An assembled hematin is formed by depositing hematin on an electrically charged substrate in one or more layers alternating with one or more layers of polyelectrolyte, preferably a cationic polymer. In a method for polymerizing an aromatic monomer, the assembled hematin is contacted with the monomer and a template, preferably an anionic polymer. In a method for polymerizing aniline, the aniline, sulfonated multi walled carbon nano tubes, PEG hematin and a reaction initiator are dispersed in water.