A rhodamine coumarin-derived fluorescence probe that selectively detects Fe³⁺ and measures radiation doses

We synthesized a fluorescence ratiometric probe by combining coumarin and rhodamine B with ethylenediamine to sense Fe³⁺ and measure ionizing radiation doses. The presence of Fe³⁺ caused rhodamine to transition from a closed helical structure to an open-ring structure. Additionally, fluorescence resonance energy transfer (FRET) occurred between coumarin and rhodamine B. As a result, the fluorescence intensity at 405 nm (I₄₀₅) due to coumarin was decreased, whereas that at 585 nm (I₅₈₅) derived from open-ring structure rhodamine B was increased. The ratio of I₅₈₅ and I₄₀₅ (I₅₈₅/I₄₀₅) linearly increased as the Fe³⁺ concentration increased. The probe sensed Fe³⁺ in a 0-110 μM range, with a lower limit of detection (LOD) of 0.226 μM. Inspired by Fricke dosimeters, we extended the probe to measure X-ray doses using the fluorescence methodology. The probe measured X-ray doses in a 0-30 Gy range with a lower LOD of 0.5 Gy. Additionally, the dosing capability was independent of the dosing rates. Our probe showed potential for detecting Fe³⁺ and measuring ionizing radiation doses.