A biosynthesis composite using the green synthesis of titled metal nanoparticles (nickel oxide nanoparticles, NiO NPs, and carbon dots, C-dots) was produced, characterized, and then applied for antimicrobial activities. NiO NPs were produced using the Croton macrostachyus (Bakkannisa) plant leaf extract and nickel nitrate (III) hexahydrate [Ni(NO₃)₂·2H₂O] as precursors, while C-dots were produced using citric acid and o-phenylenediamine (o-OPD). The distribution of the average particle size of the NiO NPs and NiO NPs@C-dots was 25.34 ± 0.12 and 24.95 ± 0.22 nm, respectively. The antimicrobial effects of the prepared materials were tested against the selected bacterial and fungal strains. Based on the outcomes of the bioassay, it was realized that both the bare and composite materials were effective against all bacterial strains. The composite's high surface area with strong inhibitive effective antimicrobial effects against bacterial and fungal strains were observed. Therefore, strong inhibitive effects of 21-24 and 22-26 mm were observed with NiO NPs and NiO NPs@C-dots, respectively.

Carbon dots (CDs) have emerged as a promising class of carbon-based nanomaterials due to their unique properties and versatile applications. Carbon dots (CDs), also known as carbon quantum dots (CQDs) or graphene quantum dots (GQDs), are nanoscale carbon-based materials with dimensions typically less than 10 nanometers. They exhibit intriguing optical, electronic, and chemical properties, making them attractive for a wide range of applications, including sensing, imaging, catalysis, and energy conversion, among many others. Both bottom-up and top-down synthesis approaches are utilized for the synthesis of carbon dots, with each method impacting their physicochemical characteristics. Carbon dots can exhibit diverse structures, including amorphous, crystalline, or hybrid structures, depending on the synthesis method and precursor materials used. CDs have diverse chemical structures with modified oxygen, polymer-based, or amino groups on their surface. These structures influence their optical and electronic properties, such as their photoluminescence, bandgap, and charge carrier mobility, making them tunable for specific applications. Various characterization methods such as HRTEM, XPS, and optical analysis (PL, UV) are used to determine the structure of CDs. CDs are cutting-edge fluorescent nanomaterials with remarkable qualities such as biocompatibility, low toxicity, environmental friendliness, high water solubility, and photostability. They are easily adjustable in terms of their optical properties, making them highly versatile in various fields. CDs find applications in bio-imaging, nanomedicine, drug delivery, solar cells, photocatalysis, electrocatalysis, and other related areas. Carbon dots hold great promise in the field of solar cell technology due to their unique properties, including high photoluminescence, high carbon quantum yield (CQY), and excellent charge separation.