Intracellular self-enhanced rolling circle amplification to image specific miRNAs within tumor cells

MicroRNAs (miRs) are a class of non-coding, small RNA molecules that play important roles in gene expression. The aberrant expression of miRs is associated with various human diseases, and miRs have been regarded as biomarkers and therapeutic targets in cancer treatment. In this work, using miR-21 as model target species, an efficiently self-enhanced rolling circle amplification (seRCA)-based biosensing platform was developed for the ultrasensitive detection of cancer-related miRs. In the presence of target, a linear DNA template can be cyclized by ligase and initiate the first RCA (fRCA) reaction. Without any separation step and chemical modification, the fRCA products (fRCAp) are capable of activating the second exponential RCA and produce a much higher fluorescence signal, causing the self-enhancement effect of RCA reaction. Because two different signal amplification processes are introduced, there are two linear dynamic ranges together over 7 orders of magnitude. Target miR can be detected down to 1.0 fM with very high specificity, eliminating the interference from homologous miRs. If a fluorescently modified oligonucleotide probe is involved, the seRCA-based biosensing strategy is able to be employed for the intracellular imaging of cancer-related miR. Significantly, the comparative evaluation demonstrates that the proposed strategy exhibits the impressive capability to execute the miR imaging within cells higher than classical fluorescence in situ hybridization (FISH) method. The newly-developed powerful sensing strategy for the specific miR imaging would offer a unique opportunity to promote molecular biological research, early diagnosis and treatment of human cancers.