A ratiometric FRET sensor using Ti₃C₂T_x MXene for intracellular microRNA-21 quantitative measurement

A ratiometric fluorescence resonance energy transfer (R-FRET) sensor based on two-dimensional Ti₃C₂T_x MXene nanosheets has been developed for intracellular miRNA-21 detection. The sensor comprises MXene nanosheets and two hairpin probes labeled with FAM (H1) and TAMRA (H2). MXene functions as a fluorescence quencher to suppress background noise, while FAM and TAMRA serve as the donor-acceptor FRET pair. Upon introduction of target miRNA-21, a catalyzed hairpin assembly (CHA) reaction is initiated, leading to the formation of an H1-H2 hybrid duplex. This brings the FAM and TAMRA fluorophores into proximity, facilitating efficient FRET. Quantitative detection of miRNA-21 is achieved by recording fluorescence spectra and calculating the intensity ratio (F_TAMRA/F_FAM). In vitro experiments demonstrated a linear response range from 100 pM to 20 nM with a limit of detection (LOD) of 40 pM. Furthermore, the sensor successfully quantified miRNA-21 expression levels within HeLa cells, indicating its potential as a promising platform for early cancer diagnosis.