Antimicrobial resistance (AMR) is one of the most significant global health threats of the 21st century, driving the urgent search for alternatives to conventional antibiotics. Copper nanoparticles (CuNPs) have gained attention due to their broad antimicrobial spectrum, cost-effectiveness, and versatile applications in medicine, agriculture, and the food industry. This review provides a systematic overview of the advances in CuNP synthesis, mechanisms of antimicrobial action, biomedical and industrial applications, and associated toxicity issues. A comprehensive literature review was conducted, covering chemical, physical, and biological synthesis strategies; mechanistic studies on microbial inhibition; and experimental reports on biomedical and environmental applications. A comparative analysis revealed opportunities, limitations, and knowledge gaps, with particular emphasis on cytotoxic and ecotoxicological aspects. CuNPs show strong antimicrobial activity against bacteria, fungi, viruses, and multidrug-resistant strains through mechanisms such as reactive oxygen species (ROS) generation, membrane disruption, and DNA/protein interactions. Their use in medical devices, wound dressings, textiles, and packaging materials underlines their application potential. However, cytotoxicity to mammalian cells, ecological risks, and the lack of standardized safety protocols remain critical challenges. Particle size, morphology, and surface chemistry strongly influence both efficacy and toxicity, underlining the importance of controlled synthesis and functionalization. Overall, CuNPs represent a promising strategy to tackle the AMR crisis. Future research should focus on environmentally friendly and surface-modified synthesis approaches, standardized toxicity assessments, and robust regulatory frameworks. By balancing antimicrobial efficacy with biosafety and sustainability, CuNPs could become a transformative platform for clinical, industrial, and environmental applications.

Silver nanoparticles (AgNPs) have attracted considerable attention due to their outstanding catalytic and antimicrobial properties. Nevertheless, most aqueous syntheses yield colloids with low metal concentrations and limited long-term stability, restricting their practical use. To address these challenges, highly concentrated and stable AgNP dispersions were prepared, reaching concentrations of up to 100 mM, by chemical reduction of AgBF4 with tetrabutylammonium borohydride in the presence of polyvinylpyrrolidone (PVP) as a stabilizer. The dispersions contained predominantly spherical nanoparticles with narrow size distributions and remained stable for at least 1 month. For improved reusability, the AgNPs were incorporated into regenerated cellulose films produced in 1-butyl-3-methylimidazolium chloride. Owing to its abundance, renewability, and biocompatibility, cellulose provides a sustainable and environmentally friendly platform for supporting metal nanoparticles, offering easy handling and potential for reuse. The resulting AgNP-cellulose composites contained up to 5 wt % of silver and preserved the cellulose type II structure. Structural, thermal, and morphological analyses confirmed the homogeneous distribution of PVP-stabilized AgNPs within the matrix. The hybrid films exhibited high catalytic activity toward 4-nitrophenol reduction and could be reused for at least five consecutive cycles with minimal loss of performance. In addition, antibacterial assays against Escherichia coli (ATCC 8739) and Staphylococcus aureus (ATCC 25923) showed antibacterial activity, with a statistically supported and concentration-dependent response that was more pronounced for the Gram-positive strain. This work demonstrates a straightforward strategy to combine concentrated AgNP dispersions and cellulose supports, yielding recyclable catalytic and antimicrobial materials.