Influence of Particle Size and Shapes on the Antifungal Activities of Greener Nanostructured Copper against Penicillium italicum

Pathogenic microorganisms cause diseases that play a limiting role in food production. The growth of blue mold rot on citrus fruits caused by Penicillium italicum poses postharvest economic loss due to food decay. The control of P. italicum using toxic synthetic fungicide raises serious concerns about food safety and quality. There is a need to develop safe fungi management techniques to prevent economic loss in the agro-industry. Copper nanoparticles (CuNPs) are typically prepared at elevated temperatures (200 °C) using toxic surfactants such as cetyltrimethylammonium bromide (CTAB) and harsh organic solvents. We hereby report, for the first time, a novel greener and eco-friendly one-pot aqueous method for synthesizing copper nanospheres (CuNS) and well-defined copper nanocubes (CuNCs) with controlled shape and size using copper­(II) sulfate (CuSO4) precursor and water-soluble quercetin diphosphate (QDP) as a bio-reducing and capping agent at room temperature. The CuNPs were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray diffraction (XRD). CuNCs with average edge lengths of 150–250 and 80–180 nm were designed using QDP and CuSO4 in the ratio of 3:1, respectively. The metrics of sustainability obtained include atom economy (73.56%), molar efficiency (0.9019), and environmental factor (3.429). The antifungal activity of CuNCs and CuNSs was tested against P. italicum using the Kirby–Bauer method. This study demonstrated the comparative effect of CuNCs and CuNSs on the growth of P. italicum spores in a dose-dependent manner. The results indicated that CuNCs and CuNSs showed antifungal activity against the growth of P. italicum, with the minimum inhibitory concentration (MIC) of 100 and 200 μg/mL, respectively. At a constant particle size, it was evident that CuNCs showed significant inhibitory activity of P. italicum at a low-dose treatment (100 μg/mL) in comparison to CuNS. The particle size and shape effect of CuNCs played a vital role in its antifungal activity. QDP-mediated synthesis of CuNC and CuNS could serve as a potent biocide for the natural remediation of citrus-based fungal diseases.