In Situ Enzymatic Generation of Metal-Organic Frameworks for Target-Gated Electrochemiluminescence Detection of miRNA.

Metal-organic frameworks (MOFs) hold great promise in electrochemiluminescence (ECL) biosensing; however, their applications are severely restricted by a cumbersome preparation procedure and low emission efficiency. In order to address these challenges, we developed a novel MOF-based ECL biosensor via an in situ generation strategy. The Cd-MOF employed herein was prepared by the reaction of Cd with the ligand (TCBPA) in the presence of ammonia, enabling rapid synthesis within minutes under a mild environment, thus greatly simplifying the operation processes. Within the periodically ordered framework, the TCBPA molecules were spatially confined, with suppressed nonradiative transitions, thereby generating enhanced ECL signals. Inspired by the rapid formation of Cd-MOF in the presence of ammonia, the in situ generation of MOFs on the electrode was realized through urease-catalyzing decomposition of urea to ammonia, thereby leading to "off-on" ECL emission transiently. Since urease was introduced onto the electrode in the presence of target miRNAs, this target-gated ECL sensing strategy was established with a wide linear detection range from 1.0 fM to 1.0 nM for the thyroid cancer marker miRNA-146b-5p, and a detection limit as low as 0.59 fM, along with concise operation and rapid response. The target-gated generation of MOF emitters not only achieved unprecedented specificity and exceptional signal-to-noise ratio, but also expanded the applications of MOF-based ECL in biosensing.