Nanostructures used in impedimetric immunosensors include metallic nanoparticles (NPs) or nanorods such as Au, Ag and Pt, as well as metal oxide NPs; magnetic NPs such as Fe 2 O 3 ; and carbon-based nanostructures such as carbon nanotubes (CNTs), carbon nanodots and graphene. As well as being used as dopants for conducting polymers, nanostructures can also be utilised to amplify the electrochemical signal by acting as a label for the target biomolecule. However, as this work focuses on label-free detection, this section will focus on nanostructures used for electrode modifications prior to biomolecule immobilisation. Nanoparticles will provide a larger surface-tovolume ratio, often leading to an increase in sensitivity, as it will increase the amount of the biorecognition element on the electrode surface.