Cathodic electrochemiluminescence at C/CxO1−x electrodes for the fabrication of label-free biosensors

Cathodic electrochemiluminescence (ECL) is firstly observed at a carbon oxide covered glassy carbon (C/CxO1−x) electrode as a large cathodic pulse polarization is applied. This insulating carbon oxide (CxO1−x) film is constructed on a glassy carbon (GC) substrate by electrochemical oxidization in basic media. The film properties, such as the composition of carbon and oxygen, and the thickness as well, can be controlled by the potential and the duration in the oxidizing process. X-Ray photoelectron spectroscopy (XPS) studies show that carbonyl and carboxyl dominate at the oxidized surface, to which antibodies can be covalently bound. The specific immunoreaction between antigen (Ag) and antibody (Ab) resulted in a decrease in the ECL intensity, thus creating an interesting basis for the development of a label-free cathodic ECL immunosensor. As an example, human IgG (hIgG) was sensitively determined in the concentration range of 0.01–100 ng mL−1, and the detection limit was ca. 1.0 pg mL −1 (S/N = 3). In addition, the content of hIgG in human serum has been assayed by the developed immunosensor and a commercially available immune turbidimetry method, respectively, and consistent results were obtained. The prepared immunosensor provides a promising approach for the clinical determination of IgG levels in human serum, because it is simple, rapid, highly sensitive, specific, and without the need of tedious labeling operations.