Galvanic Replacement-Driven Structural Evolution of Pd–Pt Alloy Nanoflowers with Modulated d-Band Center for Electrochemiluminescence Biosensing of Organophosphates

Organophosphorus pesticides (OPs) are widely used agrochemicals that pose health risks through irreversible acetylcholinesterase (AChE) inhibition, necessitating reliable detection. Herein, we report an electrochemiluminescence (ECL) biosensor based on Pd–Pt nanoflowers (Pd–Pt NFs) for diazinon detection, powered by oxygen reduction reaction (ORR). Driven by galvanic replacement, cubic Pd templates evolve into Pd@Pt nanodendrites and finally fully alloyed Pd–Pt NFs. Benefiting from the nanoflower geometry and the ligand effect-modulated Pt d-band center, the catalyst delivers exceptional ORR activity. On this basis, an ORR-mediated ECL signal transduction strategy is proposed. Diazinon inhibits AChE, reducing thiocholine (TCh) generation from acetylthiocholine (ATCh); the thiol-bearing TCh selectively poisons ORR-active sites of Pd–Pt NFs, quenching the ECL signal in a concentration-dependent manner. Experimental and theoretical results verify the strong TCh adsorption affinity on the Pd–Pt alloy surface. The biosensor achieves a detection limit of 2.7 pg mL–1 toward diazinon, alongside favorable selectivity, reproducibility, and reliable recoveries in real samples. Moreover, the platform was extended to flexible hydrogel-integrated electrodes for in situ cleaning and degradation monitoring. This work demonstrates that galvanic replacement-tuned Pd–Pt NFs, coupling ORR catalysis with coreactant-free ECL, offer a versatile strategy for OPs biosensing.