How does SBFI work as a sodium indicator?

Sodium imaging techniques rely on the signals generated by fluorescent Na+ indicators (e.g SBFI). SBFI dyes are made out of an ion binding site and out of parts which emit light when illuminated. When sodium ions bind to the dye, it causes the dye to undergo conformational changes, and is then followed by spectral alterations. The spectral changes are analyzed at specific wavelengths that cause fluorescence and then measuring the emitted light. The emitted light is then detected and displayed using software for analysis. SBFI dyes offer spatial and temporal resolution of Na+. It does this effectively even in the presence of normal levels of other ions in the body. Additionally, SBFI requires only a small cell sample, permits the visualization of indicator compartmentalization, and can differentiate against dye leakes from cells. The most widely used technique for measuring intracellular sodium concentration (Na+) involves the use of fluorescent microscopy (utilized with SBFI). Fluorescent microscopy is necessary to switch between filters.

SBFI is a chemical compound utilized in biology as a fluorescent signal for detecting intracellular sodium ions. It is a ratiometric dye, and can be excited at 2 different wavelengths (340 and 380 nm). Upon Na+ binding to SBFI, the fluorescence excitation/emission ratio is 340/505 nm when measuring Na+ bound SBFI and 380/505 nm when measuring Na+ free SBFI. The ratio of emitted fluorescence at specific wavelengths (340 and 380) is directly correlated with the intracellular sodium concentration when using SBFI. In contrast, the emission remains constant (505 nm) regardless of the changes in sodium concentration.