Unveiling the Biosynthesis Pathways of PdAu Nanoparticles Mediated by Cellular Oxidoreductases and Extracellular Polymeric Substances

Biogenic PdAu nanoparticles (bio-PdAu NPs) synthesized by microorganisms exhibit remarkable catalytic activity relevant to environmental remediation. This study investigates the biosynthetic pathway of bio-PdAu NPs synthesized by Shewanella oneidensis MR-1, revealing that the bioreduction of Pd(II) and Au(III) follows first-order kinetics. Inhibition of NADH dehydrogenase (rotenone, Rot-PdAu), c-Cyts (diuron, Diu-PdAu), and hydrogenase (Cu2+, Cu-PdAu) decreased total metal-ion reduction efficiencies and Pd/Au composition, in which hydrogenases contributed most, followed by NADH dehydrogenase and c-Cyts. Notably, the presence of inhibitors affected the Au(III) reduction efficiency, altering particle size and composition. Statistical analysis indicated average particle sizes of 45.45, 50.15, and 13.16 nm for Rot-PdAu, Diu-PdAu, and Cu-PdAu, respectively, with a positive correlation to kinetic constants (R2 = 0.82). During biosynthesis, intracellular and extracellular pathways contributed 76.55 and 23.44%, respectively. For electrocatalytic hydrogen evolution reaction, the maximum current density (jmax) of bio-PdAu NPs exhibits substantially superior electrocatalytic performance compared to monometallic counterparts, with current densities approximately 1.8–3.2 times higher than individual bio-Pd or bio-Au systems. These findings deepen the understanding of the controlled synthesis pathways of bio-PdAu NPs and offer insights for developing biobimetallic NPs for environmental applications.