What is Sodium-binding benzofuran isophthalate (SBFI)?

SBFI is a chemical compound utilized in biology as a fluorescent signal for detecting intracellular sodium ions. More specifically, SBFI is a membrane-permeant, ratiometric green fluorescent indicator dye. This dye has a Kd value of 20 for Na+ concentration and UV light is required for excitation. The most widely used technique for measuring intracellular sodium concentration (Na+) involves the use of fluorescent microscopy (utilized with SBFI). Rising levels of sodium ions increases the efficiency of excitation at specific wavelengths (330-345 nm) to a higher range (370-390 nm). This process is observed when measuring emitted light between 450-550 nm. The fluorescence excitation/emission ratio is 340/505 nm when measuring Na+ bound SBFI and 380/505 nm when measuring Na+ free SBFI. It is important to note that SBFI can also detect K+ levels, however, it is 18 times more selective for Na+ than K+.