We investigated the UV–vis absorption and fluorescence emission spectra of IDNA in the presence and absence of H
2S. As shown in
Fig. 1a, In the mixed solution of IDNA (10 μmol/L) in DMSO and H
2O (v/v, 4:6), 0–1 mmol/L Na
2S (the H
2S donor) was gradually added, after 30 min of response, the absorption band at 550 nm was significantly decreased, accompanied by the absorption band at 475 nm was highlighted. Correspondingly, as the concentration of H
2S increased, the color of IDNA was noticed to change from purple to light yellow under naked eyes (
Fig. 1e). When the concentration of H
2S was in the range of 0.3–0.5 mmol/L, the absorption spectrum showed a good linear relationship,
R2=0.9978 (
Fig. 1b).
Fig. 1c indicated the fluorescence emission spectrum of IDNA (10 μmol/L). The addition of H
2S resulted a decrease in the peak at 620 nm and an increase in the peak at 510 nm, and when the concentration of H
2S reached 1 mmol/L, the peak at 510 nm increased to saturation. Therefore, the fluorescence intensity ratio (
I510/
I620) was used as a monitor for H
2S. The signal of the IDNA exhibited a good linear relationship when the concentration of H
2S was 0.3–0.47 mmol/L, while exhibiting a high sensitivity to H
2S at a low detection limit of 7 μmol/L (
Fig. 1d) [
36]. The change in fluorescence color under the 365 nm portable UV lamp, from pink to green, could be obtained from
Fig. 1f. As indicated in Fig. S1 (Supporting information), IDNA had good photostability within 15 min, if the irradiation time lasted longer, the photosability was not satisfactory. Meanwhile using fluorescein (quantum yield
Φs=79%) as a standard reference (dissolved in 0.1 mol/L NaOH), the fluorescence quantum yield of IDNA (
Φx) was measured to be about 8% [
37]. All these spectral results provided a theoretical basis for IDNA as a ratiometric fluorescent probe for highly sensitive monitoring of H
2S.