Mild synthesis of biomass-derived fluorescent Fe,N-carbon dots for fluorometric and smartphone-assisted visual detection of aloin.

Herein, a mild one-pot synthesis of fluorescent Fe,N-doped carbon dots (Fe-NCDs) was developed from biomass waste in a choline chloride/urea deep eutectic solvent (DES) with FeCl3 as a promoter. The DES disrupts the lignocellulosic network while FeCl3 catalyzes carbonization and provides in situ Fe doping. The resulting Fe-NCDs exhibited bright blue emission with a high quantum yield of 38.5% owing to the introduction of Fe and N elements. The probe showed outstanding environmental stability but could be selectively fluorescence quenched toward aloin because of static coordination and the inner filter effect. Thus, it was used for the fluorescent sensing of aloin with a linear response between 0.5-200 μM and a LOD of 0.043 μM. The practical utility of the sensor was validated by quantifying aloin in real bovine serum and commercial aloe-based products. Furthermore, a smartphone-assisted visual detection platform was established using the Fe-NCD probe for rapid semi-quantitative aloin analysis via RGB color extraction. This work demonstrates a low-temperature, energy-sustainable waste-to-sensor strategy for producing high-performance Fe,N-carbon dots and validates their utility in smartphone-based visual aloin detection for quality control of aloe products.