Development of DNAzyme Functionalized Magnetic Particles-Based Colorimetric Biosensor for Onsite Lead Ion Detection

Environmental contamination by the overuse of lead (Pb) in a variety of industries is the major cause of lead poisoning disease in Thailand. Medical diagnosis of this disease is quite complex and takes time as the pathology of this disease can occur in many organs and shows similar symptoms to other diseases. The analysis of Pb²⁺ content in human medical specimens is also limited in a laboratory as highly equipped analytical devices are required. To overcome these problems, we developed a rapid colorimetric biosensor for onsite Pb²⁺ detection in an aqueous solution using GR5 DNAzyme functionalized magnetic particles (MPs) and gold nanoparticles (AuNPs). With this platform, we found that Pb²⁺ catalyzing ribonucleotide phosphodiester bond cleavage of GR5 DNAzyme was completed within 1 minute with the aid of MPs to reduce the interference in the reaction. The fading of the colored AuNPs solution was detected after applying the external magnet to pull down the newly formed cleaved GR5 DNAzyme functionalized MPs-AuNPs complex, thus, decreasing the concentration of free AuNPs in the supernantant. The lowest concentration of Pb²⁺ that gave the observable signal by naked eye was 1 ppm while the calculated limit of detection was 0.905 ppm. This reaction was also highly specific to Pb²⁺ as no color changes were detected from the reaction between GR5 DNAzyme and other heavy metal ions. These findings suggested that our developed biosensor has the potential to be an alternative method for rapid and onsite Pb²⁺ detection in the future.