Notes: Laurdan is a membrane-permeable fluorescent probe that displays spectral sensitivity to the phospholipid phase of the cell membrane to which it is bound.{37064} Quantitation of generalized polarization (GP) of laurdan can be used to identify phospholipid phase. When excited at 340 nm, GP values are 0.6 and -0.2 for gel phase and liquid crystalline phase, respectively. GP does not change with polar head group or pH (in the range 4-10); it changes only with phase state.