Mechanically Stabilized UiO-66-NH2-MB Screen Printed Carbon Electrode for High Performance Electrochemical Ratiometric Quantification of miR-21-5p†

The ratiometric sensing strategy with dual-signal output drastically compensates for the background noise and interference from the detection environment of the sensing method with a single-signal output. However, the stability of the reference signal has become the primary challenge in constructing a ratio detection sensor. Therefore, in order to realize stable ratio signal sensing detection, methylene blue (MB) was encapsulated in the UiO-66-NH2 framework and printed as a reference signal inside a screen printed carbon electrodes (SPCE), which was helpful for the precise detection of miR-21-5p. Subsequently, based on the ultra-sensitive detection mechanism of catalytic hairpin assembly (CHA), the combination of miR-21-5p with H1 sequence on the Au-deposited SPCE triggered the loop-open of H1. After that, ferrocene labeled H2 (H2-Fc) and H3-Fc sequences were sequentially added to form a stable “T-shaped” structure, and miR-21-5p was released into the next cycle. Thus, the detection of miR-21-5p was quantified by the current ratio of Fc with MB, obtaining a ultra-low detection limit of 2.7 fM. This ratiometric sensing strategy based on SPCE offered a promising pathway for the highly sensitive sensing platforms.