Synthesis and valorization of corn silk-derived carbon dots for antimicrobial fruit preservation

Developing safe and sustainable antimicrobial strategies is critical for postharvest fruit preservation. In this work, corn silk, an abundant agri-food byproduct with a long history of food and medicinal use, was upcycled into fluorescent carbon dots (CS-CDs) via a green hydrothermal route (yield: 27.3%). The resulting CS-CDs were quasi-spherical (∼1.8 nm) and enriched with oxygen-/nitrogen-containing surface groups, exhibiting excitation-dependent blue-green photoluminescence (λ_em ≈ 492 nm at λ_ex = 414 nm). CS-CDs displayed broad-spectrum antibacterial activity against Pseudomonas fluorescens and Staphylococcus aureus, with higher potency against the Gram-negative strain. Mechanistic assays supported a multimodal bactericidal action involving rapid membrane permeabilization (live/dead staining, NPN uptake, and SEM evidence), cytoplasmic leakage, elevated intracellular ROS, and suppressed metabolic activity. CS-CDs also inhibited the postharvest fungal pathogen Penicillium expansum in vitro and reduced decay severity on plums and citrus fruits, as reflected by dose-dependent decreases in lesion area (mm²). When applied as a surface coating (≤1.0 mg/mL), CS-CDs extended the shelf life of jujubes and strawberries by mitigating weight loss and browning, and by lowering microbial loads (CFU/fruit) during storage. Importantly, a practical safety window was supported at functional concentrations, with low cytotoxicity in mammalian cells and no detectable adverse effects on the growth, locomotion, or reproduction of Caenorhabditis elegans. Overall, corn-silk-derived carbon dots provide a promising green antimicrobial platform for postharvest fruit preservation and offer a scalable strategy for valorizing agricultural residues.