DNAzymes metal-dependent

Fig. 4 Schematic representation of the metal-dependent 8-17 and 10-23 DNAzymes. The cleavage site in the RNA substrate strand (gray) is indicated by an arrow...

This chapter has presented an overview of applications of DNA in metal ion catalysis. Three general approaches were outlined metal-dependent DNAzymes, DNA-directed and templated catalysis, and DNA-based asymmetric catalysis. 

Since some DNAzymes depend on specific metal ions for activity, they can be employed for the detection of those ions, hi the first example, a previously reported [59] DNAzyme was labeled with a Dabcyl fluorescence quencher at the 3 -end and the corresponding RNA substrate with a TAMRA fluorophore at the 5 -end [60]. Upon addition of Pb " ions, the substrate was cleaved, resulting in dissociation from the DNA enzyme strand. This led to spatial separation of the fluorophore-quencher pair, resulting in fluorescence (Fig. 5). The sensor system was over 80 times more responsive to Pb than to other metal ions, and had a quantifiable detection range of 10 nM to 4 pM. A similar strategy was developed for the detection of Ctf by a DNAzyme that oxidatively cleaves DNA [61]. The system showed a dynamic range of 35 nM to 20 pM and had a metal ion selectivity of a factor of 2000 for Cu over other metal ions. A comparable system was reported for the detection of the uranyl cation (UO/ ), with millionfold selectivity over other metal ions and parts-per-trillion sensitivity. 

Dong s group reports a simple, sensitive, and label-free I7E DNAzyme-based sensor for Pb + detection. The catalytic activity of some DNAzymes is divalent metal ion-specific, just as the catalytic activity of some protein enzymes is metal ion cofactor-dependent (Santoro and Joyce, 1997 Carmi et al., 1998). In this work, the authors focus on 17E DNAzyme, which is a divalent Pb -specific enzyme employed widely in Pb + sensors (Santoro and Joyce, 1997). As shown in Figure 12.16A, in the presence of Pb, 17E DNAzyme could cleave the substrate 17DS, which could release ssDNA (including 17E and fragments from 17DS)... 

Metal Ion-Dependent DNAzymes and Their Applications as Biosensors... 

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