Functional nucleic acid sensors, including aptamers and nucleic acid enzymes (NAEs), offer advantages over traditional antibody-based sensors. Aptamers, selected through in vitro methods, can bind a wide range of targets with high affinity and specificity, making them suitable for detecting ions, molecules, and toxins. NAEs, such as DNAzymes and ribozymes, can catalyze various reactions and are used for metal detection. DNAzymes are particularly useful for sensing due to their stability, cost-effectiveness, and ease of synthesis. Aptamers are selected through in vitro selection (SELEX) and can be tailored to bind specific targets. They are highly specific and can be modified for enhanced stability. NAEs, including DNAzymes, are used for metal sensing, with DNAzymes showing high catalytic efficiency and specificity. For example, the 8-17 DNAzyme is specific for Pb²⁺ and can detect it at concentrations as low as 10 nM. Fluorescent NAE sensors use catalytic beacons, where fluorescence changes upon metal binding. These sensors can detect metals like Pb²⁺ and UO₂²⁺ with high sensitivity. For instance, a Pb²⁺ sensor using a catalytic beacon showed a 300% fluorescence increase in the presence of Pb²⁺. Similarly, a UO₂²⁺ sensor achieved a detection limit of 45 pM. Colorimetric NAE sensors rely on changes in the optical properties of gold nanoparticles (AuNPs) upon metal binding. For example, a Pb²⁺ sensor using AuNPs showed a red-to-blue color change in the presence of Pb²⁺. The dynamic range of such sensors can be tuned by modifying DNAzyme sequences, allowing detection over a wide concentration range. Immobilized DNAzymes on surfaces or in microfluidic devices enhance sensor performance and stability. For instance, a Pb²⁺-specific DNAzyme immobilized on gold surfaces achieved a detection limit of 1 nM. Additionally, peroxidase-like DNAzymes can amplify signals through catalytic reactions, enabling detection of low concentrations of metals and other analytes. These sensors have applications in environmental monitoring, medical diagnostics, and industrial quality control. Their ability to detect metals with high sensitivity and specificity makes them valuable tools for various sensing applications.Functional nucleic acid sensors, including aptamers and nucleic acid enzymes (NAEs), offer advantages over traditional antibody-based sensors. Aptamers, selected through in vitro methods, can bind a wide range of targets with high affinity and specificity, making them suitable for detecting ions, molecules, and toxins. NAEs, such as DNAzymes and ribozymes, can catalyze various reactions and are used for metal detection. DNAzymes are particularly useful for sensing due to their stability, cost-effectiveness, and ease of synthesis. Aptamers are selected through in vitro selection (SELEX) and can be tailored to bind specific targets. They are highly specific and can be modified for enhanced stability. NAEs, including DNAzymes, are used for metal sensing, with DNAzymes showing high catalytic efficiency and specificity. For example, the 8-17 DNAzyme is specific for Pb²⁺ and can detect it at concentrations as low as 10 nM. Fluorescent NAE sensors use catalytic beacons, where fluorescence changes upon metal binding. These sensors can detect metals like Pb²⁺ and UO₂²⁺ with high sensitivity. For instance, a Pb²⁺ sensor using a catalytic beacon showed a 300% fluorescence increase in the presence of Pb²⁺. Similarly, a UO₂²⁺ sensor achieved a detection limit of 45 pM. Colorimetric NAE sensors rely on changes in the optical properties of gold nanoparticles (AuNPs) upon metal binding. For example, a Pb²⁺ sensor using AuNPs showed a red-to-blue color change in the presence of Pb²⁺. The dynamic range of such sensors can be tuned by modifying DNAzyme sequences, allowing detection over a wide concentration range. Immobilized DNAzymes on surfaces or in microfluidic devices enhance sensor performance and stability. For instance, a Pb²⁺-specific DNAzyme immobilized on gold surfaces achieved a detection limit of 1 nM. Additionally, peroxidase-like DNAzymes can amplify signals through catalytic reactions, enabling detection of low concentrations of metals and other analytes. These sensors have applications in environmental monitoring, medical diagnostics, and industrial quality control. Their ability to detect metals with high sensitivity and specificity makes them valuable tools for various sensing applications.