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A highly sensitive and colorimetric biosensor based on magnetic nano-DNAzyme for detection of lead (II) ion in real water samples

BACKGROUND: Colorimetric 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. RESULTS: Magnetic 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 10² to 10⁸ pmol L‐¹, a limit of detection of 32 pmol L‐¹ and high selectivity for Pb²⁺ over other metal ions with an assay time less than 1 h. 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. CONCLUSION: The 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. © 2018 Society of Chemical Industry