The size range of an atom is approximately 3–5 Å (10−10 m), while a nanometer is 10−9 m. Thus, nanomaterials are used as multipliers that can be used to attach several single atoms to the surface. It is similar to an exquisitely-arranged production line, with every single atom acting as an operator, working on each catalytic reaction. As applied to biological applications, these catalytic targets become proteins in vivo, and the transformation of nanomaterials into single-atom catalytic enzymes illustrates the potential of the new single-atom nanozyme (SAN) nanotechnology for biological applications. As SAN materials on the order of 1 nm–100 nm are selected as carriers, such as carbon quantum dots and metal-organic frameworks, they can load single atoms and make their reaction efficiency much higher than that of regular enzymes. Moreover, the support materials have the optical property of absorbing the radiation that allows the nanocomposite to influence the behavior of the chemical reactions. In this review, we present novel SANs that can both increase the catalytic rate and produce diagnostic and therapeutic effects.