Chemistry Reference
In-Depth Information
making the immobilized enzyme more fl exible. Therefore, enhanced electron trans-
fer was observed. Similar to other lead DNAzyme-based sensors, this electrochemi-
cal sensor was highly selective for Pb
2+
. A detection limit of 300 nM was reported
and the selectivity was comparable to those of the fl uorescent and colorimetric
sensors based on the same DNAzyme.
By immobilizing DNAzymes on a solid surface, an alternative sensing platform
can be built. Notably, this scheme will allow sensor regeneration, as well as long-term
storage of the sensor. In one report, the lead-specifi c 8 - 17 DNAzyme was covalently
attached to gold surfaces.
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In the presence of Pb
2+
, a fl uorophore - labelled substrate
fragment was cleaved and released into solution for detection. Thanks to a very low
background, a detection limit of 1nM was achieved. In another report, surface-
immobilized DNAzyme retained its activity even after storing in a dried state for
30 days at room temperature.
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A detailed characterization of this system was later
carried out.
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These studies will facilitate the application of DNAzymes in sensor
arrays for analysing complex targets.
14.6 Summary
Studies of DNAzymes represent an actively developing interdisciplinary fi eld involv-
ing many aspects of chemistry research, including biological, inorganic, physical and
analytical chemistry. In some ways, this fi eld has similarities to the study of ribozymes.
However, it also holds many new possibilities in exploring structural mechanisms
of functional nucleic acids and their biosensing applications. Despite recent
progresses, there is still a clear lack of understanding of how DNAzymes carry out
their catalytic functions, in comparison with our understanding of protein and RNA
enzymes. The three-dimensional structure of the DNAzyme in its active form con-
taining its cofactors has yet to be obtained. The structure features of the DNAzyme
will greatly help elucidate the underlying mechanism of DNAzyme-cofactor inter-
actions. In addition, analysis of the function of DNAzyme and its interactions with
the surrounding microenvironment at the molecular level using EPR, NMR,
smFRET, etc., is also in great need because they can provide valuable information
toward the ultimate understanding of DNAzyme activities. On the other hand, given
the current level of knowledge of DNAzymes, we have already been able to develop
DNAzymes with the desired properties in the presence of specifi c cofactors using
versatile
in vitro
selection. It will be of great signifi cance to actively extend the
family of DNAzymes in pursuit of a wider range of catalytic reactions that they can
carry out and an increasing number of cofactors that they can recruit. Due to the
fact that DNAs are inherently more stable than RNAs, these newly developed
DNAzymes are more suitable to be engineered into practical biosensors for many
different targets of interest. Additionally, with a large quantity of DNAzyme-based
sensors available, comprehensive sensor arrays can be built for highly reliable analy-
sis of complex samples. Given the increasing demand for convenient, economical
yet effective sensors, we will continue to witness rapid development and advanc-
ment of the DNAzyme sensing fi eld.
