Intensive searches for novel green fluorescent protein (GFP)-like fluorescent proteins have identified more than 150 distinct genes that, together with its mutants, cover the excitation range from 380 to 600 nanometers (nm) and the emission range from 440 to 650 nm (see table below). Despite spectral diversity, a family of GFP-like proteins possesses common significant structural, biochemical and photophysical features. Many of these spectroscopically active proteins are developed to commercially available genetically-encoded fluorescent probes. In comparison to other natural pigments and fluorophores, GFP-like proteins stand out because they form internal chromophores without requiring accessory cofactors, external enzymatic catalysis or substrates other than molecular oxygen. It gives GFP-like proteins many advantages including that chromophore formation is possible in live organisms, tissues or cells while maintaining their integrity as well as molecular, organelle and tissue targeting and specificity.

Fluorescent proteins can be divided into several fluorescent groups with respect to the appearance of the purified protein to the human eye:

• Blue (below 460 nm, BFP)
• Cyan (460-500 nm, CFP)
• Green (~500-520 nm, GFP)
• Yellow (~520-550 nm, YFP)
• Orange (~550-570 nm, OFP)
• Red (~570-620 nm, RFP)
• Far red (above 620 nm, FRFP)

In addition, several fluorescent proteins exhibit photoactivatable (PA-FP) or photoswitchable behavior and therefore are called photoactivatable (PA-FP) or photoswitchable (PS-FP) fluorescent proteins, respectively. These proteins are originally either dark (PA-FP) or fluoresce at one wavelength (PS-FP) but become fluorescent or fluorescent at a distinct wavelength, respectively, upon irradiation with an intense violet or blue light. Developmental research efforts are ongoing to improve the brightness and stability of fluorescent proteins, thus improving their overall usefulness. Flow cytometers currently available at the core facility allow for simultaneous detection of many fluorescent proteins of different fluorescent groups simultaneously expressed in the cells.

The following list is not exhaustive. It illustrates the properties of recommended fluorescent proteins that were available at the time that the table was last updated, which happens regularly.

Recommended for Flow Cytometry Fluorescent Proteins