Bioactive Amino-Carbon Dots for Sustainable Crop Protection: Cellular Uptake and Metabolomic Insights into the Antifungal and Antibacterial Activity in Tomato Plants

Amino-functionalized carbon dots (CDs-NH₂) are emerging as multifunctional nanomaterials for sustainable agriculture due to their tunable surface chemistry, water dispersibility, low toxicity, and inherent antimicrobial activity. In this study, we envisioned the application of CDs-NH₂ as both antifungal and antibacterial materials against plant pathogens, thoroughly assessing CDs-NH₂ internalization and their effects on plant growth and metabolomic profiles as well as defense responses to pathogen infection. Initially, CDs-NH₂ were synthesized and fully characterized with a focus on morphology, structure, and their stability under biotic and abiotic environmental conditions. Antioxidant assays based on DPPH and ABTS radical scavenging demonstrated the redox activity of CDs-NH₂. Fluorescence microscopy investigations demonstrated that CDs-NH₂ can quickly penetrate plant and fungal cells. Confocal microscopy investigations, complemented by colocalization studies with endocytic tracer FM4-64, demonstrated that endocytosis is the primary mechanism for CDs-NH₂ cellular uptake in Botrytis cinerea. Furthermore, CDs-NH₂ were found to quickly penetrate plant cells, enhancing tomato seed germination and subsequent development. Quantitative chemical analyses indicated the absorption of CDs-NH₂ via the root system of the rice seedlings. In vitro and in planta experiments have shown the efficacy of CDs-NH₂ against phytopathogenic fungi (Botrytis cinerea) and bacteria (Pseudomonas syringae pv. tomato). In vitro antibacterial activity tests combined with metabolomic analyses via ¹H NMR indicate that CDs-NH₂ exert their antimicrobial activity straight on P. syringae and trigger defense responses in the plant upon infection. Overall, these findings highlight the dual role of CDs-NH₂ as antivirulence agents and metabolic modulators, underscoring their potential as sustainable nanotools for integrated crop protection at the plant-pathogen interface while emphasizing the need for further investigation into their environmental and human safety.