Rapid and selective visualization of mitochondrial hypochlorite by a red region water-soluble fluorescence probe

Water-Soluble Small Organic Fluorophores for Oncological Theragnostic Applications: Progress and Development

Cancer is one of the major noncommunicable diseases, responsible for millions of deaths every year worldwide. Though various cancer detection and treatment modalities are available today, many deaths occur owing to its late-stage detection and metastatic nature. Noninvasive detection using luminescence-based imaging tools is considered one of the promising techniques owing to its low cost, high sensitivity, and brightness. Moreover, these tools are unique and valuable as they can detect even the slightest changes in the cellular microenvironment. To achieve this, a fluorescent probe with strong tumor uptake and high spatial and temporal resolution, especially with high water solubility, is highly demanded. Recently, several water-soluble molecules with emission windows in the visible (400-700 nm), first near-infrared (NIR-I, 700-1000 nm), and second near-infrared (NIR-II, 1000-1700 nm) windows have been reported in literature. This review highlights recently reported water-soluble small organic fluorophores/dyes with applications in cancer diagnosis and therapeutics. We systematically highlight and describe the key concepts, structural classes of fluorophores, strategies for imparting water solubility, and applications in cancer therapy and diagnosis, i.e., theragnostics. We discuss examples of water-soluble fluorescent probes based on coumarin, xanthene, boron-dipyrromethene (BODIPY), and cyanine cores. Some other emerging classes of dyes based on carbocyclic and heterocyclic cores are also discussed. Besides, emerging molecular engineering methods to obtain such fluorophores are discussed. Finally, the opportunities and challenges in this research area are also delineated.

A zeolitic imidazolate framework-90-based probe for fluorescent detection of mitochondrial hypochlorite in living cells and zebrafish

An inorganic-organic hybrid probe MP-ZIF-90 was synthesized via a simple condensation reaction based on the free CHO groups of zeolitic imidazolate framework-90 (ZIF-90) and 4-methyl-1-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)pyridinium bromide (MP). This probe exhibited intense green emission, which was selectively quenched by the addition of ClO- anions. The response of probe MP-ZIF-90 toward ClO- was rapid (within 20 s) and sensitive, with a limit of detection (LOD) of 0.612 μM. Importantly, the utilization of the probe in the fluorescence imaging of ClO- anions in the mitochondria of living cells and zebrafish was demonstrated.

A novel AIRE-based fluorescent ratiometric probe with endoplasmic reticulum-targeting ability for detection of hypochlorite and bioimaging

Hypochlorite (ClO^-) plays an important role in the human immune defense system, but high concentrations of ClO^- in the endoplasmic reticulum (ER) damage cellular proteins, causing ER stress, cell death, and various diseases. Herein, we developed a simple hydrazone probe (1) featuring aggregation-induced ratiometric emission, which would quickly (within 20 s) and sensitively (detection limit of 15.4 μM) respond to ClO^- in an almost pure aqueous solution via a fluorescent ratiometric output. Furthermore, the probe was employed to track the level of ClO^- in the ER of HeLa cells and zebrafish.

Recent Advancements in the Design and Development of Near Infrared (NIR) Emitting Fluorescent Probes for Sensing and their Bio-Imaging Applications

Fluorescent bio-imaging will be the future in the medical diagnostic for visualising inner cellular and tissues. Near-infrared (NIR) emitting fluorescent probes serve dynamically for targeted fluorescent imaging of live cells and tissues. NIR imaging is advantageous because of its merits like deep tissue penetration, minimum damage to the tissue, reduced auto fluorescence from the background, and improved resolution in imaging. The Development of the NIR emitting probe was well explored recently and growing drastically. In this review, we summarise recent achievements in NIR probes in between 2018-2021. The merits and future applications have also been discussed in this review.

