Senna-based carbon quantum dots as probes for the determination of Fe3+ and dopamine

Carbon quantum dots (CQDs) are widely used in optical biosensors due to their good biocompatibility and easy synthesis type. Although the carbon sources for preparing CQDs are quite extensive, it is not common to prepare CQDs using herbs as carbon sources. Therefore, CQDs for fluorescence determination of Fe³⁺ and dopamine (DA) were prepared by microwave heating using senna leaf as carbon source. The prepared CQDs showed good dispersion and uniform sphericity under transmission electron microscopy (TEM), with an average particle size of 3.510 nm. Under ultraviolet light, CQDs fluoresce brightly blue and have a strong fluorescence (>1.200*10³ a.u.), with no change in fluorescence intensity over a week. The prepared CQDs were quenched by Fe³⁺ and DA probably due to the static burst effect, which can be confirmed by X-ray photoelectron spectroscopy (XPS) and fourier-transform infrared spectroscopy (FT-IR) analyses. The method has a good linear relationship for Fe³⁺ in the range of 10–3000 μmol/L with a determination limit of 0.1671 μmol/L, and an excellent linear relationship for DA in the range of 5–3000 μmol/L with a determination limit of 0.1653 μmol/L. The method was applied to the determination of Fe³⁺ and DA in real samples, and the recovery rate was satisfactory.