( a ) Fluorescence emission spectra of TO-GMP (65 nM) in the presence of varying concentrations of GTP Class I (0, 0.0195, 0.039, 0.078, 0.1563, 0.625 and 2.5 µM, frssom bottom to top). The insert shows for maximum fluorescence versus aptamer concentration curve fitting ( K_d = 60 nM). ( b ) Dependence of the fluorescence on the concentration of GTP Class I aptamer for: 1 ; TO ; 2 and TO-C ₁₀ (all measurements at 50 nM of dyes).