Hairpin oligosensor using SiQDs: Forster resonance energy transfer study and application for miRNA-21 detection

MicroRNAs are known to be tumor suppressors and promoters and can be used as cancer markers. In this work, a novel oligosensor was designed using Si quantum dots (SiQDs) for the detection of miRNAs. Five-nanometer SiQDs were synthesized, with a band gap of 2.8 eV, fluorescence lifetime of 4.56 mu s (tau(1/2) = 3.26 mu s), quantum yield of 25%, fluorescence rate constant of 6.25 x 10(4), and non-radiative rate constant of 1.60 x 10(5) s(-1). They showed excellent water dispersibility, good stability (with 95% confidence for 6-month storage) without photobleaching, and high biocompatibility, with an IC50 value of 292.2 mu g/L. The SiQDs and Black Hole Quencher-1 (BHQ1) were conjugated to the 5' and 3' terminals of an oligomer, respectively. The resulting hairpin molecular beacon showed resonance energy transfer efficiency of 63%. A distance of 0.91 R (Forster distance) between SiQD and BHQ1 was obtained. In the presence of a stoichiometric amount of the complementary oligonucleotide (Delta G(hybridization) = -35.09 kcal mol(-1)), 98% of the fluorescence was recovered due to loop opening of the hairpin structure. The probe showed good selectivity toward miRNA-21, with a limit of detection of 14.9 fM. The oligosensor recoveries of miRNA-21 spiked in human serum and urine were 94-98% and 93-108%, respectively.

Automated summary

A novel oligosensor using Si quantum dots (SiQDs) was designed and developed for the detection of miRNAs. This sensor showed high selectivity and sensitivity, and demonstrated good recovery rates in human fluid samples.