Simultaneous fluorescent detection of multiple metal ions based on the DNAzymes and graphene oxide

A novel fluorescent detection strategy for simultaneous detection of Cu²⁺, Pb²⁺ and Mg²⁺ based on DNAzyme branched junction structure with three kinds of DNAzymes and graphene oxide (GO) was presented. Three fluorophores labeled DNA sequences consisted with enzyme-strand (E-DNA) and substrate strand (S-DNA) were annealed to form DNAzyme branched junction structure. In the presence of target metal ion, the DNAzyme was activated to cleave the fluorophore labeled S-DNA. The S-DNA fragments were released and adsorbed onto GO surface to quench the fluorescent signal. The detection limit was calculated to be 1 nM for Cu²⁺, 200 nM for Mg²⁺, and 0.3 nM for Pb²⁺, respectively. This strategy was successfully used for simultaneous detection of Cu²⁺, Mg²⁺ and Pb²⁺ in human serum. Moreover, it had potential application for simultaneous detection of multiple metal ions in environmental and biological samples.