The Use of Capping Agents in the Stabilization and Functionalization of Metallic Nanoparticles for Biomedical Applications

The study of nanoparticles (NPs) and their application in different areas of research, including biomedicine, is attracting the attention of researchers worldwide. Numerous investigations published during the last 20 years cover the fabrication of new materials in the nanoscale, and several uses have been proposed. Metallic nanoparticles (MNPs) have generated a high level of interest, based on improved optical, electrical and magnetic properties, ease of manufacturing, small sizes, and easy functionalization. However, when it comes to Biomedicine, particle aggregation, possible toxicity, and the need for effective cell internalization, still demand active investigation. The main strategy to overcome these drawbacks is possibly the use of capping agents to increase the stability of the particles in dispersion, their biocompatibility and functionalization. In this review, important concepts and characteristics of MNPs, are collected and described. The importance of surface coating for biomedical applications of metallic nanoparticles as well as the most used capping agents and metallic nanomaterials, are also discussed. Finally, the text includes examples and essential characteristics for the biomedical use of MNPs, including the consideration of important challenges. Aspects such as relevant biological activity, increased biocompatibility and functionalization potential are among the most desirable attributes of a capping agent.