Preformed NPs which are adsorbed onto the electrode surface are prepared by the reduction of metal salts in the presence of a protecting agent, such as polyvinylpyrrolidone (PVP), to prevent agglomeration. The deposition time for such NPs could be minutes to days. Electrodeposition presents a faster option for modifying an electrode. This is undertaken at a reducing potential and as with electropolymerisation the chosen parameters will affect the resulting layer. Varying applied potential or current density and deposition time will allow control of the particle size. Alternatively, NPs can be attached to the surface through a molecular linker. There are four options for this linkage as depicted in Figure , all of which require the NP to have a preformed ligand shell. The first method requires the electrode to be pre-functionalised with a SAM, which will act as the molecular linker. The terminal functional group will bind to the NP's ligand shell either through ligand exchange or electrostatic interactions. For example, a SAM layer consisting of MPA and mercaptoethylamine can be anchor Au NPs to an electrode through Au-S bond. Long chain SAMs can act as an insulative layer on the electrode, but the attachment of metallic NPs can facilitate charge transfer. The second method pre-functionalises the electrode surface with an ionically charged polymer. The NP's shell electrostatically interacts with this charged layer. Commonly used polymers for this route to capture NPs includes poly-L-lysine (PLL), poly(diallyldimethylammonium) chloride (PDADMAC), poly(amidoamine) (PAMAM), and poly-L-arginine (PLA), all of which are cationic. The third method is through "click chemistry" which coupling of the functional group on the electrode surface to the functional group on the NP ligand, such as undecyn-1-thiolate with azide through azidealkyne cycloaddition reaction to form a triazole. The fourth method directly binds the NP ligand to the electrode surface. immunosensor for the Alzheimer's biomarker detection of amyloid beta. Their SAM layer of MPA was first assembled onto the gold electrode and then Au NPs where electrodeposited onto the SAM layer using a constant potential. The AuNPs were densely and uniformly distributed, allowing for maximum antibody loading. reported origami paper based impedimetric immunosensor for C-reactive protein (CRP). For the construction of biosensor, researchers applied an electrodeposition protocol in order to obtain gold nanostructures on the electrode surface and then SAMs formation of L-Cysteine was studied onto gold nanoparticles, which was then used as an immobilisation matrix for the anti-CRP antibodies immobilisation via carbodiimide chemistry.