Eu3+-ion doped strontium molybdate perovskite quantum dots as a turn-off-on fluorescent sensor for simultaneous detection of hypoxanthine biomarker and Fe3+ ions

A fluorescence “turn-off-on” nanoprobe is designed by using europium-doped strontium molybdate perovskite quantum dots (Eu³⁺:SMO PQDs) for the sequential detection of hypoxanthine (Hx) and Fe³⁺. The Eu³⁺:SMO PQDs were prepared by the sol-gel method using Sr(NO₃)₂, (NH₄)₆Mo₇O₂₄.4H₂O, and Eu(OCOCH₃)₃ as precursors. The green fluorescence of Eu³⁺:SMO PQDs was efficiently reduced (turn-off) in the presence of Hx, then it was restored (turn-on) gradually by introducing Fe³⁺ due to the competitive formation of Hx@Fe³⁺, which results to the release of Eu³⁺:SMO PQDs. In addition, the fluorescent probe exhibits excellent selectivity and sensitivity. Under the optimized experimental conditions, linear ranges and detection limits were 0.25–25 μM and 12.30 nM for Hx and 0.025–50 μM and 10.44 nM for Fe³⁺ , respectively. Furthermore, the fluorescence method was successfully explored to detect Hx and Fe³⁺ in plasma and urine samples.