To confirm the chemistry of the brushes generated, elemental analysis was carried out using XPS (Figures and, and Supplementary Figures and). The wide scan survey of ARGETgenerated PSPMA brushes features the presence of all elements expected from the chemical structure of this polymer, with potassium counterions (Supplementary Figure ). Atom compositions measured were in excellent agreement with those calculated for PSPMA, with a minor discrepancy due to the presence of silicon, presumably owing to defects in the brush coating.