nanosheets. TMDs have an MX 2 layered structure, where the M is a transition metal typically from group IV, V or VI and the X is a chalcogen (S, Se or Te), with the transition metal sandwiched between the chalcogens. There are strong covalent M-X intralayer bonds, while weak van der Waals bonds hold together adjacent layer, which can be cleaved to form nanosheets a few layers thick. Depending on the crystalline structure of the nanosheets, the electronic characteristics can be semiconducting, metallic, or superconducting. BN nanosheets consist of alternating boron and nitrogen atoms in a honeycomb lattice. Due to their hydrophobicity they are generally modified with a polymer such as chitosan or PDADMAC to increase their solubility and stability in aqueous solutions before immobilisation of the bioreceptor. The polymeric g-C 3 N 4 is a nitrogen doped graphene with tris-triazane based units and acts as a semiconductor. Nitrogen is a strong electron donor, changing the electronic structure from graphene, resulting in enhanced electron activity. For instance, the nitrogen atoms disrupt the basal surface, edge plane-like sites which are electrochemically active. The forms of electrode modifications that have been discussed can be combined resulting in a huge range of possible modifications. As mentioned in the previous section polymers are often deposited onto the electrode surface in conjunction with nanostructures, incorporating them into the polymers coating. However, nanostructures are also deposited onto electrodes that have already been modified with a polymer layer and form a second separate layer on top of the polymer. For instance, Narang et al. coated their impedimetric sensor with chitosan and then decorated it with Au nanorods.