Instantaneous Magnetically Assembled and Hydrophilic Photonic Crystals with Controlled Diffraction Colors

The time-consuming assembling process of the traditional photonic crystals (PCs) and non-water-dispersibility of the reported magnetic responsive PCs (MRPCs) have greatly limited the application especially in the biotechnological fields. Herein, the hydrophilic and size -controllable Fe3O4@poly(4-styrenesulfonic acid-co-maleic acid) (PSSMA)@SiO2 MRPCs were fabricated by orderly assembling of the core-shell colloidal nanocrystal clusters via a twostep facile synthesis approach. Due to the rich carboxyl and hydroxyl groups of PSSMA, the obtained MRPCs have excellent properties of hydrophilicity, high surface charge which presented magnetically tunable photonic structural colors, and rapid reflection signal in aqueous solution under external magnetic field within 1 s. The diffraction color of the MRPCs in the entire visible range could be tuned by adjusting the magnetic strength or the nanoparticle size, which bring a clear change of the structure color from brilliant red to modena by the naked eye. Thus, the magnetically sensitive MRPCs with low-cost, tunable size, and fast optical signal response indicate a promising application in optical systems, biosensors, and biomedical imaging.