Rational Design of 'Turn-On' Allosteric DNAzyme Catalytic Beacons for Aqueous Mercury Ions with Ultrahigh Sensitivity and Selectivity

摘要

Mercury is a highly toxic heavy metal in the environment. Mercury exposure can cause a number of severe adverse health effects, such as damage in the brain, nervous system, immune system, kidney, and many other organs. Mercury contamination comes from nature as well as from human activities, and an annual release of 4400 to 7500 metric tons of mercury into the environment was estimated by the United Nations Environment Programme (UNEP). Therefore, highly sensitive and selective mercury sensors are very useful in understanding its distribution and pollution and in preventing mercury poisoning. Towards this goal, many fluorescent small-organic-molecule-based Hg~(2+) ion sensors have been reported, which change their emission properties upon binding to Hg~(2+) ions. Most of these sensors, however, require the involvement of organic solvent, show quenched emissions, and suffer from poor selectivity. Only a few such sensors can detect Hg~(2+) ions in water with high sensitivity and selectivity. Hg~(2+)-ion sensors based on foldamers, oligonucleotides, conjugated polymers, genetically engineered cells, enzymes, antibodies, transcriptional regulatory proteins, DNAzymes, and chemically modified optical fibers, capillary optodes, membranes, electrodes, mesoporous silica, and nanoparticles are also known. For environmental-monitoring applications, such as detection of Hg~(2+) ions in drinking water, a detection limit of lower than 10 nM (the toxic level defined by the U.S. Environmental Protection Agency (EPA)) is required. However, few reported mercury sensors can reach such sensitivity. We are interested in using catalytic DNA or DNAzymes to design metal sensors that can achieve the goal.