Gold nanoparticles mediated label-free capacitance detection of cardiac troponin I

It has been already proved that electrical capacitance increases at the electrode surface due to binding of highly charged antigens on the biointerface. In this paper, this capacitance change was used to demonstrate a novel detection for cardiac troponin I (cTnI). Citrate-capped gold nanoparticles (GNPs) were deposited on screen printed electrodes using an innovative one-step electrochemical technique. The gold (Au) nanostructuration onto the electrode surface was characterized by atomic force and field emission scanning electron microscopies. The highly specific anti-cTnI antibodies were immobilized onto the Au matrix, and characterized by confocal microscopy. The interaction of cTnI with its corresponding antibody was studied with respect to electrical capacitance changes as deduced by using the Randles model of the equivalent circuit of the electrochemical cell. The sensor-to-sensor measurements error was registered less than 2% on the average measured capacitance. cTnI was successfully detected in a label-free manner with a limit of detection equal to 0.2 ng mL−1. This obtained result was one order of magnitude better than that obtained with ELISA tests performed by using the same antibodies, with a detection limit of 4.3 ng mL−1.