科研之友
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摘要
In this study, a new isothermal signal amplification method is developed for sensitive detection of microRNAs (rniRNAs) by integrating the distinct advantages of graphene oxide (GO) for efficient fluorescence quenching of fluorophore-labeled single strand DNA (ssDNA) and double strand (ds)-specific nuclease (DSN) for highly selective digestion of DNA strand in DNA/RNA hybrids. DSN is a nuclease purified from hepatopancreas of Red King crab, which shows a strong preference for cleaving dsDNA and DNA in DNA/RNA hybrid duplexes. On contrast, DSN is practically inactive towards ssDNA or single- or double-stranded RNA. Herein, let-7a is selected as the proof-of-concept target miRNA and a fluorescein-labeled ssDNA probe is designed to be complementary to let-7a. The ssDNA probe, which will not be hydrolyzed by DSN in the absence of let-7a, will be adsorbed on GO via pi-pi stacking, resulting in efficient fluorescence quenching. When let-7a is introduced, it will hybridize with the ssDNA probe to form a double helix structure (dsDNA). DSN can selectively cleave the DNA oligonucleotides of the DNA/RNA hybrid to produce very small DNA fragments. Let-7a is thus released and will hybridize with another ssDNA probe again, which will be further cleaved by DSN. In this manner, each let-7a molecule can specifically trigger various cycles of hybridization and DSN cleavage of fluorescent ssDNA to yield numerous small fragments of DNA oligonucleotides. It should be noted that the pi-pi stacking interaction between GO and the very small DNA fragments bearing the fluorophores will be remarkably weakened, making the fluorescence maintained. Therefore, the DSN-mediated cycling of fluorescent ssDNA cleavage greatly amplifies the fluorescence signal for miRNA detection. Under the optimized experimental conditions, the fluorescence signal is proportional linearly to the concentration of let-7a in the range from 100 pmol/L to 5 nmol/L, and the detection limit is calculated to be 60 pmol/L (3 sigma). Furthermore, this proposed approach can also be applied to the simultaneous detection of multiplex miRNA targets.
