Smartphone-assisted fluorescent sensor for the visualization and quantitative detection of doxycycline and L-arginine

A novel smartphone-assisted fluorescent sensor based on europium/zirconium metal-organic framework (Eu_0.5/Zr_0.5-MOF) was developed for the fast and sensitive determination of doxycycline (DOX) and L-arginine (Arg). After the addition of DOX, the fluorescence of Eu_0.5/Zr_0.5-MOF was quenched owing to the inner filter effect (IFE). When Arg was introduced into the Eu_0.5/Zr_0.5-MOF@DOX complex system, the fluorescence was recovered because the interaction between Arg and Eu_0.5/Zr_0.5-MOF@DOX weakened the IFE. Moreover, the Eu_0.5/Zr_0.5-MOF produced continuous fluorescence color changes for the visual measurement of DOX and Arg. The fluorescent probe for DOX and Arg offered broad linear ranges of 0.05-80 and 0.1-60 μg/mL, respectively, with detection limits as low as 2.07 and 67.5 ng/mL. The proposed method was successfully applied to monitor DOX in eggs and Arg in human serum. This work provides a powerful platform for the real-time and visual analysis of DOX and Arg in food and biological samples.