Highly luminescent carbon dots (CDs) are obtained from mint leaves adopting a simple and cost effective route devoid of additional chemical reagents and functionalization.

Carbon dots, the celebrated green material among the nanocarbon family, are blessed with several interesting features like biocompatibility, solubility, tunable luminescence, and so forth. Herein, carbon dots derived from Mint leaf extract (M-CDs) via a green method are exploited for versatile applications as a biosensor, reductant, and biomarker. M-CDs are applied for fluorimetric sensing of biologically relevant folic acid through quenching response originating from the inner filter effect, with a limit of detection of 280 nM. The carbon dots were highly selective toward folic acid in a collection of 16 biomolecules. The specificity of carbon dots toward folic acid is explained based on the interaction between the two. Along with sensing, herein, we project M-CDs as a green reducing agent by demonstrating the reduction of Fe(III) and noble metal nanoparticle synthesis from their salt solutions. The particles are found to be significantly non-cytotoxic, as evident from the MTT assay performed on primary H8 cells. The application of M-CDs in multicolor imaging is also illustrated using HeLa cells.

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Herein, a common weed Chromolaena odorata (C. Odorata, Siam weed) is utilized as a precursor for synthesizing carbon dots (CO‐CDs) via a facile hydrothermal method devoid of further functionalization. CO‐CDs possess good water solubility, high photo stability, and intense blue fluorescence with a quantum yield of 2.56 %. Fluorescence of the as‐prepared carbon dots is quenched consequent to interaction with folic acid with high specificity, which enabled its service as an admirable probe for folic acid analysis. The limit of detection (LOD) of folic acid was noted to be 4.5 μM. The mechanism of fluorescence quenching is substantiated through the inner filter effect. The practical utility of the system is assured through analysis of folic acid in commercial samples, with an average range of 90–102 % recovery. Additionally, CO‐CDs are also established to be excellent radical scavengers.