RNase DNAzyme for signal amplification. (a) Ligase/DNAzyme/MB sensor for ATP detection. ATP activates T4 DNA ligase to assemble a whole DNAzyme from two shorter DNA molecules; the DNAzyme cleaves a ribonucleotide (blue “R”) containing molecular beacon (MB) to generate a fluorescence signal. (b) DNAzyme/MB/endonuclease sensors for histidine. Histidine (His) activates the DNAzyme; the cleavage of the substrate by the DNAzyme produces a small DNA fragment (shown as the pink line) that bind an MB to assemble the recognition site (blue “X”) for a nicking endonuclease, which cleaves the MB to generate a fluorescence signal.
