A Novel Universal Naked-Eye Fluorescent Sensor for Fe3+ Detection in Fertilizer Water, Dietary Supplements, and Living Cells

The global trend toward health consciousness has led many people to focus on wellness and nutrition, driving the rapid growth of dietary supplements. Fe 3+ is one of the most common ingredients used to support individuals at risk of Fe deficiency. It is also used in the form of fertilizers to improve crop yield. However, the deficiency and excess of iron can be harmful to the human health and plants. Therefore, reliable methods for qualitative and quantitative iron detection must be developed. This study successfully synthesized a new sensor ( Rox ) using rhodamine B, which serves as a fluorescent dye and an ion-binding site. In addition, an oxime group was incorporated into the structure to improve its hydrophilic properties. Rox exhibited excellent sensitivity and selectivity toward Fe 3+ over other competing metal ions and operated through a turn-on fluorescence mechanism. The sensor exhibited a rapid response: it detected Fe 3+ within 1 min with a detection limit of 3.54 ppb. Moreover, Fe 3+ could be visually detected by the naked eye through a distinct color change from colorless to pink in a CH 3 CN:H 2 O (3:7, v/v) solvent system. Rox demonstrated promising performance in detecting Fe 3+ in various water samples and living cells. It shows potential for application in portable paper-based qualitative assays. Thus, this study presents a straightforward approach for iron detection in fertilizer samples and pharmaceutical products, enabling safety and quality control and contributing to progress toward the United Nations Sustainable Development Goals. • A novel naked-eye rhodamine-based fluorescent sensor ( Rox ) exhibits enhanced fluorescence in the presence of Fe 3+ , with high sensitivity, a low limit of detection, and a rapid response. • The detection limit of Rox for Fe 3+ is 3.54 ppb. • Rox -coated test strips were fabricated for visual Fe 3+ detection. • Rox was used to trace Fe 3+ in fertilizer water, dietary supplements, and living cells. • Rox is the first fluorescent sensor enabling naked-eye recognition of Fe 3+ in various fertilizers under both ambient and UV light.