Using silver nanoclusters to detect cancer-associated micro-RNA sequences.

DNA-templated silver nanoclusters (AgNC@DNA) are a novel type of nanomaterials with advantageous optical properties. Only a few atoms in size – the fluorescent of nanoclusters can be tuned using loose DNA overhangs. In this study, we explore the properties of AgNC manufactured on a short single-stranded 12 cytosines long DNA fragment. We observe differences between designs containing the same AgNC templating sequence – twelve consecutive cytosines, (dC)12, when adjacent G-rich sequences (dGN, with N=3-15) are added. The single "basic" element, C12, emits in "red" with lambda max = 635 nm (red). Addition of G-rich overhang with NG=15 dramatically changes the pattern of the Emission-Excitation Matrix (EEM) with two new emission peaks appearing λ1 = 575 nm (green) and λ2 = 700 nm (far-red). The appearance of these peaks provides a novel way for the design of biosensors capable of detecting specific nucleic acid sequences. We have used this property to construct an NA 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 have tested this detecting switch on miR-371a-3p, which is typically overexpressed in testicular cancer, thus providing evidence that such a novel fluorescent switch is both sensitive and specific.