Quantitative On-Site Instrument-Free Visual Detection of Ferric Ions in Environmental and Biological Samples Using a Novel Fluorescent Metal–Organic Framework

This study presents a novel approach for the on-site quantitative visual detection probe of ferric ions (Fe³⁺) in real samples using a fluorescent zinc-based metal–organic frameworks (denoted as UoZ-8). The novel UoZ-8 produces strong blue emission at 390 nm when excited at 330 nm. The UoZ-8-based probe utilizes the unique fluorescent properties of MOFs when it quenches in the presence of Fe³⁺ ions via inner filter effect. By exploiting the high sensitivity and selectivity of these MOFs, the probe provides a simple, instrument-free, cost-effective, and reliable method for Fe³⁺ detection. On–Off mode was used for detection of Fe³⁺ ions using conventional fluorometry and smartphone assisted visual detection. By analyzing the blue intensity changes of blue channels with the assistance of smartphone, the quantitative detection was realized within the range of 10.0–125.0 µM with limit of detection 0.23 µM. Real water sample analyses validate the effectiveness of the probe in various matrices, showing its potential for environmental monitoring and industrial applications. The results highlight the ability of MOF to deliver accurate and rapid measurements, making it a valuable tool for on-site ferric ion detection.