The past four years have witnessed booming progress in single-atom nanozymes (SANs), one of the newest generations of nanozymes with atomically dispersed metal sites for catalytic biomedical uses. They show distinct advantages over their nanoparticle-based counterparts, such as well-defined electronic/geometric structures and complete atomic utilization efficiency, thus offering opportunities to develop advanced nanozymes for practical uses. The atomically dispersed active centers in SANs could also facilitate the precise regulation of catalytic performance, while probing structure–activity relationship for in-depth understanding of mechanism. In this review, we first introduce the synthetic approaches, surface engineering, and characterization techniques of SANs. Subsequently, we discuss the enzyme-like properties of SANs, including some strategies for boosting their catalytic activities. Furthermore, we present their biomedical applications, ranging from biosensors, antibacterial uses, antioxidants, to therapeutics. Finally, the challenges and opportunities of SANs are prospected.

Herein, we present a new strategy that for the first time achieved chemo- and enantio-selective hydrogenation of alkenes over arylhalides. Key to the success is that instead of using external poisons, we use the composition of the bimetallic nanocrystal catalysts to control chemoselectivity (hydrogenation of C=C bonds without cleavage of Ar-X bonds). We further show that this system combined with surface modifying chiral ligands can control the enantioselectivity. Thus, after synthesizing and screening a series of easily accessible M_xAu_y (M = Pd, Pt; x, y = 1, 3, 5) bimetallic nanocrystals (9–10 nm) supported on activated carbon, we identified that Pt₁Au₁/C is a recyclable and generally applicable catalyst for the chemoselective hydrogenation of alkenes without cleaving aryl halogen bonds. Furthermore, cinchonidine modified Pt₁Au₁/C is shown to be capable of enantioselective hydrogenation, as illustrated by the rapid and enantio-enriched synthesis of RIP1 inhibitor analogue 7-Br-O-Nec1.