A water-soluble near-infrared fluorescent probe for monitoring change of hydrogen sulfide during cell damage and repair process

Near-infrared fluorescent probe based on the regulatory dye pKa for imaging of H2S in rice roots and living cells

Hydrogen sulfide (H2S) is a key factor in various biological processes such as plant grow and its response to environmental stress. Here, we develop a novel near-infrared (NIR) fluorescent probe for detecting hydrogen sulfide based on the regulatory NIR dye pKa values. After triggering the H2S substitution response, probe A with introducing the cyano moiety not only exhibits a significant near-infrared emission (Emax: 724 nm) response in physiological environments, but also shows a fast response, high selectivity, and sensitivity (LOD as 0.52 µM). In addition, probe A with low biological cytotoxicity is successfully used for imaging detection of cellular exogenous and endogenous hydrogen sulfide. More importantly, in situ imaging of probe A tracks the H2S fluctuations in the rice root system and its response to environmental stress. Hence, this work offers a new NIR fluorescence imaging monitoring tool for hydrogen sulfide in biological systems.

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.

Small Molecule Optical Probes for Detection of H2S in Water Samples: A Review

Hydrogen sulfide (H2S) is closely linked to not only environmental hazards, but also it affects human health due to its toxic nature and the exposure risks associated with several occupational settings. Therefore, detection of this pollutant in water sources has garnered immense importance in the analytical research arena. Several research groups have devoted great efforts to explore the selective as well as sensitive methods to detect H2S concentrations in water. Recent studies describe different strategies for sensing this ubiquitous gas in real-life water samples. Though many of the designed and developed H2S detection approaches based on the use of organic small molecules facilitate qualitative/quantitative detection of the toxic contaminant in water, optical detection has been acknowledged as one of the best, attributed to the simple, highly sensitive, selective, and good repeatability features of the technique. Therefore, this review is an attempt to offer a general perspective of easy-to-use and fast response optical detection techniques for H2S, fluorimetry and colorimetry, over a wide variety of other instrumental platforms. The review affords a concise summary of the various design strategies adopted by various researchers in constructing small organic molecules as H2S sensors and offers insight into their mechanistic pathways. Moreover, it collates the salient aspects of optical detection techniques and highlights the future scope for prospective exploration in this field based on the limitations of the existing H2S probes.

A Novel DNBS-based Fluorescent Probe for the Detection of H2S in Cells and on Test Strips

Hydrogen sulfide (H2S) plays a key role in the physiology and pathology of organisms, and H2S in the environment is easily absorbed and harmful to health. It is of great significance to develop a probe with good selectivity, high sensitivity and good stability that can detect hydrogen sulfide inside and outside organisms. In this work, we designed a novel "turn-on" fluorescent probe CIM-SDB for the detection of H2S. The probe CIM-SDB used indene-carbazole as the fluorophore and 2,4-dinitrobenzenesulfonyl as the recognition site. The probe CIM-SDB exhibited high selectivity and sensitivity to H2S (detection limit as low as 123 nM). Moreover, the probe CIM-SDB was successfully applied to the detection of intracellular exogenous and endogenous H2S, and the test strips prepared by the probe CIM-SDB could realize the convenient and rapid detection of H2S.

A self-immolative near-infrared fluorescent probe for identification of cancer cells and facilitating its apoptosis

Hydrogen sulfide (H2S) plays a significant role in the onset and progression of cancer. It has led to increased interest in its potential as a diagnostic tool owing to its overexpression in cancer. However, research into the anti-cancer activity of H2S, particularly its ability to promote apoptosis, is hindered by the lack of effective detection tools. To gain a comprehensive understanding of the targeted efficacy of H2S in promoting cancer cell apoptosis, we designed and synthesized a self-immolative near-infrared fluorescent diagnostic probe, named YH-NO2. The activation of this self-immolative reaction is dependent on the presence of nitroreductase (NTR) overexpressed in tumor cells. The design of YH-NO2 involves releasing fluorophores through the activated self-immolative reaction for detection, while simultaneously releasing H2S-loaded self-immolative spacers to promote cancer cell apoptosis. Consequently, YH-NO2 achieves a seamless integration of recognizing and promoting cancer cell apoptosis through its self-immolative structure. This dual function allows YH-NO2 to recognize NTR activity in cells under varying hypoxia levels and differentiate between normal cells and cancer cells using imaging technology. Notably, YH-NO2 exhibits remarkable stability in cellular environments, providing controlled and selective H2S release, thereby targeting the elimination of cancer cells through the promotion of apoptosis. Furthermore, in vivo experiments have demonstrated that YH-NO2 can accurately identify tumor tissue and effectively reduce its size by utilizing its apoptosis-promoting properties. These findings not only provide further evidence for the anti-cancer activity of H2S but also offer valuable tools for understanding the complex relationship between H2S and cancer.

