Förster Resonance Energy Transfer-Based Soft Nanoballs for Specific and Amplified Detection of MicroRNAs

Förster resonance energy transfer (FRET) by using fluorescent carbon dots (CDs) as energy donors shows potential for biosensing and bioimaging. However, it remains underused and underestimated for CDs as a building block for FRET owing to the low efficiency and complex operation originating from the surface modification of CDs. To overcome these limitations, herein we develop a novel FRET soft nanoball (fretSNB) in which thousands of green CDs and black hole quencher 2 (BHQ-2) dyes are loaded, and FRET occurs from CDs to BHQ-2 dyes with the consequence of effective fluorescence quenching. These fretSNBs can be ruptured in the presence of phospholipase A₂ (PLA₂) released in a process of duplex-specific nuclease (DSN)-assisted target recycling amplification (TRA), making the fluorescence of CDs recovered. Thus, a dual amplification strategy is successfully developed for amplified detection of microribonucleic acids (miRNAs) in the concentration range 0.025-10 nM with a limit of detection (3σ) reaching 16.5 pM which is about 515 times lower than without fretSNBs. In addition, the developed strategy exhibits high selectivity for discrimination of a single nucleotide difference and capability to detect miRNAs extracted from cells, suggesting excellent potential in biomedical analysis and clinical diagnosis.