Electrochemical detection of fitness-relevant biomolecules in human saliva

Abstract

For sportsman and fitness enthusiasts the optimization of the training program is a major concern. To improve their daily training routine their fitness, health and stress level has to be tested at least daily and the information has to accessible as fast as possible. This can be achieved with POC devices which measure the level of relevant biomarkers. A saliva based electrochemical sensor was chosen to provide the necessary sensitivity and accessibility for the user. A two-electrode EIS based cortisol-immunosensor is able to detect cortisol from buffered solutions in the necessary sensitivity range, but because of the corrosive properties of the redox-couple ferro-/ferricyanide did not provide the necessary stability of the measurements. Different alternative redox-systems were tested and a three-electrode setup in combination with a DC-bias during the EIS measurement to produce the reduced form of hexaammineruthenium(III) in the solution was chosen. Thin-film produced electrodes on PET and glass, and screen-printedelectrodes on ceramic substrates were tested in a three-electrode setup. Fully functionalised IgG-sensors on PET exhibited a reduced response in comparison to the glass and ceramic based immunosensors. An IgG and cortisol specific sensor was achieved on the ceramic substrate and was sufficiently sensitive for the detection of the biomarkers from saliva, but the IgG sensor on the ceramic substrate exhibited a high intra-batch variation. The intra-batch variation was the lowest with the glass based IgG-sensor. Saliva samples were analysed with the help of the IgG immunosensor on the glass substrate. The results were compared to a commercially available ELISA kit. A two-sample t-test with a confidence level of 0.05 revealed no difference between the results of the electrochemical IgG sensor and the ELISA kit.