What are the commonly used Na+ indicators?

Commonly used Na+ indicators include: SBFI, Sodium Green indicators, Asante Sodium Green, and CoroNa Green. 

1. SBFI is a membrane-permeant, ratiometric green fluorescent indicator dye. The most widely used technique for measuring intracellular sodium concentration (Na+) involves the use of fluorescent microscopy (utilized with SBFI). This dye has a Kd value of 20 for Na+ concentration. 
2. Sodium Green indicators are excited at 488 nm, and can be used with flow cytometers as well as confocal laser-scanning microscopes. This indicator is made up of two 2,7-dichlorofluorescin dyes connected to nitrogen molecules of a crown ether. The crown ether has a unique size which permits it to selectively bind with Na+ ions. When the Sodium Green indicator binds to Na+, it displays an increase in fluorescence emission intensity without a significant change in wavelength. In comparison to SBFI, this indicator exhibits higher selectivity for Na+ than K+ (41 times greater), and has a greater fluorescence quantum yield (0.2 compared to 0.08 in SBFI) for Na+ solutions. The Kd value of Sodium Green indicator for Na+ is 6 mM at 22°C (in K+ free solution) and 21 mM at 22°C in solutions with Na+ and K+ (at an ion concentration of 135 mM). 
3. Corona Green is a green fluorescent Na+ indicator which displays an increase in fluorescence intensity as it binds to Na+. It has an fluorescence excitation/emission ratio of 492/516 nm. The CoroNa Green indicator (MW 586) is less than half the size of Sodium Green (MW 1668), and consists of a fluorescein molecule bound to a crown ether. This smaller size makes the dye more effective in loading cells compared to the larger Sodium Green tetraacetate. 
4. Asante Sodium Green indicator is another Na+ indicator, with a fluorescence excitation/emission ratio of 517/540 nm. It is also able to be excited at a wavelength of 488 nm. This dye offers cytosolic fluorescence and signal stability (as there is no dye loss or bleaching) for longer than 1 hour at 37°C.