Sustainable synthesis of metallic nanoparticles and their potential biotechnological applications

Nanotechnology has emerged as a vital interdisciplinary field with applications in medicine, biotechnology, environmental remediation, agriculture, energy, and advanced materials. Metallic nanoparticles (NPs), typically ranging from 1 to 100 nm, have distinctive physicochemical characteristics, including small size, a high surface-area-to-volume ratio, surface reactivity, and tunable electronic properties. Although conventional physical and chemical methods can effectively control nanoparticle (NP) composition and morphology, they may require high energy inputs, specialized equipment, or potentially toxic reagents. Therefore, biological synthesis strategies using plants, microorganisms, and biologically derived molecules have received much attention as alternative approaches for metallic NP synthesis.This review critically evaluates conventional, biological, and hybrid strategies for synthesizing metallic NPS, with particular emphasis on silver (Ag), copper (Cu), and silver-copper (Ag-Cu) bimetallic nanomaterials. The review also discusses NP's characterization methods, including UV-Visible (UV-Vis) spectroscopy, Electron microscopy (EM), X-ray diffraction (XRD), Dynamic light scattering (DLS), zeta-potential analysis, and Fourier-transform infrared spectroscopy (FTIR), while emphasizing the limitations of interpreting any single technique in isolation. This work highlights the transition from laboratory-scale green synthesis to reproducible, scalable nanomanufacturing, including challenges associated with batch-to-batch reproducibility, biological-feedstock variability, purification, process control, safety, toxicity, and life-cycle sustainability. Finally, the review highlights the diverse biotechnological applications of metallic NPs in antimicrobial systems, diagnostics, drug delivery, agriculture, environmental remediation, and related industrial sectors. Overall, the review argues that biological synthesis methods should not automatically be regarded as sustainable. Instead, assess their advantages by integrating material performance, process efficiency, reproducibility, scalability, safety, and environmental impact.