Calcium Carbonate Storage in Amorphous Form and Its Template-Induced Crystallization

Calcium carbonate crystallization in organisms often occurs through the transformation from the amorphous precursor. It is believed that the amorphous phase could be temporarily stabilized and stored, until its templated transition to the crystalline form is induced. Here we develop a bioinspired crystallization strategy that is based on the above mechanism. Amorphous calcium carbonate (ACC) spherulitic particles are induced to form on a self-assembled monolayer (SAM) of hydroxyl-terminated alkanethiols on a gold surface. The ACC can then be stored in a dry atmosphere as a reservoir for ions and be induced to crystallize on command by the introduction of water and a secondary surface that is functionalized with carboxylic acid-terminated SAM. This secondary surface acts as a template for oriented and patterned nucleation. Various oriented crystalline arrays and micropatterned films are formed. We also show that the ACC phase can be doped with foreign ions (e.g., magnesium) and organic molecules (e.g., dyes) and that these dopants later function as growth modifiers of calcite crystals and become incorporated into the crystals during the transformation process of ACC to calcite. We believe that our strategy opens the way to using a stabilized amorphous phase as a versatile reservoir system that can be converted in a highly controlled fashion to a crystalline form upon contacting a specially designed nucleating template in water.