During the electropolymerisation a polymer can be doped with counter ions, which will induce it's conductivity. The π-electron backbone is either oxidised (p-doping) or reduced (n-doping) and the counter anion or cation produce a neutral polymer. Some sections of the chain, referred to polarons and bipolarons, consist of radical cations or dications and act as charge carriers. The doping percentage and type of dopant will influence the level of conductivity. Possible doping ions include camphorsulphonate, tosylate, tetrafuoroborate chloride, perchlorate, sulphate and phosphate. Aniline is typically polymerised using an acid, however buffer solutions with an acidic pH have also proven to be suitable media. using phosphate buffers with pH between 1.7 and 2.2 found some phosphate species to be effective dopants. Hexacyano-ferrate (Fe(CN) 6 ) ions and ferrocene derivatives have successfully been incorporated into polymer layers. This is an attractive dopant due to excellent electrochemical behaviour due to the iron molecule which can undergo reversible electrochemical oxidation. Nanoparticles (NPs) constructed from conductive materials can also be adopted as dopants.