Advances in the Development of Water-Soluble Fluorogenic Probes for Bioimaging of Hypochlorite/Hypochlorous Acid in Cells and Organisms

This mini-review summarizes the development of intracellular fluorogenic probes for biological investigations of hypochlorous acid/hypochlorite (HOCl/OCl^-) in living cells and tissues. Monitoring the formation or effects of reactive oxygen species (ROS) inside living systems is critical in determining their roles in human physiology. HOCl/OCl^- is considered as an important member of the nonradical ROS family for its decisive microbicidal action in the innate immune system. Even though HOCl/OCl^- plays a defensive role in human health, abnormal or overexpression may have detrimental effects on the host physiology leading to many diseases, including neurodegeneration and cancer. In recent years, progress in the development of fluorescent imaging probes for observing HOCl/OCl^- levels in live cells and tissues has been made. Despite considerable advancement, challenges still exist in areas like working solvent/media, pH, response time, buffer selection, emission region, and others. In addition, this account aims to discuss the design strategies and sensing mechanisms of the representative fluorogenic probes for bioimaging of HOCl/OCl^-, endogenously and exogenously. Herein, we also have tried to provide the future direction to develop HOCl/OCl^- specific probes for disease diagnosis with particular attention to the requirement of the recognition group, solvent, and buffer media, which will be beneficial for those working in the domain of biomedical research.

A NIR fluorescent probe for the specific detection of hypochlorite and its application in vitro and in vivo

It is of great necessity to exploit a real-time, highly selective and sensitive method for hypochlorite (ClO^-) detection in both the environment and living systems because of the complex influence of ClO^- on health. In this paper, based on the intramolecular charge transfer (ICT) effect, a NIR fluorescent probe (probe DAB) was designed for the accurate detection of ClO^-, which produced a fluorescence response to ClO^- with high selectivity and rapid response (within 1 min). The probe DAB could determine ClO^- over the linear range of 0-80 μM with a low detection limit of 1.46 μM. And the sensing mechanism between the probe and ClO^- was verified using HPLC and MS. To further prove its practicability, the probe was applied for detecting ClO^- in actual water samples. In addition, owing to its good sensing properties and low cytotoxicity, probe DAB could be expediently applied to visualize ClO^- in living cells and zebrafish, and it is expected to be a useful tool for investigating the detailed functions and mechanisms of ClO^- in living systems.

A near-infrared fluorescent probe based on the hemicyanine skeleton for the detection of hydrogen peroxide in vivo

As a member of the reactive oxygen species, hydrogen peroxide (H₂O₂) plays critical roles in oxidative stress and cell signaling. Intracellular abnormal levels of H₂O₂ production are closely related to many diseases. Therefore, the real-time monitoring of H₂O₂ in the cells is important. In this work, we designed a novel fluorescent probe (Mito-H₂O₂) for the specific detection of H₂O₂ based on the hemicyanine skeleton, with bright near-infrared fluorescence emission. Mito-H₂O₂ displayed fast response, excellent water-solubility and great fluorescence intensity enhancement after the addition of H₂O₂. Furthermore, Mito-H₂O₂ has been successfully applied to image both of the exogenous and endogenous H₂O₂ in cells and mice with negligible cytotoxity.

Development of an ultrafast fluorescent probe for specific recognition of hypochlorous acid and its application in live cells

Hypochlorous acid (HOCl), a highly potent oxidant of reactive oxygen species, plays critical roles in many physiological and pathological processes. In this work, a novel coumarin-based fluorescent probe, Cou–HOCl, was prepared for the detection of HOCl. The probe exhibited good selectivity over other analytes, excellent sensitivity with a detection limit of 16 nM, and fast response within 5 s. And further study demonstrated that the probe could be used not only to image exogenous HOCl in various cells, but also to determine the fluctuating levels of HOCl in macrophage cells during inflammation.

Hypochlorous acid (HOCl), a highly potent oxidant of reactive oxygen species, plays critical roles in many physiological and pathological processes. In this work, we designed a simple coumarin-based fluorescent probe, Cou–HOCl, for detecting HOCl in inflammatory cells.