Hairpin DNA probe with 5′-TCC/CCC-3′ overhangs for the creation of silver nanoclusters and miRNA assay

• A short cytosine-rich oligonucleotide served as a scaffold for AgNCs creation.
• The AgNCs/hairpin ODN probe was used for miRNA assay.
• The method exhibits high sequence specificity.
• The sensing protocol is simple and cost-effective.

A facile strategy for the assay of target miRNA using fluorescent silver nanoclusters (AgNCs) has been described. Due to the preferable interaction between cytosine residues and Ag+, a short cytosine-rich oligonucleotide (ODN) with only six bases 5′-TCCCCC-3′ served as an efficient scaffold for the creation of the AgNCs. The AgNCs displayed a bright red emission when excited at 545 nm. Such ODN base-stabilized AgNCs have been exploited for miRNA sensing. Overhangs of TCC at the 5′ end (5′-TCC) and CCC at the 3′ end (CCC-3′) (denoted as 5′-TCC/CCC-3′) appended to the hairpin ODN probe which also contains recognition sequences for target miRNA were included. Interestingly, the AgNCs/hairpin ODN probe showed similar spectral properties as that templated by 5′-TCCCCC-3′. The formation of the hairpin ODN probe/miRNA duplex separated the 5′-TCC/CCC-3′ overhangs, thus disturbing the optical property or structure of the AgNCs. As a result, fluorescence quenching of the AgNCs/hairpin ODN probe was obtained, which allows for facile determination of target miRNA. The proposed method is simple and cost-effective, holding great promise for clinical applications.