A Portable Sensor Based on DNA Walker Signal Amplification for Detection of Pb²⁺

A sensitive and convenient sensor for detection of Pb2+ was established based on the specific recognition of Pb2+ and substrate DNA (sDNA), coupling with Fe3O4 nano-magnetic beads (MB) as sensor platform, portable glucose meter (PGM) as signal capture terminal and DNA walking device as signal amplification strategy. The nanogold-functionalized Poly (amidoamine) (Au/PAMAM) dendrimers prepared by reduction method were modified by glucose oxidase (GOx) and sDNA to form sDNA/GOx/ Au/PAMAM complex. Based on the complementary base pairing principle, the sDNA/GOx/Au/PAMAM complex was captured on the MB modified by capture DNA (cDNA), and the DNA enzymes (DNAzyme) could bind to the un-paired parts of sDNA. In the presence of target, Pb2+ could specifically recognize cleavage sites on sDNA and shear it, meanwhile released DNAzyme and GOx/Au/PAMAM. The former continued to bind with the next sDNA, and then the new identification-split-release circulation was opened. The circulation could be called DNA walker device, and the release quantity of GOx/Au/PAMAM was increased to realize signal amplification. The supernatant (GOx/Au/PAMAM), separated by magnetic separation, could oxidize glucose (Glu) in the reaction solution, and the change value of Glu concentration was monitored with PGM, thus indirectly detecting the target Pb2+ concentration. Under the optimal conditions, the PGM response of the system showed a good linear relationship with the logarithm of Pb2+ concentration ranging from 1.00 pmol/L to 1.00 mu mol/L, and the detection limit was 0.66 pmol/L.