Trace and label-free microRNA detection using oligonucleotide encapsulated silver nanoclusters as probes.

A simple, sensitive, and label-free method for microRNA (miRNA) biosensing was described using oligonucleotide encapsulated silver nanoclusters (Ag-NCs) as effective electrochemical probes. The functional oligonucleotide probe integrates both recognition sequence for hybridization and template sequence for in situ synthesis of Ag-NCs, which appears to possess exceptional metal mimic enzyme properties for catalyzing H(2)O(2) reduction. The miRNA assay employs gold electrodes to immobilize the molecular beacon (MB) probe. After the MB probe subsequently hybridizes with the target and functional probe, the oligonucleotide encapsulated Ag-NCs are brought to the electrode surface and produce a detection signal, in response to H(2)O(2) reduction. An electrochemical miRNA biosensor down to 67 fM with a linear range of 5 orders of magnitude was obtained. Meanwhile, the MB probe allows the biosensor to detect the target with high selectivity. The Ag-NCs-based approach provides a novel avenue to detect miRNA with high sensitivity and selectivity while avoiding laborious label and signal amplification. It is convinced that rational introduction of signal amplification strategy to the Ag-NCs-based bioanalysis can further improve the sensitivity. To our best knowledge, this is the first application of the electrocatalytic activity of Ag-NCs in bioanalysis, which would be attractive for genetic analysis and clinic biomedical application.