Low biomarker concentrations give signals that are too weak for most electrochemical methods. Redox probes are usually added to amplify the interaction at the electrode surface, but they can degrade electrodes, reduce reproducibility, and damage some biomarkers.
High-frequency impedance spectroscopy is an alternative. A capacitance change of 0.2 pF is not detectable at low frequencies but is resolved in the MHz range, which the ECA-5M covers.
The figure above compares the measured and simulated impedance. The measurement is label-free and needs no redox probe.