Development of a fluorescence-based DNAzyme biosensor to detect Pb2+ in tobacco leaf extracts for cleaner crop production

Abstract

Lead ions (Pb2+) are widespread contaminants that threaten human health and enter the human body mainly through the consumption of crop plants grown on Pb2+-contaminated soil. The traditional methods used to monitor the Pb2+ content of plants are sensitive and accurate; however, there is still an urgent need to develop screening methods with high sensitivity and reliability to rapidly monitor Pb2+ from plant samples with a higher throughput by adapting simple extraction methods. Here, we developed a series of fluorescence-based Pb2+ biosensors by fusing DNAzymes with tetrahedral DNA nanostructures and demonstrated the ability of these biosensors to detect Pb2+ in plant extracts. We first fused one DNAzyme with the A-probe of the tetrahedral DNA nanostructure. The substrate strand of the DNAzyme, which contains a ribonucleotide at its center, is cleaved upon Pb2+ binding, resulting in the release of the FAM fluorophore and the production of a fluorescence signal. The biosensors showed great sensitivity and selectivity. The sensitivity of the biosensor was further improved by fusing four DNAzymes to the tetrahedral DNA nanostructure and using Alexa488 as the fluorophore, which has greater quantum yield than FAM. Remarkably, the improved biosensors were able to detect Pb2+ in plant extracts. Thus, the Pb2+ biosensors developed in this study exhibit great potential for the identification and tracking of polluted regions by rapidly monitoring Pb2+ levels in plants grown therein and facilitating cleaner crop production.