Furthermore, once 4-ATP is bound to the electrode surface, it can be electrochemically oxidised to form a radical cation, which head-to-tail couples to the neighbouring 4-ATP to 4′-mercapto-Nphenylquinone diamine which is still bound to the surface via the terminal sulphur. Further cycling can oxidise this dimer and even hydrolyse it to form 4′-mercapto-N-phenylquinone monoamine. Cysteamine and cystamine have also been popular monolayers for biosensor applications , despite their short carbon chain which yields insufficient interchain stabilisation. Wirde et al. found cystamine had an approximate 80% surface coverage of that for a C 18 thiol monolayer after 5 mins and with longer adsorption times this coverage increased to approach that of the long chain thiol.