When the Nobel Prize for Chemistry was awarded to Osamu Shimomura, Martin Chalfie, and Roger Y. Tsien for the discovery and development of the green fluorescent protein (GFP) in 2008, researchers around the world were already using GFP (and the many other variants) in a wide range of cell-based assays.
One of the most important uses for GFP is monitoring a variety of cellular processes in real-time. The many applications that use fluorescent proteins include: intracellular transport, protein signaling, receptor desensitization, cell movement, migration, division, apoptosis, metabolism, differentiation, chemotaxis, transcription, translation, and many more.
As with any new, popular, Nobel Prize-winning research advancement, a correlative advancement usually occurs in analytical instrumentation. One instrument that all life science laboratories have access to because of the GFP discovery is the confocal microscope. Live, real-time pictures (and movies) of cellular processes, highlighted by different fluorescent proteins, are easily recorded using a confocal microscope.
Confocal microscopes have allowed researchers to obtain fantastic snapshots of biological processes using fluorescent proteins. One drawback of confocal microscopy, though, is that patience and time are needed to obtain reliable, reproducible data since only one cell or cell cluster is viewed at a time.
Another instrument that has increased in utility due to the GFP discovery is the flow cytometer. More specifically, specialized types of flow cytometers can perform Fluorescence-Activated Cell Sorting (FACS®), which is often used in high-throughput screening (HTS) and high-content screening (HCS) labs. FACS provides a way to sort heterogeneous cell populations into homogeneous subgroups, thereby counting and separating the cells that have a fluorescent protein from those that do not.
FACS lack one of the limitations of confocal microscopy in that it provides an automated method that counts one specific activated cell type. But like the confocal microscope, flow cytometers that perform FACS are still limited by the time it can take to obtain data from an experiment with many testable parameters. Hours can pass during a FACS experiment, which means that assay conditions may not be uniform across the entire test.
The fluorescent microplate reader is another instrument that has seen an expanded role in life science laboratories after the discovery of GFP. Used mainly in life science or HTS laboratories to study simple, homogeneous absorbance, luminescence, or fluorescence based experiments, microplate readers have evolved into multifunction instruments that can perform complex, heterogeneous cell-based assays. Being able to measure mL to nL volumes, and up to thousands of samples at once, microplate readers allow for all types of reproducible, cell-based assays to be measured in only minutes.
Until recently, though, there was a limitation to cell-based experiments performed in a microplate reader in that the same sensitivity obtained on a confocal microscope or a FACS could not be matched by a microplate reader. For live, real-time cell-based experiments, it is preferable to read from the bottom of the microplate.