The Nano-Glo HiBiT Extracellular Detection System quantitates cell surface or secreted protein expression in minutes using a simple add-mix-read assay format. Using the nonlytic Nano-Glo HiBiT Extracellular Detection Reagent, any proteins that are tagged with the 11 amino acid HiBiT peptide and expressed outside of the cell can be specifically quantitated. The detection reagent contains the complementary polypeptide LgBiT, which spontaneously interacts with the HiBiT tag to reconstitute the bright, luminescent NanoBiT enzyme. Luminescence is proportional to the amount of HiBiT-tagged protein present outside of the cell over seven orders of magnitude.