SPQ is primarily used as a fluorescent probe in biological and chemical research to study chloride ion transport and concentration in various systems. It is particularly valuable in cellular studies, where it helps monitor chloride ion dynamics in living cells, providing insights into cellular function and ion channel activity. SPQ's fluorescence is quenched by chloride ions, making it a sensitive tool for measuring chloride levels in solutions, tissues, and cells. It is also employed in research related to cystic fibrosis, as it aids in understanding chloride ion movement across cell membranes, which is critical in this condition. Additionally, SPQ is used in environmental studies to assess chloride ion concentrations in water samples, contributing to water quality analysis.