Fura-2

• Is a second-generation, UV light-excitable, ratiometric indicator dye
• Widely used for ratio-imaging microscopy
• Enables researchers to accurately measure intracellular Ca2+ in living cells
• Ratiometric readout minimizes problems associated with varying cell thicknesses, dye leakage, photobleaching, and uneven dye loading
• Especially well-suited for ratio-imaging microscopy
• On binding with Ca2+ exhibits an absorption shift that can be observed by scanning the excitation spectrum between 300 and 400 nm, while monitoring the emission at ~510 nm

Quin-2

• Is a first-generation, membrane-impermeable fluorescent Ca2+ indicator
• Demonstrates strong affinity for calcium, resulting in notable shift in ultraviolet absorption and fluorescence spectra between the bound and unbound states
• Is sensitive enough to monitor low levels of calcium in resting cells.
• Not affected by intracellular pH, sodium gradients, or membrane potential range
• Has lower absorptivity and quantum yield values as compared to Fura-2
• Excitation and emission maxima are 339/492 nm, respectively.