Tandem-biocatalysis reactors constructed by topological evolution of CaCO 3 particles into hollow metal hydroxide spheres.

Despite remarkable advances in the design and synthesis of hollow inorganic spheres (HISs), the harsh synthetic conditions have precluded the applications of HISs to biochemical and biological fields. Herein we report a biocompatible strategy for synthesizing metal hydroxide HISs (MH-HISs) by simply mixing CaCO 3 particles with metal ions in water. The ion-exchange reaction between Ca 2+ and metal ions leads to the structural and chemical evolution from solid CaCO 3 particles to hollow MH-HISs via core-shell and yolk-shell structures, while enabling the encapsulation of enzymes to the shells without loss of catalytic activities. The biocompatible protocol makes multienzymatic cascade reactions achievable, with great recyclability due to mechanical durability of MH-HISs.