Metallic nanoparticles: from biosynthesis to biomedical applications, current scenarios and prospects

Metallic nanoparticles (MNPs) have attracted significant interest among researchers since the previous century owing to their vast potential applications in emerging fields such as nanotechnology, nano-optics, nanoengineering, nanoenergy, and biomedicine. The rapidly increasing demand for various MNPs has driven researchers to develop facile, inexpensive, scalable, and sustainable synthesis methods to explore their properties and potential for future applications across different scientific and industrial sectors. Due to their intrinsic physicochemical properties, such as surface plasmon resonance, biocompatibility, and luminescence behavior, MNPs have found numerous biomedical applications. Currently, these materials are synthesized and functionalized with different chemical groups, allowing them to conjugate with ligands, antibodies, and drugs of interest. This enables a wide range of applications in biotechnology, targeted drug delivery, magnetic separation, gene and drug delivery vehicles, and importantly, the diagnosis, imaging, and treatment of cancers. Key factors such as size-dependent melting temperature, surface plasmon resonance-based luminescence, and biocompatibility make MNPs highly valuable in bio-industrial applications. Various imaging modalities such as CT, MRI, SERS, ultrasound (US), and other optical imaging techniques have been developed to aid in disease detection and monitoring at various stages. The development of new biomedical techniques and applications requires a comprehensive understanding of the interactions between MNPs and target cells. This review focuses on different types of metallic nanoparticles, their advanced synthesis strategies such as biogenic approaches in addition to conventional methods, and their up-to-date biomedical applications including early detection, diagnosis, imaging, efficient drug delivery, and cancer therapy. Moreover, their antimicrobial activities against harmful bacteria, viruses, and fungi are discussed in detail. In addition, these nanoparticles are highlighted as optical contrast agents for bioimaging techniques such as SERS, MRI, and computed tomography, as well as for use in biosensors to detect biological molecules. Furthermore, by taking advantages of intriguing properties of various metals, biogenically synthesized bimetallic, mixed metal oxides, bifunctional composites, and graphene-based metal composites, can enhance the performance and need to be explored in future for advanced bio medicinal applications.