A fluorescent probe based on the interaction of ofloxacin with gold nanoparticles for the sensitive detection of melamine†

Melamine (MEL) is frequently adulterated in dairy products to manipulate protein content test results due to its high nitrogen content. In this study, a fluorescent probe based on ofloxacin (OFL) and gold nanoparticles (AuNPs) was proposed for the specific and sensitive detection of MEL. In the pH range of 4.5–7.5, the fluorescence spectrum of OFL exhibits a high degree of overlap with the absorption spectrum of AuNPs, and interactions based on fluorescence resonance energy transfer (FRET) occur, with significant quenching of OFL fluorescence accompanied by a change in fluorescence lifetime. After being incorporated into MEL, the amino group of MEL specifically interacted with the surface of AuNPs through coordination. This interaction triggered the aggregation of AuNPs, which in turn led to the fluorescence recovery of OFL. The detection of melamine was accomplished by quantifying the change in fluorescence intensity of OFL. Under optimized conditions, the MEL concentration exhibited a strong linear relationship with the relative fluorescence intensity of the probe (R² = 0.994) within a range of 0.1 to 1.6 μM. The limit of detection was determined to be 7.28 nM. It is noteworthy that the method was validated in real milk samples, with recovery rates ranging from 98.2% to 107.1%. The method exhibits excellent selectivity and sensitivity for MEL, making it a suitable tool for the environmental detection of milk.