A highly selective and sensitive fluorescence probe based on BODIPY-cyclen for hydrogen sulfide detection in living cells and serum

Hydrogen sulfide (H2S) is a multifunctional gaseous signaling molecule that plays a vital role in several biological processes. In the present study, a BODIPY-based fluorescent probe called 8-[4-((1,4,7,10-tetraazacyclododecane)methyl)phenyl]-4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a, 4a-diaza-s-indacene (BA-Cyclen)-Cu was designed and synthesized; this probe is a Cu(Ⅱ) complex that uses Cu(Ⅱ) decomplexation to achieve the sensitive and rapid detection of aqueous H2S via the "turn-on" mode. We observed that BA-Cyclen-Cu exhibited good membrane permeability, low toxicity, and lysosome-targeting ability, facilitating H2S detection in living cells. Furthermore, we demonstrated the potential biological applications of the probe by measuring exogenous H2S originating from Na2S and GYY4137, a slow-release donor, and endogenous H2S generated via the catalysis of cystathionine-β-synthase in both normal (H9c2) and cancerous (U87) cells. Moreover, BA-Cyclen-Cu was successfully used to detect exogenous H2S by the external standard method in fetal bovine serum, the serum of a healthy person, and the serum of a patient with liver cancer.

A novel polymer-based probe for fluorescently ratiometric sensing of hydrogen sulfide with multiple applications

Hydrogen sulfide (H2S) as an endogenous signaling molecule, plays an irreplaceable role in many important physiological activities. It is also closely related to sewage treatment, wine quality evaluation, and food spoilage. Herein, we have successfully synthesized a novel polymer-based probe P1 for fluorescently ratiometric sensing of H2S with a high selectivity and sensitivity. By virtue of ring-opening metathesis polymerization (ROMP), P1 was prepared with the disulfide bond linked coumarin-norbornene dyad NB-SS-COU as energy donor, the aggregation-induced emission (AIE) fluorophore anchored norbornene NB-TPE as energy receptor, and the polyethylene glycol (PEG) attached norbornene NB-PEG as a hydrophilic chain. At the 400 nm excitation, P1 displays a bright red emission at 615 nm due to the efficient fluorescence resonance energy transfer (FRET) from energy donor COU to energy acceptor TPE. Upon addition of H2S, it shows strong COU-based blue emission at 473 nm for cleavage of the disulfide bond. We also constructed a smartphone sensing platform to conduct visual quantitative detection of H2S by calculating the B/R (blue/red) emission ratio values. Moreover, P1 can be successfully employed in evaluating the level fluctuations of endogenous and exogenous H2S in living cells, testing water samples/wine samples, and monitoring food freshness.

Design strategy for an analyte-compensated fluorescent probe to reduce its toxicity

During biological detection, the toxicity caused by probes to living organisms is neglected. In this study, an analyte-compensated fluorescent probe (NP-SN₃) was constructed for the detection of H₂S. Through experiments with HepG2 cells and zebrafish embryos and larvae, the NP-SN₃ probe showed no significant difference in imaging performance compared with the traditional probe (NP-N₃) but exhibited lower detection-induced toxicity in the imaging of liver fibrosis in activated HSC-T6 cells. During the development of zebrafish embryos and continuous administration in rats, NP-SN₃ showed a lower death rate, higher hatchability and lower malformation in zebrafish embryos and milder pathological symptoms in stained rat tissues.