Functional nucleic acid-based fluorescent probes for metal ion detection

Metal ions are ubiquitous elements within our environments. Their excessive accumulation poses a great threat to human health. With the development of biology and bioanalytical chemistry, the role played by metal ions in many biological and chemical processes is revealed. Since trace amounts of metal ions can lead to essential influences, there is a growing demand for the study of highly sensitive and selective sensors. Among them, functional nucleic acid (FNA)-based fluorescent probes are proposed as ideal options. The programmability of FNA is constantly integrated with various kinds of fluorophores and strategies for efficient sensing assays. However, a comprehensive review of their advancements in medical and chemical areas is still needed. This review aims to summarize the FNA-based fluorescent methods for the detection and imaging of various metal ions. We focus on the unique properties of metal ions and versatile design strategies. In principle, each signaling strategy can be employed for different FNA-based sensors. Besides, the applications of DNA-templated nanomaterials, conformation-specific fluorophores and isothermal amplification are discussed. This comprehensive review can inspire more advanced fluorescent methods for metal ion sensing and promote the development of FNA for biomedical applications.