Ethylenediamine-assisted synthesis of a highly active manganese-based nanozyme for total antioxidant capacity...

Manganese-based nanozymes have shown great potential in sensor construction. However, building manganese-based nanozymes with high oxidase-like activity under mild preparation conditions remains challenging. Herein, for the first time it has been proposed a simple strategy using ethylenediamine to synthesize a amorphous/crystalline hetero-phase nanozyme (B-MnO_x-EDA) by avoiding harsh conditions. Additionally, boron was indeed doped into manganese-based metal oxides form boron-doped manganese nanozymes (B-MnO_x-EDA) which enhanced oxidase-like activity. Experimental results demonstrated that B-MnO_x-EDA nanozymes exhibit strong affinity for TMB (K_m = 0.033 mM), high catalytic activity (V_max = 31.5 × 10^-7 M s^-1), and the ability to avoid using hydrogen peroxide, thereby advancing nanozyme sensing capabilities. The B-MnO_x-EDA nanozymes were effective under a wide range of pH, temperature, and electrolyte conditions, and exhibited long-term stability, making them suitable for applied biosensing. Additionally, the B-MnO_x-EDA nanomaterials were assembled onto Whatman filter paper (WFP) to prepare paper chip (B-MnO_x-EDA@WFP). Under optimal conditions, we established ultraviolet and visible (UV-vis) spectrophotometric and smartphone-based paper chip colorimetric methods to evaluate the total antioxidant capacity of traditional Chinese medicine based on the absorbance signal of the solution and the color change of the paper-based chip, respectively. The detection results of actual samples were consistent with those of commercial assay kits. Moreover, compared to the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) assay method, B-MnO_x-EDA nanozymes showed significant advantages in detecting thiol-containing substances. This work not only provides a strategy for developing highly active manganese-based nanozymes with mild preparation conditions but also demonstrates their potential for rapid antioxidant evaluation in traditional Chinese medicine.