Ratiometric FRET encoding Zr-MOF@Au-FAM/TAMRA nano assemblies based on tetrahedral framework nucleic acid-functionalized magnetic beads and DNA walker for ultrasensitive quantifying enrofloxacin and ciprofloxacin

Quinolone-antibiotic residues pose serious threat to food safety and ecological environmental health. Therefore, we have developed a ratiometric FRET encoding Zr-MOF@Au-FAM/TAMRA (ZAFT) nano assemblies based on tetrahedral framework nucleic acid-functionalized magnetic beads (W/Apt-Tet-MB) and DNA walker for ultrasensitive quantification of two typical quinolone antibiotics (enrofloxacin and ciprofloxacin). Firstly, a simple and stable satellite nano assembly (Zr-MOF@AuNPs) was synthesized. DNA hairpin H1-L@FAM was coupled with Zr-MOF@AuNPs to form Zr-MOF@Au@FAM (ZAF) nano assembly. Furthermore, the W/Apt-Tet-MB demonstrated excellent capturing capability for ENR and CIP due to the efficient integration of group-specific aptamer in the DNA tetrahedra. In addition to capturing targets, the walker DNA (W) was released, triggering the opening of DNA H1 on the ZAF. Supported by fuel DNA H2 and entropy-driven mechanisms, the newly exposed ssDNA region within H1 then reacted with H2 and reporter DNA (modified with Tamra) through nucleic acid hybridization to form ZAFT and release W again. Subsequently, the released W opened other nearby H1 and continuously initiated a new round of DNA walker reaction. Thus, ZAFT was generated in large quantities. Meanwhile, significant ratiometric fluorescence signals (F585/F519) were generated and positively correlated with the amounts of targets employing the localized surface plasmon resonance (LSPR) activities of prepared Zr-MOF@AuNPs. The developed aptasensor demonstrated good linearity in the 0.001–100 ng/mL range, with a LOD of 0.24 and 0.31 pg/mL towards ENR and CIP. Importantly, the aptasensor was successfully applied to quantify ENR/CIP in real samples with satisfactory recoveries, manifesting its prospective application in environmental monitoring and food safety.