Optical properties of LucRB. a, Photographs of RLuc8.6 (I, ii) and LucRB (iii, iv) solutions in cuvettes. left (I, iii): under room light, right (ii, iv): BL in dark. For 10 μg of CTZ each, the total emitted BL emitted energy from RLuc8.6 (1.5 μM) and LucRB solutions (0.4 μM; same number of RLuc8.6) were estimated to be 50 μJ and 5.8 μJ, respectively. b, BL emission decay rates and total fluence of LucRB and RLuc8.6 as a function of concentration in PBS buffer (pH7.4). c, Normalized absorption (magenta), FL (orange) and BL (cyan) spectra of RB and RLuc8.6. d, Normalized BL of LucRB (B) and Luc8.6 (A), and the difference (B-A). Inset shows that the difference (magenta dotted line) coincides with the FL spectrum (orange) of LucRB.