Synergistic Fe–Mo Dual Single-Atom Nanozymes: Enhanced Peroxidase-Like Activity and Colorimetric Detection of <scp>l</scp> -Penicillamine

Single-atom nanozymes have been applied in biosensing. However, their enzyme catalytic activity still needs to be further improved to meet diverse biosensing needs. Here, we develop a hollow cube (HC)-structured Fe 1 Mo 1 dual single-atom nanozyme (Fe 1 Mo 1 –HC) with enriched N 3 –Fe 1 –Mo 1 –N 3 active sites to boost peroxidase (POD)-like activity. Fe 1 Mo 1 –HC shows a higher substrate affinity ( K m = 0.44 mM for 3,3′,5,5′-tetramethylbenzidine (TMB) and 25.23 mM for H 2 O 2 ) and catalytic efficiency ( k cat / K m = 5.18 × 10 6 M –1 s –1 for TMB and 1.30 × 10 5 M –1 s –1 ) than those of Fe 1 –HC ( K m = 0.82 mM for TMB and 1098 mM for H 2 O 2, k cat / K m = 7.24 × 10 5 M –1 s –1 for TMB, and 7.64 × 10 2 M –1 s –1 ) and Mo 1 –HC ( K m = 0.81 mM for TMB and 647 mM for H 2 O 2 and k cat / K m = 8.60 × 10 5 M –1 s –1 for TMB and 1.49 × 10 3 M –1 s –1 ). Density functional theory investigations reveal that the Fe 1 Mo 1 –HC catalyst has two metal sites, and it overcomes the difficulty in the formation of *O,H 2 O 2 for the single-atom catalysts, resulting in higher POD activity. Based on this property, we constructed a Fe 1 Mo 1 –HC nanozyme sensor for sensitive colorimetric detection of l -penicillamine (L-PA) with satisfactory detection results.