The initiator-functionalized substrates are placed on a flat surface and a desired volume (typically 100 µL per substrate of 1 cm 2 ) of 'ATRP cocktail' is mixed with an amount of ascorbic acid stock solution in an Eppendorf tube. An immediate color change from very light blue to light orange confirms the reduction of Cu(II) to Cu(I). After pipette mixing, the drops of the solution are deposited on the substrates and covered with a glass coverslip, taking care not to trap any air bubbles, as these will create local defects in the resulting brush. The substrates are covered with a petridish to minimize air currents and left to polymerize for the desired amount of time. To terminate the polymerization, the