Activity-Based Fluorescent Probes for Hydrogen Sulfide and Related Reactive Sulfur Species

Hydrogen sulfide (H2S) is not only a well-established toxic gas but also an important small molecule bioregulator in all kingdoms of life. In contemporary biology, H2S is often classified as a "gasotransmitter," meaning that it is an endogenously produced membrane permeable gas that carries out essential cellular processes. Fluorescent probes for H2S and related reactive sulfur species (RSS) detection provide an important cornerstone for investigating the multifaceted roles of these important small molecules in complex biological systems. A now common approach to develop such tools is to develop "activity-based probes" that couple a specific H2S-mediated chemical reaction to a fluorescent output. This Review covers the different types of such probes and also highlights the chemical mechanisms by which each probe type is activated by specific RSS. Common examples include reduction of oxidized nitrogen motifs, disulfide exchange, electrophilic reactions, metal precipitation, and metal coordination. In addition, we also outline complementary activity-based probes for imaging reductant-labile and sulfane sulfur species, including persulfides and polysulfides. For probes highlighted in this Review, we focus on small molecule systems with demonstrated compatibility in cellular systems or related applications. Building from breadth of reported activity-based strategies and application, we also highlight key unmet challenges and future opportunities for advancing activity-based probes for H2S and related RSS.

A "double-locked" probe for the detection of hydrogen sulfide in a viscous system

A novel "double-locked" probe, DCO-H2S-V, was prepared for detecting hydrogen sulfide in a highly viscous system. Experiments demonstrated that only when H2S and a high viscosity environment coexist in a cell, can the probe be activated effectively and emit fluorescence. This has been successfully used for detecting the changes in viscosity and H2S in a Parkinson's disease model, PC-12 cells treated with glutamate.

A phenanthrene[9,10-d]imidazole-phenol-based fluorescent probe combining ESIPT and AIE for the “turn-on” detection of Cu2+ with green-emission and improved Stokes’ shift, and its application

The “turn-on” probe PIA(OH)-Py responds to Cu2+ in living cells and can determine the concentration of Cu2+ in blood samples.

A FRET-based upconversion nanoprobe assembled with an electrochromic chromophore for sensitive detection of hydrogen sulfide in vitro and in vivo

Hydrogen sulfide (H2S) as an important gaseous signaling molecule is closely related to numerous biological processes in living systems. To further study the physiological and pathological roles of H2S, convenient and efficient detection techniques for endogenous H2S in vivo are still in urgent demand. In this study, an electrochromic chromophore, dicationic 1,1,4,4-tetra-aryl butadiene (EM1), was innovatively introduced into upconversion nanoparticles (UCNPs) and a nanoprobe, PAAO-UCNPs-EM1, was constructed for the detection of H2S. This nanosystem was made of core-shell upconversion nanoparticles (NaYF4:Yb,Tm@NaYF4:Yb,Er), EM1, and polyacrylic acid (PAA)-octylamine. The EM1 with strong absorption ranging from 500 to 850 nm could serve as an energy acceptor to quench the upconversion luminescence of UCNPs through the Förster resonance energy transfer (FRET) process. In the presence of H2S, the EM1 in the nanoprobe was reduced to a colorless diene (EM2), resulting in the linear enhancement of luminescence emissions at 660 nm and 800 nm under the excitation of 980 nm light because the FRET was switched off. The nanoprobe PAAO-UCNPs-EM1PAAO-UCNPs-EM1 exhibited fast response and high sensitivity to H2S with a LoD of 1.21 × 10-7 M. Moreover, it was successfully employed in detecting the endogenous and exogenous H2S in living cells with high selectivity and low cytotoxicity. Also, this nanoprobe could distinguish normal and tumor cells by an upconversion luminescence imaging of endogenous H2S. Furthermore, the nanoprobe could significantly monitor H2S in a tumor-bearing nude mouse model. Therefore, we anticipate that this novel nanoprobe assembled with an electrochromic chromophore for responding to H2S and for bioimaging this molecule would have a promising prospect in biological and clinical investigations.