A Metal‐Free, Dual‐Mode Colorimetric and Fluorometric Sensing of Rhodamine‐B Using Multifaceted Biogenic Carbon Quantum Dots: A Biocompatible Probe for Biological and Plant Confocal Imaging

ABSTRACT In this study, we present the green synthesis and multifunctional potential of amino‐functionalized carbon quantum dots (ACQDs) derived from Withania somnifera (ashwagandha) for the sensitive detection of Rhodamine B (RhB), a toxic dye commonly found in adulterated food and cosmetic products. The ACQDs exhibited quasi‐spherical morphology with a uniform size distribution (2.82 ± 0.07 nm), abundant surface functional groups (‐OH, ‐COOH, ‐NH₂), and strong photoluminescence. Structural and optical analyses confirmed their excellent stability across a range of environmental conditions, including pH, UV exposure, and saline media. A dual‐mode sensing of RhB was achieved via visible colorimetric change and fluorescence quenching, with a low quantification limit (LOQ) of 1.9 μgL −1 . Mechanistic studies revealed that both static and dynamic quenching, involving electrostatic interactions, hydrogen bonding, and π–π stacking, contributed to the sensing process. The ACQDs also demonstrated notable antioxidant activity (IC50 = 0.168 mg mL −1 ) and low cytotoxicity (< 90 μg mL −1 ) in NIH‐3 T3 cells, confirming their biocompatibility. Furthermore, their efficient internalization into plant tissues highlights their suitability for plant imaging. These results establish ACQDs as a promising nanomaterial for applications in environmental monitoring, food safety, biomedical diagnostics, and agricultural research.