Using ratiometric indicator-displacement-assay in semi-quantitative colorimetric determination of tetracyclines

In this work, a novel colorimetric sensor array based on ratiometric indicator-displacement assay has been developed for the recognition and semi-quantitative detection of tetracycline, oxytetracycline, chlortetracycline, and doxycycline. The sensor array was fabricated by various combinations of 5 indicators and 3 metal cations. Based on the difference of complex stability constant, the competitive binding between metal cations with tetracyclines and indicators resulted in different color recovery of indicators through indicator-displacement reaction. By adjusting the concentrations of metal cations, the discrimination of tetracyclines has been achieved on as-fabricated sensor array and the lowest concentration for discrimination of tetracyclines could be 1 μmol/L, which was similar to those sensor arrays based on fluorescent nanomaterials. Meanwhile, the color difference between tetracyclines has been further enlarged by color overlaying of complexes of tetracyclines and metal cations, which enriched the distinguish capability of the sensor array and promised the discrimination ability for tetracyclines with various concentrations. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) demonstrated that the colorimetric sensor array has an excellent capability to discriminate tetracyclines at different concentrations from potential interferants. The detection range for tetracyclines was 1–50 μmol/L and the limit of recognition for tetracyclines was 1 μmol/L with the colorimetric sensor array. Finally, this colorimetric sensor array was successfully applied for tetracyclines differentiation in real samples.