Biocompatible Cerium Carbonate-Based Nanozymes for Oxidase Activity, Sensing, Computed Tomography Contrast, and Delivery of Small Molecules

Metal carbonate-based nanomaterials have received significant attention in environmental to biomedical applications due to their practical availability, low cost, safety, biocompatibility, and scalability. However, so far, metal carbonate nanostructures are only limited to calcium (Ca), magnesium (Mg), barium (Ba), strontium (Sr), and iron (Fe) carbonates. Moreover, enzyme mimetic activities of direct metal carbonate nanoparticles (NPs) are not yet reported. Given the advantages of metal carbonates, it is highly desired to develop novel metal carbonate nanostructures to address environmental and biological needs. Thus, in the present work, we have developed biocompatible cerium oxycarbonate nanoparticles (Ce₂(CO₃)₂O·H₂O NPs) and systematically studied the enzymatic, computed tomography (CT) contrast and nanocarrier properties. Results reveal that Ce₂(CO₃)₂O·H₂O NPs exhibit enzyme oxidase-like activities by oxidating the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to produce oxidized TMB (ox-TMB) in the absence of hydrogen peroxide (H₂O₂), and it obeys the Michaelis-Menten enzymatic pathway. In addition, Ce₂(CO₃)₂O·H₂O NPs possess good CT contrast properties in a concentration-dependent manner. Moreover, in vitro cellular uptake imaging studies demonstrated the excellent nanocarrier properties of Ce₂(CO₃)₂O·H₂O NPs. Finally, biocompatible studies reveal that the present Ce₂(CO₃)₂O·H₂O NPs are biocompatible and safer for practical applications. Overall, we believed that the present multifunctional properties of Ce₂(CO₃)₂O·H₂O NPs could be a potential candidate in future environmental and biomedical applications.