Synthesis and DFT calculation of microbe-supported Pd nanocomposites with oxidase-like activity for sensitive detection of nitrite

Nanozymes have emerged as the forefront of research in analytical sensing due to their promising applications. In this study, we utilized polyethyleneimine (PEI)-modified Pichia pastoris residue to synthesize microbial-based palladium nanocomposites (Pd/MMR) through simple in-situ reduction methods. The dispersed active sites of Pd nanoparticles with a size of 2.12 +/- 0.49 nm that were supported by microbial biomass provided excellent oxidative enzyme-mimicking activity to Pd/MMR. The catalytic mechanism of Pd/MMR involved the combined action of O-1(2), center dot OH, and center dot O-2(-), and possible reaction pathways and corresponding energy barriers were also revealed using DFT calculations. We also established a quantitative detection platform for nitrite using Pd/MMR. The platform could detect nitrite at concentrations of 10-300 mu M with a detection limit of 0.27 mu M, and was successfully applied to detect nitrite in real samples. These findings serve as a reference for the synthesis and application of metal nanocomposites using microorganisms.