Carbon nanodot-based self-delivering microRNA sensor to visualize microRNA124a expression during neurogenesis

MicroRNAs (miRNAs, miRs) are recognized as regulators of gene expression related to cellular development and diseases. In this study, we developed a carbon nanodot (C-dot)-based miR124a molecular beacon (miR124a CMB). The C-dots were purified from candle soot (cC-dots) by thermal oxidation. The double-stranded DNA oligonucleotide containing a miR124a binding site and black hole quencher 1 (miR124a sensing oligo) was further conjugated with the cC-dots to form the miR124a CMB. P19 cells were incubated with the miR124a CMB to sense miR124a expression during neurogenesis. The physical properties of the cC-dots showed multi-color light emission with various excitation wavelengths, a broad size distribution ranging from 2 to 4 nm, a graphitic carbon core (sp²), an abundance of carboxyl groups on the surface, no evidence of cellular toxicity and a high level of self-promoted uptake into cells. The miR124a CMB showed great fluorescence quenching in the absence of miR124a. The miR124a CMB internalized into P19 cells successfully visualized a gradual increase in miR124a expression during neuronal differentiation by providing signal-on imaging activity acquired by the following mechanism: the miR124a, which was highly expressed during neurogenesis, was bound to the miR124a binding site, resulting in the detachment of the quencher from the miR124a CMB and producing fluorescence recovery. The miR124a CMB demonstrated great specificity for sensing miR124a biogenesis with the advantages of self-passivated carboxyl groups, no toxicity, and self-illumination and highly self-promoted cellular uptake which will make the sensing of other various miRNAs related to diseases easy, convenient and accurate.