Metal–organic gel coupled entropy-driven circuit for fluorescence detection of miR-155

Abstract

Owing to their simple and convenient synthesis, the application of metal–organic gels (MOGs) in fluorescence detection has been increasingly studied. However, most relevant studies are based on the fluorescence changes of MOGs themselves caused by the direct interaction between the target and MOG, resulting in limited universality and insufficient sensitivity and other shortcomings. Thus, we combined a Cu-based metal–organic gel (Cu-MOG) with an entropy-driven circuit (EDC), as an isothermal enzyme-free amplification technique, to detect miR-155 as a proof-of-principle target. The substrate for the EDC was designed as a three-strand duplex (TD) containing an output strand (OS) which was modified with 6-carboxyfluorescein (FAM). In the presence of the target, namely miR-155, the EDC was triggered and OS was released, making the OS transition from the hybrid state to the free state. The fluorescence of the FAM modified free OS strand was then quenched owing to the intramolecular photo-induced electron transfer (PET) of the new ground state complex formed between the OS and MOG with a quenching constant of 1.48 mL μg⁻¹, which is much higher than that (0.08 mL μg⁻¹) of the hybrid state OS. This method provided a dynamic detection range of 1 nM to 5 nM with a detection limit of 0.23 nM for miR-155, demonstrating that the Cu-MOG coupled EDC has promising applications in bioassays, and opens up a new application field of MOGs in EDC development.