Abstract
A novel turn-off colorimetric sensor for sequence-specific recognition of single-stranded DNA (ssDNA) was established by combining Y-shaped DNA duplex and G-quadruplex-hemin DNAzyme. A G-rich single-stranded DNA (Oligo-1) displays peroxidase mimicking catalytic activity due to the specific binding with hemin in the presence of K+, which was able to catalyze the oxidation of colorless 2,2′-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS2−) by H2O2 to generate green ABTS•− radical for colorimetric assay. Oligonucleotide 2 (Oligo-2) was partly complementary with Oligo-1 and the target DNA. Upon addition of target DNA, Oligo-1, Oligo-2 and target DNA can hybridize with each other to form Y-shaped DNA duplex. The DNAzyme sequence of Oligo-1 was partly caged into Y-shaped DNA duplex, resulting in the inactivation of the DNAzyme and a sharp decrease of the absorbance of the oxidation product of ABTS2−. Under the optimum condition, the absorbance decreased linearly with the concentration of target DNA over the range of 1.0–250 nM and the detection limit was 0.95 nM (3σ/slope) Moreover, satisfied result was obtained for the discrimination of single-base or two-base mismatched DNA.
Highlights
Single nucleotide polymorphisms (SNPs) are single nucleotide variations that may be one-base substituted, deleted or inserted in a natural DNA sequence
Oligonucleotide 2 (Oligo-2) is used as assistant probe, which is partially complementary with Oligo-1 and target DNA
In the absence of target DNA, Oligo-1 does not hybridize with Oligo-2, and the free Oligo-1 can catalyze the oxidation of colorless 2,2′-azinobis(3-ethylbenzothiazoline)−6-sulfonic acid (ABTS2−) by H2O2 into green ABTS− radical
Summary
Single nucleotide polymorphisms (SNPs) are single nucleotide variations that may be one-base substituted, deleted or inserted in a natural DNA sequence. Two probes do not hybridize with each other without target DNA, but the hybridization occurs in the presence of target DNA through the formation of Y-shaped DNA duplex This structure is more sensible to single-base mismatch even under mild conditions since a relatively short duplex is formed between probes and target DNA13,14. DNAzyme has attracted more and more attention owing to its merits of high thermal stability, low cost, ease of preparation and purification as compared with natural protein enzymes[16,17]. Considering the advantages of colorimetric sensors and the catalytic effect of G-quadruplex-based DNAzyme, a series of sensors were constructed for the detection of metal ions[24], nucleic acid[25,26], protein[27,28] and small molecular[29,30]
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