A ratiometric fluorescent biosensor based on self-fluorescent MOF and target-triggered rolling circle amplification for sensitive detection of exosome-derived miRNA

MicroRNAs (miRNAs) are considered as biomarkers and display great potential in the diagnosis of diseases. As a colorectal cancer (CRC)-associated miRNA biomarker, miR-92a-3p possesses higher concentration in exosomes than in serum, causing it more feasible to diagnose CRC by measuring the concentration of miR-92a-3p inside exosomes. Herein, a rationally-engineered ratiometric fluorescent biosensor is proposed to detect the concentration of exosomal miR-92a-3p. The metal-organic framework (MOF-525) with self-fluorescence serves as both a fluorescent reference and a quencher of the fluorescence of single-stranded reporter by adsorption. The presence of miR-92a-3p triggers the looping of 5P-template strand and the further periodic rolling circle amplification. The periodic long strands and the reporters can form double strands to prevent the reporters from being adsorbed by MOF-525. The concentration of miR-92a-3p is positively correlated with the Δreporter/MOF-525 fluorescence intensity ratio. The biosensor exhibits a detection range of 0.1-10 pM and can differentiate miR-92a-3p from mismatched RNA sequences. The accuracy and practicality of the proposed biosensor for exosomal miRNA detection were evaluated by comparing with the conventional RT-qPCR. The as-obtained results are close to those of the RT-qPCR. This ratiometric fluorescent biosensor holds the potential for the sensitive detection of exosomal miRNA.