Eco-friendly carbon nanodots for selective Fe³ ⁺ sensing and antimicrobial activity: A combined experimental–Computational study

Abstract

The sustainable conversion of plant-derived biomass into functional nanomaterials is a central objective in green nanotechnology. In this study, carbon dots (CDs) were synthesized from Evolvulus alsinoides via a single-step, eco-friendly hydrothermal method and comprehensively characterized through combined experimental and computational approaches. High-resolution TEM confirmed monodisperse spherical CDs with an average diameter of ∼5 nm and graphitic lattice fringes ( d -spacing = 0.202 nm). The CDs displayed an excitation-independent blue emission and a pronounced “off–on–off” fluorescence response toward Fe³ ⁺, achieving an ultralow detection limit of 0.015 µM and a linear range of 1.7–360 µM. Cytotoxicity assays demonstrated high cell viability up to 800 µg/mL in A549 cells. At the same time, antibacterial tests revealed a concentration-dependent inhibitory effect against Salmonella enterica Serovar Typhi, with a maximum inhibition zone of 3.033 ± 0.153 cm at 1000 µg/mL. These results highlight the dual potential of the CDs as sensitive Fe³ ⁺ nanosensors and antimicrobial agents. Density Functional Theory (DFT) and COSMO-RS analyses provided atomistic evidence for strong Fe³ ⁺ coordination, significant charge redistribution, and a static fluorescence quenching mechanism arising from ligand–metal complex formation. Overall, this work demonstrates an integrated green-synthesis and modeling framework for producing high-performance, biogenic CDs with applications in environmental monitoring and biomedical diagnostics, contributing to circular-economy valorisation of phytowaste.