Highly Catalytic Palladium Nanoclusters and Pd-Enzyme Composites as Catalytic Cascade Systems for Biosensing^†

Ultrasmall palladium nanoclusters have garnered significant attention due to their exceptional catalytic performance. However, their high surface energy always leads to aggregation, reducing the number of active sites and thereby decreasing catalytic efficiency. Herein, a molecular cage (RCC3) was utilized as a confined environment to stabilize ultrasmall PdNCs. The excellent solubility and open framework of cages not only enhance the solubility of palladium nanoclusters but also significantly improve their catalytic activity and stability. The prepared palladium nanoclusters were found to exhibit both peroxidase-like and oxidase-like activities. Under acidic conditions, the protonation of the molecular cage framework facilitates the assembly of ionic Pd nanoclusters with negatively charged enzymes through electrostatic interactions, forming a cascade system. The system is capable of detecting substrates, such as glucose and ascorbic acid, providing a highly catalytic platform for biosensing applications.