Electrochemical Impedance Spectroscopy (EIS) Based Label-Free Immunosensors

Electrochemical Impedance Spectroscopy (EIS) is a surface sensitive technique which examines the impedance of an electrochemical cell over a range of frequencies. By immobilising an antigen or antibody to the electrode surface, EIS shows potential for highly specific and sensitive immunosensor performance. Following an introduction into antibodies and EIS, this review presents immobilisation techniques for an immunosensor’s bioreceptor. It highlights electrode modifications such as self-assembled monolayers (SAMs), polymers and nanostructures for anchoring the bioreceptor to the surface. Stable immobilisation directly to these modifications is not always possible. Immobilisation techniques to these modified surfaces are explored including cross-linking and controlled orientation. EIS allows for label-free detection by monitoring the change in charge-transfer resistance or capacitance caused by changes in the electrode surface. Label-free immunosensors are the focus of this paper as they show potential for point-of-care (POC) devices.