Nano-Amplicon Comparator for Live Cell MicroRNA Imaging.

Live cell imaging as an investigative tool requires superior probe design to guarantee imaging quality and data validity. The ability to simultaneously address the robustness, sensitivity, and consistency issues in a single assay system is highly desired but remains a largely unsolved challenge. We describe herein a probe design strategy, nano-amplicon comparator (NAC), and demonstrate its proof-of-concept utility in intracellular microRNA (miRNA) imaging. This novel designer architecture builds upon spherical nucleic acid (SNA) for robustness, catalytic hairpin assembly (CHA) for sensitivity, and upconversion nanoparticle (UNP) for consistency. A catalytic circuit comprising a UNP-hairpin DNA (UNP-HDNA) conjugate and a hairpin DNA-organic fluorophore (HDNA-F) conjugate as probe responds to target miRNA and generates UNP-HDNA/HDNA-F complex as NAC for quantitative UNP-to-organic-fluorophore luminescent resonance energy transfer (LRET) imaging against a native UNP emission reference channel. Imaging application on miR21 shows the ability to monitor miRNA expression levels across different cell lines and under an external stimulus.