There are many sophisticated instrumental methods available to detect metal ions in the environment; it is more desirable to perform on-site real-time detection of the metal in the environment. Therefore, the development of biosensors\' for the on-site detection of metal ions is an increasing interest among researchers. DNA has been known as the reservoir of genetic information, and DNA has been least used to develop biosensors. But the discovery of DNA enzyme (DNAzyme) revolutionized metal detection via biomolecules. DNA is highly stable, easily synthesized, cost-effective, and DNA can be easily modified to alter its functions compared to other biomolecules. These DNAzymes are capable of detecting metal ions via their catalytic activity with high selectivity. Incorporating the fluorophore into the DNAzyme to make them fluorescence creates a new platform to develop novel biosensors. Recently, the utilization of the DNAzymes to detect metal ions in the environment has shifted towards the intracellular sensing and imaging of the metal ions, theranostic applications, and microorganisms\' detection due to its unique properties. In this review, we are focus on the critical analysis of the functional nucleic acids, in-vitro selection, isolated metal-specific DNAzymes that correspond to the development of biosensors from the early \'90s to the present. Furthermore, the significance of fluorescence incorporation to DNA, a detailed summary of fluorescence-based DNAzyme sensors, and how different types of fluorescence techniques such as fluorescence anisotropy, two-photon (TP) fluorescence are utilized in the development of biosensors, and applications of the DNAzyme in various fields are critically analyzed.