Gold-linked electrochemical immunoassay on single-walled carbon nanotube for highly sensitive detection of human chorionic gonadotropin hormone.

A new sensitive gold-linked electrochemical immunoassay (GLEIA) for the detection of the pregnancy marker human chorionic gonadotropin (hCG) has been developed using the direct electrochemical detection of Au nanoparticles. We utilized single-walled carbon nanotube (SWCNT) microelectrodes; 24 SWCNT microelectrodes were arrayed on a single Si substrate 25×30 mm² in size, for the development of a new GLEIA (SWCNT-GLEIA). This SWCNT-GLEIA provided convenient and cost-effective tests with the required antibody and antigen sample volumes as small as 2.0 μL for a group of 4 SWCNT microelectrodes. In addition, this assay also exhibited properties of high sensitivity and selectivity benefitting from the intrinsic extraordinary features of SWCNTs. Using scanning electron microscopy, we also observed Au nanoparticle-labeled antigen-antibody complexes immobilized on the surface of the SWCNT microelectrodes. The concentration of the pregnancy marker (hCG) showed a linear relationship with the current intensity obtained from differential pulse voltammetry measurements with a limit of detection (LOD) of 2.4 pg/mL (0.024 mIU/mL) hCG. This LOD is 15 times more sensitive than a previous GLEIA, which used screen-printed carbon electrodes.