Chulhun Kang

Hydrogen sulfide (H₂S) acts as a crucial biological and environmental component in a variety of processes. Abnormal levels of H₂S endogenously generated in human body are associated with various diseases. Meanwhile, H₂S gas leaked from various manufacturing environments has a fatal effect against the human body. For this reason, H₂S has been considered as a potential biomarker for the diagnosis and treatment of various human diseases, and as a toxic gas that should be detected when leaked to the workplace for the safety of workers. In this study, we synthesized an azide‐containing naphthalimide derivative that can play as a fluorescence turn‐on probe for H₂S.

An indole-based fluorescent chemosensor was developed for the selective imaging of autophagosomes in live cells. It appears as puncta in the fluorescence confocal images and co-localizes with autophagosomes.

The conjugation site of dihydrofluorescein (H₂F) is important for the rational design of H₂F-based reactive oxygen species (ROS) sensors. Despite the prevalence of H₂F analogs detecting cellular ROS, the role of the carboxylic acid of H₂F in oxidation is still unclear. To get insight into the conjugation site of H₂F, we synthesized H₂F diacetate (2) and its amide derivative (3). The absorption and emission spectra of deacetylated 2 and 3 in the presence of H₂O₂/hematin showed that the carboxylic acid of H₂F plays a crucial role in the oxidation of H₂F. NMR and HPLC analysis of the oxidation product of deacetylated 3 showed a quantitative and fast generation of non-fluorescent spirolactam (F-Lactam). As regards these observations, we untouched the carboxylic acid at the 3rd position and designed an H₂F-based ROS sensor (7) that conjugated the lipophilic chain at the 5th position instead. A series of confocal microscopic experiments of 7 demonstrated that 7 prefers the ER location and that ROS are elevated in the cells by ER stress inducers.

Endoplasmic reticulum (ER) has a unique redox environment, which plays critical roles in the organelle's function and in its pathological responses such as ER stress. In this work, we introduce an ER‐targeting fluorogenic reactive oxygen species (ROS) chemosensor (ER‐Flu) from copper(I)‐catalyzed alkyne‐azide cycloaddition of 3‐propargyl ester of 2′,7′‐dichlorodihydrofluorescein diacetate and N₃‐glibenclamide, which were adopted as a fluorogenic ROS sensing module and an ER‐targeting module, respectively. Thereby, a series of confocal microscopic experiments of ER‐Flu demonstrated that the sensor localizes in ER of the live cells and that ROS are elevated in the cells by ER stress inducers such as thapsigargin, brefeldin A, and tunicamycin.

The emergence of novel two-dimensional (2D) monoelemental materials (Xenes) has shown remarkable potential for their applications in different fields of technology, as well as addressing new discoveries in fundamental science. Xenes (e.g., borophene, silicene, germanene, stanene, phosphorene, arsenene, antimonene, bismuthene, and tellurene) are of particular interest because they are the most chemically tractable materials for synthetic exploration. Owing to their excellent physical, chemical, electronic and optical properties, Xenes have been regarded as promising agents for biosensors, bioimaging, therapeutic delivery, and theranostics, as well as in several other new bio-applications. In this tutorial review, we summarize their general properties including the classification of Xenes according to their bulk properties. The synthetic and modification methods of Xenes are also presented. Furthermore, the representative Xene nanoplatforms for various biomedical applications are highlighted. Finally, research progress, challenges, and perspectives for the future development of Xenes in biomedicines are discussed.

We developed a disulfide-conjugated aggregation-induced emission luminogens (AIEgen) (1) that can dramatically enhance the aggregability through a H₂S-selective disulfide cleavage and its dimerization. Probe 1 was composed of tetraphenylethene (TPE) as an AIEgen and disulfide bond as a reaction site for H₂S. Under physiological conditions, probe 1 can provide strong fluorescence at 480 nm in response to H₂S through the formation of TPE dimer (2). This fluorogenic reaction was highly selective for H₂S over other potential interferants, such as biologically abundant thiols (e.g., glutathione, homocysteine, cysteine), reactive oxygen species, metal ions, and anions. In addition, probe 1 showed fluorescence change in the presence of H₂S in the pH range of 5–8. The limit of detection for H₂S was estimated to be 84 nM, which was a significant value at physiological H₂S level. Moreover, probe 1 fluorescently imaged even the endogenous H₂S, confirmed by the inhibition of H₂S-related enzymes (cystathionine β-synthase/cystathionine γ-lyase) in live cells. Additionally, we demonstrated the simple and rapid detection of gaseous H₂S using 1-coated thin-layer chromatography plate.

We developed a fluorescent pH probe (1) capable of two-photon excitation and far-visible-emission based on FRET, composed of naphthalimide–piperazine–rhodamine. It exhibited a pH-dependent reversible and fast ratiometric fluorescence change in the rhodamine emission. Probe 1 was applied to image the pH perturbations of mitochondria in living cells and tissues.

Herein, we explore glycyrrhetinic acid (GA) as an active targeting ligand for hepatocellular carcinoma (HCC) using a small molecule approach.

We synthesized a fluorogenic disulfide-based naphthalimide thiol probe (ER-Naph) with a hydrophilic endoplasmic reticulum (ER)-guiding glibenclamide unit. Its ER targeting ability and high selectivity to GSH over thioredoxin, a potent competitor, were clearly demonstrated, both in solution and in vitro. Finally, a confocal microscopic investigation revealed that GSH levels in the ER were dramatically decreased under thapsigargin, brefeldin A, and tunicamycin-induced ER stress models.