Alkaline earth metal ions, Ca 2+ and Mg 2+, play an important role in cell signaling including neurotransmission as well as their structural role and involvement in enzyme function. As the major metal ions in our body fluid, alkali metals ions, Na + and K + are responsible for maintenance of fluid and electrolyte balance, acid-base homeostasis, and maintenance of cell membrane potential allowing the generation of action potentials that are critical for neurotransmission, muscle contraction, and heart function. They are required in essential biological processes such as osmotic regulation, catalysis, metabolism, and cell signaling. Metal ions play crucial structural or functional roles in all life. This review summarizes the recent progress on the detection and imaging of the metal ions in biological systems including Na +, K +, Ca 2+, Mg 2+, Fe 2+/Fe 3+, Zn 2+, and Cu 2+ provides an opinion on remaining challenges to be addressed in this field. Among the various methods for metal ion detection, fluorescent sensors with organic dyes have attracted tremendous attention due to many advantages such as high fluorescence quantum yield, facile modification approaches and biocompatibility in addition to operation ease, high sensitivity, fast detection speed, and real-time detection. To understand various metabolic processes and facilitate diseases diagnosis, it is very important to measure the content and monitor the distribution of metal ions in individual cells, tissues and whole organisms. They can cause health problems when deficiency or excess occurs. Metal ions are widely present in biological systems and participate in many critical biochemical processes such as material transportation, energy conversion, information transmission and metabolic regulation, making them indispensable substance in our body.