Silver nanoparticle enhanced fluorescence of europium (III) for detection of tetracycline in milk

Metal-enhanced fluorescence (MEF) has shown a promising potential in fluorometric assays. In this work, the fluorescence of europium (Eu3+) was enhanced by silver nanoparticles (AgNPs) through MEF effect in solution phase, which was applied to the detection of tetracycline (Tc). Tc can coordinate with Eu3+ modified on the surface of AgNPs to form EuTc complex, which emits strong fluorescence due to an intramolecular energy transfer from Tc to Eu3+. The MEF effect of AgNPs further enhanced the emission of EuTc complex; the fluorescence of EuTc on the surface of AgNPs was 4 times higher than that of EuTc in a solution phase. The fluorescence intensity of this probe displayed a good linear response to Tc concentrations in the range of 10 nM to 10 μM with a detection limit of 4 nM, and was applied successfully to determine the levels of Tc in milk with a high selectivity. Compared with other fluorescent detection methods for Tc, the presented method allows simple, direct analysis for Tc without requiring fluorescence enhancement reagents or complicated prepreparation processes. This strategy of AgNP-enhanced fluorescence of lanthanide ions could be applicable to improving homogeneous assays of other molecules.