Colorimetric and energy transfer based fluorometric turn-on method for determination of microRNA using silver nanoclusters and gold nanoparticles.

The authors describe a dual (colorimetric and fluorometric) detection scheme for microRNA. The method is based on the use of fluorescent DNA-modified silver nanoclusters (DNA-AgNCs) and gold nanoparticles (AuNPs). The DNA-AgNCs were linked to AuNPs via the interaction of ssDNA-AgNC probes with AuNPs. This led to quenching of the fluorescence of the DNA-AgNCs (best measured at excitation/emission peaks of 370/450 nm) and also prevents salt-induced aggregation of the AuNPs. Upon addition of microRNA, the DNA on the AgNCs hybridizes with microRNA. This led to the formation of a DNA-AgNC/miRNA hetero-duplex and increase of the distance to the AuNPs. Quenching was suppressed and fluorescence was restored. The presence of microRNA also affected salt-induced particle aggregation as reflected by a color change from red to purple that is visible with bare eyes. The visual detection limit for microRNA is 0.6 nM, and the fluorometric detection limit is 0.4 pM. Graphical abstract Schematic of the colorimetric and fluorometric assay for microRNA (miRNA). It is based on the use of fluorescent DNA-modified silver nanoclusters (AgNCs) and gold nanoparticles (AuNPs).