Visualization of exhaled hydrogen sulphide on test paper with an ultrasensitive and time-gated luminescent probe

Abstract

Luminescent chemosensors for hydrogen sulphide (H₂S) are of great interest because of the close association of H₂S with our health. However, current probes for H₂S detection have problems such as low sensitivity/selectivity, poor aqueous-solubility or interference from background fluorescence. This study reports an ultrasensitive and time-gated “switch on” probe for detection of H₂S, and its application in test paper for visualization of exhaled H₂S. The complex probe is synthesized with a luminescent Tb³⁺ centre and three ligands of azido (–N₃) substituted pyridine-2,6-dicarboxylic acid, giving the probe high hydrophilicity and relatively fast reaction dynamics with H₂S because there are three –N₃ groups in each molecule. The introduced –N₃ group as a strong electron-withdrawing moiety effectively changes the energy level of ligand via intramolecular charge transfer (ICT), and thus breaks the energy transferring from ligand to lanthanide ion, resulting in quenching of Tb³⁺ luminescence. On addition of H₂S, the –N₃ group can be reduced to an amine group to break the process of ICT, and the luminescence of Tb³⁺ is recovered at a nanomolar sensitivity level. With a long lifetime of luminescence of Tb³⁺ centre (1.9 ms), use of a time-gated technique effectively eliminates the background fluorescence by delaying fluorescence collection for 0.1 ms. The test paper imprinted by the complex probe ink can visualize clearly the trace H₂S gas exhaled by mice.