The development of a simple sensor (9NL27-Zn) based on DNAzyme and PCR and aimed at the detection of low concentrations of zinc (II) ions is described. A specific Zn(II)-dependent DNAzyme (9NL27) with DNA-cleaving activity was employed. In the presence of zinc (II), the DNAzyme hydrolyzed DNA substrate into two pieces (5′ and 3′ fragments), forming 3′-terminal hydroxyl in the 5′ fragment and 5′-phosphate in the 3′ fragments. Subsequently, the 5′ fragment left the DNAzyme and bound a short DNA template. The 5′ fragment was used as a primer and extended a single-stranded full-length template by Taq polymerase. Finally, this full-length template was amplified by PCR. The amplified products had a quantitative relationship with Zn(II) concentration. Under our experimental conditions, the DNA sensor showed sensitivity (10 nM) and high specificity for zinc ion detection. After improvement of the DNA sensor, the detection limit can reach 1 nM. The simple DNA sensor may become a DNA model for the detection of trace amounts of other targets.

Design and switch of catalytic activity in enzymology remains a subject of intense investigation. Here, we employ a DNAzyme–RNAzyme combination strategy for construction of a 10–23 deoxyribozyme-hammerhead ribozyme combination that targets different sites of the β-lactamase mRNA. The 10–23 deoxyribozyme-hammerhead ribozyme combination gene was cloned into phagemid vector pBlue-scriptIIKS (+). In vitro the single-strand recombinant phagemid vector containing the combination sequence exhibited 10–23 deoxyribozyme activity, and the linear transcript displayed hammerhead ribozyme activity. In bacteria, the 10–23 deoxyribozyme-hammerhead ribozyme combination inhibited the β-lactamase expression and repressed the growth of drug-resistant bacteria. Thus, we created a DNAzyme–RNAzyme combination strategy that provides a useful approach to design and switch of catalytic activities for nucleic acid enzymes.