Fig. 1. Chemical structures of DNP-based fluorescent probes for H₂S

Fig. 2. Chemical structures of NBD-based fluorescent probes for H₂S

Fig. 3. Chemical structures of DNBS-based fluorescent probes for H₂S

Fig. 4. Chemical structures of other H₂S fluorescent probes based on nucleophilic attack

Fig. 5. Chemical structures of H₂S fluorescent probes based on azide reduction(a, b, c)

Fig. 6. Chemical structures of H₂S fluorescent probes based on reduction of nitro groups to amines (a, b)

Fig. 7. Chemical structures of H₂S fluorescent probes based on disulfide exchange (a and b) and addition reaction (c and d)

Fig. 8. Schematic illustration of nanoprobe (NPs@BOD/CPT) for H₂S^[28]

Fig. 9. Schematic illustration of nanoprobe (TPAMC-UCNPs@PEG) for H₂S^[28]

Fig. 10. Schematic illustration of nanoprobe (1²⁺-SNPs) for H₂S^[29]

Fig. 11. Schematic illustration of multi-wavelength nanoprobe for H₂S^[30]

Fig. 12. Schematic illustration of the synthesis procedure of Ag-CEW nanoprobe and endogenous H₂S-triggered highly specific visualization of colon cancer^[31]