Eco-Friendly Carbon Dots from Pistia stratiotes L.: Development of a Biodegradable Sensor for Selective Detection of Levofloxacin in Water.

Carbon dots (CDs), recognised for their stable and tunable emission properties, have gained momentum as eco-friendly fluorescent probes. This study presents a cost-effective method for synthesising CDs from the aquatic plant Pistia stratiotes L. The morphological, optical and structural analyses of the CDs revealed that they have an average diameter of 2.67 nm and emit strong blue fluorescence with excitation and emission maxima at 375 nm and 455 nm, respectively, alongside an absolute quantum yield of 7.52%. Their surface is rich in hydroxyl, carbonyl, and amino groups, with a negative zeta potential of -16.2 mV. The CDs serve as highly sensitive and selective sensors for detecting the antibiotic levofloxacin (LFN) in water and demonstrate high stability and excellent solubility. The detection mechanism is rapid, with optimal performance at pH 4 and a limit of detection (LOD) of 0.799 μM. A biodegradable polymer composite film (PVA-CA-CDs) incorporating the CDs in polyvinyl alcohol (PVA) matrix was also developed, maintaining strong fluorescence and stability, detecting LFN in micro volumes (20 μL) with an LOD of 7.16 μM. TEM, FE-SEM, and atomic force microscopy (AFM) confirmed uniform dispersion of CDs within the polymer matrix. Validated through analyses of real water samples, recovery values ranged from 95 to 102%, observed for both solution-phase and solid-state sensors. This research is the first to use CDs from Pistia stratiotes L. for LFN detection and introduces an environmentally friendly polymer composite for this purpose.