Highly stable and biocompatible zwitterionic dendrimer-encapsulated palladium nanoparticles that maintain their catalytic activity in bacterial solution

Abstract

The development of artificial enzymes to mimic the properties of natural enzymes has been receiving much research interest. Herein, zwitterionic dendrimer-encapsulated palladium nanoparticles (Pd_n-G5MC NPs) were constructed to investigate their biocompatibility and catalytic ability in bacterial solution. Zwitterionic dendrimer templates were synthesized via the surface modification of generation 5 polyamidoamine (G5 PAMAM) dendrimers with maleic anhydride and cysteamine. The Pd_n-G5MC NPs were prepared by incubation of the templates with disodium tetrachloropalladate, followed by reduction with sodium borohydride. The Pd_n-G5MC NPs displayed high stability, biocompatibility, and catalytic efficiency. Remarkably, Pd₅₅-G5MC NPs maintained high stability over a broad pH range (4–9) and high salt concentration (up to 20%) within 24 h. Pd₅₅-G5MC NPs did not show noticeable cytotoxicity to HUVEC cells or HeLa cells at a concentration of 500 μg mL⁻¹, while G5 PAMAM dendrimer-encapsulated palladium nanoparticles (Pd₅₅-G5 NPs) had obvious cytotoxicity (∼10% cell viability). Furthermore, Pd₅₅-G5 NPs had a minimal inhibitory concentration (MIC) of 400 μg mL⁻¹, while Pd_n-G5MC NPs did not show any bacterial growth inhibition at the same concentration. More importantly, Pd₅₅-G5MC NPs maintained their catalytic activity in bacterial solution compared to Pd₅₅-G5 NPs. The apparent rate constant k_app is dependent on the concentration of morin or hydrogen peroxide. All the forementioned properties suggested that Pd_n-G5MC NPs could be employed in bio-related systems in nature.