Dual-functional Rh6g@Eu-DDB as a fluorescence-enhanced ratiometric sensor for norfloxacin and a fluorescence turn-off sensor for nitrofurantoin in water and food samples

Abstract

The detections of norfloxacin (NFX) and nitrofurantoin (NFT) are of significance due to their threat to human health resulting from their excessive use. A MOF-based composite of Rh6G@Eu-DDB was prepared through a one-pot synthesis of Eu(NO₃)₃·6H₂O with 1,3-di(3′,5′-dicarboxylphenyl)benzene (H₄DDB) in the presence of rhodamine 6G (Rh6G). Rh6G@Eu-DDB acted as a fluorescence-enhanced ratiometric sensor for NFX and a fluorescence turn-off sensor for NFT. The sensitivity test of Rh6G@Eu-DDB for sensing NFX revealed a linear fitting equation of I₆₁₃/I₅₅₄ = 0.0642C_NFX + 3.4103 (I₅₅₄ and I₆₁₃ = the emission intensities at 554 and 613 nm and C_NFX = NFX concentration) with a limit of detection (LOD) = 69.71 nmol L⁻¹ (nM). NFT detection gave a linear fitting equation of (I₀ − I)/I = 0.0126C_NFT (C_NFT = NFT concentration) with a LOD of 0.85 µM. The fluorescence assays using Rh6G@Eu-DDB were applied in water and milk for NFX and in egg and honey for NFT, whose measured concentrations were close to the spiked concentrations and their fluorescence recoveries were around 100% with all relative standard deviations of less than 3%. These findings support that the presented fluorescence assays are reliable and accurate. The smartphone-assisted method contributes to the visualization of NFX and NFT detections through the green/red values vs. concentration. This study provides a facile solution for antibiotic detection.