Detection of cancer-associated miRNA using fluorescence switch of AgNC@NA and guanine-rich overhang sequences.

DNA-templated silver nanoclusters (AgNC@DNA) are a novel type of nanomaterials with advantageous optical properties. Only a few atoms in size - the fluorescence of nanoclusters can be tuned using DNA overhangs. In this study, we explore the properties of AgNC manufactured on a short single-stranded (dC) 12 when adjacent G-rich sequences (dG N , with N=3-15) are added. The "red" emission of AgNC@dC 12 with λ MAX = 660 nm dramatically changes upon addition of a G-rich overhang with N G =15. The pattern of the Emission-Excitation Matrix (EEM) suggests the emergence of two new emissive states at λ MAX = 575 nm and λ MAX = 710 nm. The appearance of these peaks provides an effective way for the design of biosensors capable of detecting specific nucleic acid sequences with low fluorescence background. We have used this property to construct a NA-based switch that brings AgNC and G-overhang near one another turning "ON" the new fluorescence peaks only when a specific miRNA sequence is present. Next, we tested this detecting switch on the miR-371 which is overexpressed in prostate cancer. The results presented provide evidence that such a novel fluorescent switch is both sensitive and specific with the limit of detection close to 22 picomoles of the target miR-371 molecule.