Scheme 2. Selective functionalization of a PCysMA brush for covalent attachment of His-tagged proteins. (a) Schematic representation of the reaction of a PCysMA brush with excess glutaraldehyde in a poor solvent (THF). (b) Exploiting spatial functionalization with glutaraldehyde to produce protein-conjugated PCysMA brushes. (i) PCysMA brushes reacted with glutaraldehyde in THF for 20 h at 22 °C. (ii) First, reaction of aldehyde-functionalized PCysMA brushes with N_α,N_α-bis(carboxymethyl)-l-lysine hydrate (NTA) in water at pH 8.0 for 2 h at 22 °C to give NTA-functional brushes. Second, complexation of the NTA group with Ni²⁺ ions by exposure to a 1 M NiCl₂ solution for 12 h at 22 °C. Third, attachment of His-tagged protein (green fluorescent protein, GFP or proteorhodopsin, pR) by incubation with 0.01 g dm^–3 protein in PBS (pH 7.2) for 12 h at 4 °C. Brushes were washed and dried between each step. After the protein conjugation step, the protein-labelled brushes were kept hydrated by PBS and stored in the fridge at 4 °C prior to use in order to avoid denaturation of the protein.