Paper-based scanometric assay for lead ion detection using DNAzyme

•We construct a magnetic bead (MB)-DNAzyme-AuNPs complex to ease Pb2+ detection.•Pb2+ cleaves the DNAzyme and lead to disassembly of AuNPs from the MB.•Solution of AuNPs is collected on a paper and amplifies through silver reduction method.•This sensing platform can detect Pb2+ as low as 0.3 nM.•This method could be used to monitor Pb2+ in environmental and body fluid samples.

A facile and simple paper-based scanometric assay was developed to detect Pb2+ using GR5-DNAzyme. Magnetic beads (MBs) and gold nanoparticles (AuNPs) were used as a signal collector and a signal indicator, respectively. They were linked together by GR5-DNAzyme, comprising an enzyme and a substrate strand pairing up with each other. In the presence of Pb2+, the substrate strand is cut into two pieces, resulting in the disassembly of AuNPs from the MBs. These AuNPs were spotted on predefined areas on a chromatography paper, where signal is amplified through silver reduction. This sensing platform exhibits high sensitivity and selectivity toward Pb2+, giving a detection limit of 0.3 nM and a linear fitting range from 0.1 to 1000 nM. Testing of this biosensor in river water and synthetic urine samples also showed satisfying results. Besides offering simultaneous and multi-sample analysis, this paper-based sensing platform presented here could be potentially applied and served as a general platform for on-site, naked eyes, and low-cost monitoring of other heavy metal ions in environmental and body fluid samples.

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