Ternary complexation mediated direct detection system for the vascular endothelial growth factor (VEGF). a) A schematic of the VEGF assay is shown, where domain 2 of Flt-1 (red and blue) is attached to both the N- and C-terminal halves of luciferase to directly detect the VEGF homodimer. b) Luminescence from reassembled luciferase in the presence and absence of VEGF, total assay time of 2.5 h starting from mRNA. A >13-fold increase in luminescence is observed in the presence of 15 nM VEGF dimer. c) A titration of VEGF dimer was performed, resulting in a linear relationship to luminescence output. d) A titration of free Flt-1 was used to compete with luciferase reassembly, resulting in an IC50 of 56 ± 8 nM. ALU, arbitrary luminescence units.