A convenient tool for real-time detection of iron content in human food

Abstract

A fluorescent sensor, (E)-2-(((5-(5-methoxy-1H-benzo[d]imidazol-2-yl)thiophen-2-yl)methylene)amino)phenol (OMTP), was designed for direct application onto the surface of onions for real-time monitoring of iron content using a smartphone. The probe OMTP exhibited weak fluorescence in EtOH/H₂O (49 : 1) because of its non-planar molecular configuration, but showed a strong green emission at 530 nm after coordination with Fe^3+/2+. The probe displayed high sensitivity, with a detection limit as low as 0.014 µmol L⁻¹, enabling trace-level iron analysis. Theoretical calculations showed that Fe^3+/2+ coordination reduced the activation barrier for CN bond cleavage of the probe OMTP from 234.12 to 35.51 kJ mol⁻¹, promoting hydrolysis and fluorescence recovery. In addition to its excellent sensing performance, OMTP demonstrated practical applicability in multiple food and agricultural scenarios, including real-time monitoring of iron absorption during the growth of onions and bean sprouts, rapid determination of iron in beverages such as wine using test strips, and visual detection of iron on the surfaces of fruits and vegetables. Notably, the portable sensing platform allows non-professionals to perform on-site and household self-inspection of dietary iron intake. It has significant potential for application in the fields of food and agriculture.