Sunset yellow (SY) is a widely used food and pharmaceutical colorant, but concerns over its safety highlight the need for sensitive and accurate detection methods. In this work, carbon dots were synthesized from the herbal medicine Honeysuckle (H-CDs). H-CDs exhibited excellent luminescent properties, structural stability, and remarkable selectivity and sensitivity toward SY. This enabled the development of a label-free fluorescent sensor with an ultralow detection limit of 11 nM and a linear detection range of 0-40 μM for SY. The sensor was successfully applied to detect SY in fruit juice samples, yielding recovery rates between 96.1% and 101.0%, demonstrating its practical potential. Additionally, smartphone-assisted SY detection allows convenient real-time, on-site screening. H-CDs also showed low cytotoxicity (cell viability >95% at concentrations up to 2.0 mg/mL), indicating promise for bioimaging and cellular imaging applications. This work presents a sustainable, eco-friendly synthesis of carbon dots with versatile applications in food safety and biological fields.