The February issue of Nature Biotechnology talks about the newly developed “fluorogen activating proteins” (FAPs) that will become a key component of novel molecular biosensor technology being created at Carnegie Mellon.  The FAP is a specialized single chain antibody (scFv), a recombinant fragment of full-size antibody proteins that the human immune system uses to identify intruders like bacteria or viruses.  These FAP can be used to monitor biological activities of individual proteins and other biomolecules within living cells in real time.  The FAPs are designed to emit fluorescent light only when bound to a fluorogen -malachite green and thiazole orange- an otherwise non-fluorescent dye added by the scientists. This feature will allow biologists to track proteins on the cell surface and within living cells in very simple and direct ways, eliminating cumbersome experimental steps.  Researchers say the fluorogen activating proteins are particularly useful for developing molecular biosensors, because FAPs allow researchers to not only see where the target protein is within the cell, but also detect color changes when it becomes fluorescent. Such color changes may reflect changes in the local environment of the protein, and allow quantitative sensing in real time of the biological activity of proteins and biomolecules that are in close proximity to each other.  Scientists also can design fluorogens that can enter the cell and fluorogens that can’t. When used with fluorogens that are excluded from the cell, the FAP technology provides an exceptionally selective biosensor for proteins at the outside of the cell surface.  The ultimate goal is to put molecular biosensors based on FAP technology inside cells.  Thus FAPs are the essential first step in developing molecular biosensors that will monitor dynamic changes occurring within cells