Tandem Förster resonance energy transfer induced visual ratiometric fluorescence sensing of tetracyclines based on zeolitic imidazolate framework-8 incorporated with carbon dots and safranine T.

Developing new methods for efficiently detecting tetracycline antibiotics in water has gained much importance. In this work, zeolitic imidazolate framework-8 (ZIF-8) was used as a host to encapsulate carbon dots (CDs) and safranine T (ST) during its self-assembly process to synthesize CDs/ST@ZIF-8, which was then applied as the dual-emissive probe for detecting tetracycline antibiotics. Benefiting from the confinement effects of ZIF-8 and its fluorescence enhancement effects toward tetracycline (TC), a unique tandem Förster resonance energy transfer (FRET) system from CDs to TC and then to ST could be established, with a low limit of detection of 46 nM and excellent selectivity. More importantly, as compared to the CDs/ST system without tandem FRET, the sensitivity of the CDs/ST@ZIF-8 toward TC increased ∼69-fold, and naked eye recognition could also be achieved. Furthermore, by analyzing the R, G, and B values of photos containing different concentrations of tetracycline with the help of a mobile phone and correlating them with the concentration of tetracycline, we can perform the on-site detection of tetracycline, which is convenient, fast, and accurate. This study shows that new insight can be gained for the rational design and application of ratiometric fluorescence sensors based on tandem Förster resonance energy transfer in metal-organic framework materials.