Developing a colorimetric method for the examination of lead ion (Pb2+) contamination in urine based on DNAzyme-functionalized magnetic particles with gold nanoparticles

Contamination of lead at high level in soil, ground water, vegetables and aquatic animals has become a serious worldwide environmental issue, is known as “Lead poisoning”.  Lead can be accumulated in bones and kidneys, and lead to seriously damage of nervous system and renal function, even exposed at low concentrations.  Conventional analytical methods from blood collection for lead detection rely on atomic absorption spectrometry, anodic stripping voltammetry (ASV) etc., which still require expensive operation, sophisticated instruments, as well as skilled personnel.  To overcome these limitations and allow on-site monitoring of lead, a facile and simple colorimetric assay was developed to detect Pb²⁺ using GR5-DNAzyme. Magnetic particles (MBs) and gold nanoparticles (AuNPs) were used as a signal collector and a signal indicator, respectively. We construct a DNAzyme-functionalised magnetic bead (MB).  In the presence of Pb²⁺, the substrate strand is cut into two pieces, resulting in the 70bp-GR5 DNAzyme still conjugated on MB.  After adding solution of AuNPs, the 70bp-GR5 DNAzyme will adsorb on AuNP through electrostatic interaction between base of single strand DNA with negative ion of citrate-stabilized on AuNP.  These remaining AuNPs will decrease, upon concentration of Pb²⁺.  In the absence of Pb²⁺, the substrate is still not cut and the GR5 DNAzyme will not adsorb on AuNP, causing negatively charge of phosphate backbone on double strand DNA.  The color of AuNPs is no change.  This developing sensor could possibly be used to potentially apply and serve as a general platform for on-site, naked eyes, and low-cost monitoring of other heavy metal ions in environmental and body fluid samples.