Upconversion luminescence nanosensor for detection of Fe³⁺ and phosphate ion based on the inner-filter effect

In this work, an upconversion luminescence (UCL) nanosensor for fast detection of ferric ion (Fe³⁺) and phosphate ion (Pi) is developed based on the inner-filter effect (IFE) between NaYF₄:Yb/Er upconversion nanoparticles (UCNPs) and Fe³⁺-hypocrellin B (HB) complex. Fe³⁺-HB complex has strong absorption band (450-650 nm), which overlaps with the green emission peak of UCNPs at 545 nm. By adding Fe³⁺ and Pi, the UCNPs-HB system produces the red-shift change of absorption spectrum, which leads to the "on-off-on" process of IFE. So, with the specific recognition ability of HB for Fe³⁺ and the competitive complexation of Pi for Fe³⁺, the proposed nanosensor utilizes the UCL change to achieve the detection of the targets. For the detections of Fe³⁺, the linear range is 10-600 μM with a limit of detection (LOD) of 2.62 μM, and for Pi, the linear range is 5-100 μM with a LOD of 1.25 μM. The results for selectivity, precision, and recovery test are also satisfactory. Furthermore, the real sample detection shows that the proposed nanaosensor has a great potential in environmental and biological systems. An upconversion luminescence (UCL) nanosensor based on the inner-filter effect (IFE) between upconversion nanoparticles (UCNPs) and Fe³⁺-hypocrellin B (HB) complex for the detection of Fe³⁺ and phosphate ion has been proposed, which is promising to be a convenient and sensitive assay for monitoring Fe³⁺ and phosphate ion in different environments and biological systems.