Fig. 1. Schematic of the probe structure.

Fig. 2. Schematic of the fluorescence detection of chloride ions by g-CNQDs.

Fig. 3. Schematic of the fiber probe preparation process.

Fig. 4. Schematic of experimental setup.

Fig. 5. (a) Different excitation wavelength fluorescence (FL) spectra. (b) Fluorescence spectra for g-CNQDs/Ag⁺ and g-CNQDs/Ag⁺ within hydrogel. (c) Normalized fluorescence spectra for g-CNQDs/Ag⁺ and g-CNQDs/Ag⁺ within hydrogel. (d) Absorption spectra for g-CNQDs, g-CNQDs/Ag⁺, and g-CNQDs/Ag⁺ within hydrogel.

Fig. 6. Fluorescence spectra of Ag⁺ added g-CNQDs.

Fig. 7. pH effect on the fluorescence intensity of the fiber probe.

Fig. 8. (a) Fluorescence spectra for optical fiber probes with different chloride ion concentrations. (b) Chloride ion linear fit of fluorescence intensity.

Fig. 9. Fluorescence intensity at different time.

Fig. 10. Fluorescence response to different anions.