AkaLumine, an open-ring analog of CycLuc1, is a novel luciferin analog and substrate for firefly luciferase. The bioluminescence produced by AkaLumine in reactions with native firefly luciferase is in the near-infrared wavelength ranges (λmax=677 nm), and yields significantly increased target-detection sensitivity from deep tissues with maximal signals attained at very low concentrations, as compared with D-luciferin and emerging synthetic luciferin CycLuc1.