FAST & splitFAST applications in live-cell imaging

Why a fluorogenic tag opens new experiments

Every fluorescent protein in the GFP lineage has to fold and then chemically mature its own chromophore — a slow, one-way reaction that consumes molecular oxygen. That single requirement is behind three familiar frustrations: a maturation lag before anything is visible, a signal that cannot be switched off, and darkness in anaerobic or hypoxic samples. FAST removes all three. Its fluorogen binds in seconds, releases just as readily, and needs no oxygen at any step — and because the fluorogen is dark until it is bound, background stays low without a wash step. The tag is also small enough (14 kDa) to sit on sensitive fusion partners without disturbing them.

Applications at a glance

Oxygen-independent imaging of anaerobes — image obligate anaerobes such as Clostridium, hypoxic tissue and living multi-species biofilms in real time, where GFP and mCherry go dark.

Detecting protein–protein interactions — splitFAST reports interactions the moment they form and the moment they break, making it a genuinely dynamic, reversible interaction sensor rather than a one-shot readout.

Protein & cell labeling — a compact, bright general-purpose tag for tracking protein localisation and identifying cells, at the bench or in flow.

One tag, many colours — a single genetic construct spans green to near-infrared simply by changing which fluorogen you add, with no re-cloning.

Reversible labeling, silent tag — wash the fluorogen out to silence the signal, add it back to restore it; label transiently without permanently marking a line.

Choosing the right fluorogen

FAST is one tag; the colour and the behaviour come from the fluorogen you pair with it. Cell-permeant fluorogens run from tfLime (green) through tfAmber, tfCoral and tfPoppy (far-red) to tfCarmine in the near-infrared. Non-permeant fluorogens — tfAmber-NP and tfFox-NP — stay outside the cell and label only surface-exposed FAST. Browse the full range on the products page.

Frequently asked

How is FAST different from GFP?

GFP builds and matures its own chromophore in an oxygen-dependent reaction, so it is slow to appear, permanent once formed, and dark without oxygen. FAST lights up a small fluorogen on contact — instantly, reversibly and independently of oxygen — and changes colour when you change the fluorogen.

Do I need special equipment?

No. Any fluorescence microscope, flow cytometer or microplate reader with standard filters will do; the fluorogen is simply added to the culture medium.