Fluorescent paper sensor fabricated by carbazole-based probes for dual visual detection of Cu2+ and gaseous H2S

Abstract

We report a fluorescent carbazole-based probe to achieve visual detection of Cu²⁺ and gaseous H₂S with paper sensors in a fluorescent “on–off–on” mode. A common carbazole mother molecule is reconstructed by dual substitute and hydrazine reactions to obtain triple dentates to a single Cu²⁺ ion, and thus the fluorescence of the carbazole ring is strongly quenched by the captured Cu²⁺. Subsequently, the coordinative Cu²⁺ can be snatched by S²⁻ via the formation of CuS, leading to the recovery of carbazole fluorescence. The above reactions provide the sensitive and prompt detection of Cu²⁺ and S²⁻ with the limits of 65 nM and 0.29 μM, respectively. The reusability of the “on–off–on” fluorescent switch is well demonstrated by a recycling experiment with alternate additions of Cu²⁺ and S²⁻. Moreover, paper sensors are fabricated and used for the visual detection of Cu²⁺ and gaseous H₂S with the limits of 10⁻⁶ M and 15 ppm.