsorption. The immunosensor with the double layer GOD membranes as tracer performed excellent biocompatible and avoided the pollution of mediator molecules. The immobilized GOD showed direct electron transfer with a rate constant of 4.89 s−1 and the peak current decreased linearly with increasing logarithm of CA15-3 concentration from 0.1 to 160 U/mL with a relatively low limit of detection of 0.04 U/mL at 3σ. Such a detection of immunointeraction provided a new promising platform for clinical immunoassay.