Sensitive dual DNAzymes-based sensors designed by grafting self-blocked G-quadruplex DNAzymes to the substrates of metal ion-triggered DNA/RNA-cleaving DNAzymes
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Abstract
A universal label-free metal ion sensor design strategy was developed on the basis
of a metal ion-specific DNA/RNA-cleaving DNAzyme and a G-quadruplex DNAzyme. In this
strategy, the substrate strand of the DNA/RNA-cleaving DNAzyme was designed as an
intramolecular stem-loop structure, and a G-rich sequence was caged in the double-stranded
stem and could not form catalytically active G-quadruplex DNAzyme. The metal ion-triggered
cleavage of the substrate strand could result in the release of the G-rich sequence
and subsequent formation of a catalytic G-quadruplex DNAzyme. The self-blocking mechanism
of the G-quadruplex DNAzyme provided the sensing system with a low background signal.
The signal amplifications of both the DNA/RNA-cleaving DNAzyme and the G-quadruplex
DNAzyme provided the sensing system with a high level of sensitivity. This sensor
design strategy can be used for metal ions with reported specific DNA/RNA-cleaving
DNAzymes and extended for metal ions with unique properties. As examples, dual DNAzymes-based
Cu(2+), Pb(2+) and Hg(2+) sensors were designed. These "turn-on" colorimetric sensors
can simply detect Cu(2+), Pb(2+) and Hg(2+) with high levels of sensitivity and selectivity,
with detection limits of 4 nM, 14 nM and 4 nM, respectively.