What are Suitable Criteria for a Polarization Standard?
Many have used and are using Raleigh scatters as standards for instrument calibration as the polarization of scattered light is 1,00. Such scatters include e.g. glycogen and colloidal silica. Some fluorophores that have been used as polarization standards are e.g. fluorescein but its relatively long fluorescence lifetime of 4 ns and its fast rotational correlation time of about 100 ps yields only a low polarization value of 0.023 in solution. This value is too low to be measured with high precision. Thompson and Gryczynski were proposing Ru(bpy)3 as a better standard because it has a very long lifetime and a zero anisotropy throughout its excitation spectrum [1]. Obviously the best candidate for a polarization standard is a fluorescent probe with a short lifetime in solution at room temperature for it to exhibit a reasonably high polarization. There are several dyes commercially available that have lifetimes in the low picosecond range. Rose Bengal (Sigma-Aldrich 330000), Erythrosin B
