Figure 5.

Absorption spectra of chromogenic substrate S, X-Gluc (X-Gluc, dash, orange; for chemical structure, see Figure 1, in PBS, extinction coefficient ($\epsilon$) of indigo in dimethyl sulfoxide (DMSO) (SO, solid, black) and pyridine (Py, dash dot, magenta) at 25 °C. The maxima of indigo in DMSO are located as ${\epsilon }_{max}$ = 19,600 and 28,500 M⁻¹cm⁻¹ at 619.6 and 289.0 nm, respectively, while the maximum of indigo in pyridine is found as ${\epsilon }_{max}$ = 18,800 M⁻¹cm⁻¹ at 611.7 nm. The centers of red-green-blue (RGB) bands [35] are indicated with the vertical lines.