Zn<sup>2+</sup>-Ligation
DNAzyme-Driven Enzymatic
and Nonenzymatic Cascades for the Amplified Detection of DNA
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Abstract
A generic fluorescence sensing platform for analyzing
DNA by the
Zn<sup>2+</sup>-dependent ligation DNAzyme as amplifying biocatalyst
is presented. The platform is based on the target DNA induced ligation
of two substrate subunits and the subsequent opening of a beacon hairpin
probe by the ligated product. The strand displacement of the ligated
product by the beacon hairpin is, however, of limited efficiency.
Two strategies are implemented to overcome this limitation. By one
method, a “helper” nucleic acid sequence is introduced
into the system, and this hybridizes with the DNAzyme components and
releases the ligated product for opening of the hairpin. By the second
method, a nicking enzyme (Nt.BspQI) is added to the system, and this
nicks the duplex between the beacon and ligated product while recycling
the free ligation product. By combining the two coadded components
(“helper” sequence and nicking enzyme), the sensitive
detection of the analyte is demonstrated (detection limit, 20 pM).
The enzyme-free amplified fluorescence detection of the target DNA
is further presented by the Zn<sup>2+</sup>-dependent ligation DNAzyme-driven
activation of the Mg<sup>2+</sup>-dependent DNAzyme. According to
this method, the Mg<sup>2+</sup>-dependent DNAzyme subunits displace
the ligated product, and the resulting assembled DNAzyme cleaves a
fluorophore/quencher-modified substrate to yield fluorescence. The
method enabled the detection of the target DNA with a detection limit
corresponding to 10 pM. The different sensing platforms are implemented
to detect the Tay–Sachs genetic disorder mutant