A reusable fluorescent biosensor based on a morphology-controlled ZIF-8⊃FAM-DNA film

As a promising porous material, zeolitic imidazolate framework-8 (ZIF-8) exhibits significant application potential in biosensing. However, its reusability in the solution form is limited. In this work, a reusable ZIF-8⊃FAM-DNA film biosensor is fabricated by assembling FAM-labeled single-stranded (ss) DNA with a ZIF-8 film, whose crystal morphology is controlled via surfactants. The morphology, crystal structure, specific surface area and electrostatic adsorption capacity of ZIF-8 crystals are characterized, where the rhombohedral dodecahedral shaped ZIF-8 crystal is the optimal choice due to its moderate positive surface potential and low roughness. Thus, the highest fluorescence quenching efficiency of 79.4% is achieved in the presence of the ZIF-8 film with this crystal shape. Then, the target HIV-1 ssDNA induces specific hybridization with FAM-DNA to form rigid double-stranded DNA, which results in significant fluorescence recovery. Notably, the fluorescence recovery sensitivity of the film biosensor with rhombohedral dodecahedral shaped ZIF-8 crystals reaches 0.080 nM^-1 with a detection limit of 3.66 nM (based on the 3σ method). More importantly, the film biosensor can maintain a quenching efficiency of 75.0% and a recovery efficiency of 336.1% after three consecutive quenching-recovery cycles, demonstrating its good repeatability. Furthermore, after being stored in a vacuum for 5 days, the film biosensor retains a recovery efficiency of 415.0%, demonstrating a quite good stability. This work provides a practical and reusable MOF-based sensing platform for biological detection.