BACKGROUNDColorimetric biosensors based on DNAzyme provide convenient and selective means for the detection of lead ion (Pb2+), which are critically important to prevent lead exposure and poisoning. However, they still remain challenging because of their limitation of sensitivity (only nmol L-1 level) and practical application. Herein, we design a highly sensitive, selective, simple, and quantitative platform for direct Pb2+ detection based on the magnetic nano-DNAzyme in real water samples. RESULTSMagnetic beads were modified with enzyme strand of DNAzyme to work as solid phase carriers and hybridized with DNAzyme's substrate strand/horseradish peroxidase molecules double-codified gold nanoparticles to form a stable magnetic nano-DNAzyme complex. Under the optimized reaction conditions, the magnetic nano-DNAzyme had a quantitative detection range from 10(2) to 10(8)pmol L-1, a limit of detection of 32pmol L-1 and high selectivity for Pb2+ over other metal ions with an assay time less than 1h. In addition, this method showed enhanced pH stability and long service life, and had a potential to detect other metal ions only by changing corresponding DNAzyme specific to them. Finally, the magnetic nano-DNAzyme platform was demonstrated to work well in direct Pb2+ detection in real water samples. CONCLUSIONThe magnetic nano-DNAzyme system for colorimetric detection of Pb2+ showed high sensitivity and selectivity, simple, enhanced pH stability with long service life in practical application. (c) 2018 Society of Chemical Industry