Fluorescent probes for visualizing ion dynamics in bacteria: current tools and future perspectives

Ion gradients and membrane potential are fundamental to bacterial physiology, driving essential processes such as ATP synthesis, nutrient uptake, motility and stress adaptation. Visualizing these ion dynamics has become increasingly feasible through the use of fluorescent probes. This review provides a comprehensive overview of both synthetic dyes and genetically encoded indicators developed or adapted for bacterial systems. This review describes the principles underlying ion detection, highlights representative fluorescent probe tools and assesses their application in monitoring cytoplasmic ions and membrane potential in living bacterial cells. Specific challenges in bacterial imaging, such as cell size, membrane permeability, dye efflux and signal quantification, are discussed alongside recent advances in probe design and imaging platforms. This review aims to guide future research by outlining current capabilities, identifying limitations and suggesting opportunities for innovation in bacterial ion imaging.