Calcium imaging. (A) The fluorescence spectra of the calcium-binding dye Fura-2 can be used to measure available calcium ion concentrations in solution and in cells. (B) A series of images show Ca2+ spreading across an egg cell following fertilization by sperm. These images were obtained through the use of Fura-2. The images are false colored: orange represents high Ca2+ concentrations, and green represents low Ca2+ concentrations.
[(A) Information from S. J. Lippard and J. M. Berg, Principles of Bioinorganic Chemistry (University Science Books, 1994), p. 193; (B) data from Carroll M. et al., J. Cell Sci. 116: 4997–5004, 2003.]