Single-layer Rh nanosheets with ultrahigh peroxidase-like activity for colorimetric biosensing

When the dimensionality of layered compounds decreases to the physical limit, ultimate two-dimensional (2D) anisotropy and/or quantum confinement effects may lead to extraordinary physicochemical attributes. Here, we report single-layer Rh nanosheets (NSs) exhibiting ultrahigh peroxidase-like activity, far exceeding that of horseradish peroxidase (HRP) and of most known layered nanomaterial-based peroxidase mimics. Considering per NS as an active subunit, the Rh NSs displayed a catalytic rate constant (Kcat) as high as 4.45 × 105 s–1 to H2O2, two orders of magnitude higher than those of HRP and Rh nanoparticles. The high atom efficiency of the Rh NSs can be attributed to the full exposure of surface-active Rh atoms, which greatly facilitates electron transfer and formation of superoxide anions, representing reactive oxygen species in the catalytic process. As a proof-of-concept application, the Rh NSs were successfully used as peroxidase mimics for the colorimetric detection of H2O2 and xanthine, with high sensitivity and selectivity. Moreover, a simple, rapid, and sensitive Rh-based paper sensor for ascorbic acid was also developed. In summary, this work provides a novel example of single-layer metallic NSs for biosensing.