A portable smartphone-assisted fluorescent probe for the visualization and quantitative detection of ferric ions in...

Accurate monitoring of ferric ions (Fe³⁺) in aquatic environments is essential, as elevated concentrations pose serious risks to human health and ecosystems. Herein, a fluorescent sensor based on blue-emissive carbon dots (B-CDs) has been developed for the detection of Fe³⁺ in aqueous solutions. The B-CDs are prepared through a one-step solvothermal method using 5-aminoisophthalic acid and phloroglucinol as precursors and exhibit intense blue fluorescence. Upon the addition of Fe³⁺, the fluorescence of the B-CDs is significantly quenched due to the combined effects of the inner filter effect (IFE) and static quenching mechanism, enabling Fe³⁺ detection with a limit of detection (LOD) of 92 nM over a linear range of 0.092-70 μM. In addition, a smartphone-integrated sensing system is constructed by immobilizing the B-CDs onto filter paper, facilitating on-site visual quantification of Fe³⁺ with a LOD of 176 nM. Furthermore, the sensor exhibits recovery rates ranging from 97.5% to 103.8%, with relative standard deviations (RSDs) below 3.42%. These findings confirm the reliability and high accuracy of the proposed paper-based sensing platform for Fe³⁺ detection in real samples. These results demonstrate that this portable and cost-effective sensing system offers an accurate and practical approach for Fe³⁺ monitoring, with promising applications in health protection and environmental surveillance.