We developed a cloneable inorganic nanoparticle (cNP) paradigm (Figure , panel C). This paradigm adapts in vitro reductive iNP synthesis to the in vivo context. With in vitro synthesis, soluble metal cations are reduced (e.g., with BH4 -) to insoluble precipitates in the presence of ligands. Ligands cap these precipitates at iNP size, stopping their growth. For in vivo (cNP) synthesis, the metal(loid) precursors are biocoordination complexes present inside cells. Reduction of precursors is by NAD(P)H dependent metal(loid) oxidoreductases. These enzymes transform cNP precursors into bulk phase precipitates, consuming NADPH. Bio-ligands present in the cellular milieu then cap and arrest the growth of metal(loid) precipitates at nano-sized dimensions. If the bio-ligands are peptides or proteins, they can be fused to the enzyme, which in-turn can fuse the cNP to the enzyme.