Ultra-selective pyrene-based fluorescent sensor for detection of Fe+3 in neat aqueous medium

Transition metals, particularly Fe+3, play vital roles in biological and environmental systems, yet their chronic elevation can lead to severe diseases. Early detection of Fe+3 is crucial for diagnosing associated ailments. While traditional detection methods have drawbacks, fluorescent sensors offer promising alternatives due to their ease of use, cost-effectiveness, and real-time monitoring capability. Pyrene-based sensors have demonstrated notable sensitivity and selectivity for Fe+3, but challenges remain in achieving applicability in neat aqueous systems. We present two novel turn-off pyrene-based sensors, APTS (sodium 8-aminopyrene-1,3,6-trisulfonate) and APSS (sodium (E)-4-hydroxy-3-((pyren-1-ylimino)methyl)benzenesulfonate), incorporating sulfonate groups to enable their use in pure water samples and achieve nanomolar-level detection limits. Through meticulous experimental and characterization efforts, we elucidate the significance of the imine linkage in enhancing selectivity towards Fe+3 ions. Our sensors exhibit exceptional selectivity and sensitivity, with LODs of 45.6 nM and 45.9 nM for APTS and APSS, respectively, surpassing environmental protection guidelines. Additionally, binding stoichiometry studies reveal insights into the interaction mechanisms, supported by fluorescence lifetime analysis and DFT studies. APSS particularly stands out for its lack of interference from other metal ions, notably Cu2+ as well as Fe2+, offering promising potential for real-time applications and development of paper strip tests. The practical applicability of our sensors is demonstrated through successful Fe+3 detection in various water samples with recoveries ranging from 94 % to 104 %. Overall, our study highlights the effectiveness of APTS and APSS as robust fluorescent probes, with implications for environmental monitoring and biomedical diagnostics.