A smartphone-integrated test strip platform based on a europium-based ratiometric fluorescent probe for on-site and visual detection of PO43- in milk.

Phosphates are commonly used food additives; however, their excessive use or long-term consumption may pose health risks, making their accurate detection crucial for food safety and human health. In this study, 2-(4-carboxyphenyl)imidazo[4,5-f]-1,10-phenanthroline (HNCP) and pyrazine-2,5-dicarboxylic acid (H2PZDC) were used as ligands to prepare a rare-earth ratio-based fluorescent probe (Eu-NCP-PZDC). This fluorescent probe was successfully applied to the detection of PO43-, demonstrating advantages such as a fast response time (2 min), a low limit of detection (48 nM), a wide linear range (0-320 µM), and good selectivity. Furthermore, by loading this probe onto filter paper and combining it with color recognition software on a smartphone, a fluorescent test strip platform was developed for the visual on-site detection of PO43- in milk, with spiked recovery rates ranging from 97.64% to 105.96% and a relative standard deviation (RSD, n = 6) below 3.28%. Additionally, a hierarchical clustering algorithm was introduced to automatically classify the R/B signals from the test strips, providing an objective and visual means of categorizing the detection data. This work provides a rapid, portable, and simple platform for the detection of PO43- in food samples and holds promising prospects for application in the field of food safety regulation.