Fig. 4: Sensitivity investigations.

a Fluorescence emission spectra of TFPT-BTAN-AO upon gradual addition of UO22+ (λex = 277 nm). Inset photos show the fluorescence emission change (under a 365 nm UV lamp) of TFPT-BTAN-AO after addition of UO22+. b Fluorescence intensity at 460 nm versus the concentration of UO22+. Inset: The linear calibration plot for UO22+ detection. Error bars represent S.D. n = 3 independent experiments.