Component-tunable PdRh Bimetallic Nanozyme for Ultra-sensitive Colorimetric Detection of Nitrite

A series of bimetallic nanozymes(Pd3Rh, PdRh, PdRh3) was prepared using one-pot hydrothermal method by adjusting the ratio of palladium(Pd) to rhodium(Rh). The peroxidase-like(POD-like) and oxidase-like (OXD-like ) activities of nanozymes were tested. The results showed that the catalytic activity of bimetallic nanozymes was significantly enhanced compared to that of single metallic nanozymes(Pd, Rh). The POD-like and OXD-like activities exhibited obvious component dependence, and PdRh3 and PdRh nanozyme showed the strongest POD-like and OXD-like activity, respectively. The analysis of enzymatic kinetics showed that the Michaelis-Menten constant (K m ) of PdRh3 nanozyme with 3,3',5,5'-tetramethylbenzidine(TMB) and H2O2 as substrates are 15.65 and 381.99 mu mol/L, respectively. The corresponding maximum velocity(vmax) reach 8.40x10-8 and 11.01x10-8 mol/(L<middle dot>s). In addition, the POD-like activity of PdRh3 nanozyme was pH-dependent , and the optimized activity was obtained at pH=5. A colorimetric sensing system was developed based on PdRh3 nanozyme, which realized the rapid quantitative detection of nitrite concentration in solution according to the fitting relationship between the absorbance ratio(A445 nm/ A 652nm ) and the concentration of nitrite ion(NO2-). The limit of detection(LOD) in pH=5 buffer and pure water are 0.467 and 30.523 mu mol/L, respectively, and the system has a good specificity under the interference of various salt ions, demonstrating great application potential in biosensing.