DNAzyme-based colorimetric sensing of lead (Pb2+) using unmodified gold nanoparticle probes

Novel functional oligonucleotides, especially DNAzymes with RNA-cleavage activity, have been intensively studied due to their potential applications in therapeutics and sensors. Taking advantage of the high specificity of 17E DNAzyme for Pb²⁺, highly sensitive and selective fluorescent, electrochemical and colorimetric sensors have been developed for Pb²⁺. In this work, we report a simple, sensitive and label-free 17E DNAzyme-based sensor for Pb²⁺ detection using unmodified gold nanoparticles (GNPs) based on the fact that unfolded single-stranded DNA could be adsorbed on the citrate protected GNPs while double-stranded DNA could not. By our method the substrate cleavage by the 17E DNAzyme in the presence of Pb²⁺ could be monitored by color change of GNPs, thereby Pb²⁺ detection was realized. The detection of Pb²⁺ could be realized within 20 min, with a detection limit of 500 nM. The selectivity of our sensor has been investigated by challenging the sensing system with other divalent metal ions. Since common steps such as modification and separation could be successfully avoided, the sensor developed here could provide a simple, cost-effective yet rapid and sensitive measurement tool for Pb²⁺ detection and may prove useful in the development of sensors for clinical toxicology and environmental monitoring in the future.