A near-infrared fluorescent probe for tracking endogenous and exogenous H2O2 in cells and zebrafish

H2O2 is an important signaling molecule in the body, and its levels fluctuate in many pathological sites, therefore, it can be used as a biomarker for early diagnosis of disease. Since the environment in vivo is extremely complex, it is of great significance to develop a probe that can accurately monitor the fluctuation of H2O2 level without interference from other physiological processes. Based on this, we designed and synthesized two new near-infrared H2O2 fluorescent probes, LTA and LTQ, based on the ICT mechanism. Both of them have good responses to H2O2, but LTA has a faster response speed. In addition, the probe LTA has good biocompatibility, good water solubility, and a large Stokes shift (95 nm). The detection limit is 4.525 μM. The probe was successfully used to visually detect H2O2 in living cells and zebrafish and was successfully used to monitor the changes in H2O2 levels in zebrafish due to APAP-induced liver injury.

Activity-Based Sensing for Chemistry-Enabled Biology: Illuminating Principles, Probes, and Prospects for Boronate Reagents for Studying Hydrogen Peroxide

Activity-based sensing (ABS) offers a general approach that exploits chemical reactivity as a method for selective detection and manipulation of biological analytes. Here, we illustrate the value of this chemical platform to enable new biological discovery through a case study in the design and application of ABS reagents for studying hydrogen peroxide (H2O2), a major type of reactive oxygen species (ROS) that regulates a diverse array of vital cellular signaling processes to sustain life. Specifically, we summarize advances in the use of activity-based boronate probes for the detection of H2O2 featuring high molecular selectivity over other ROS, with an emphasis on tailoring designs in chemical structure to promote new biological principles of redox signaling.

Tracking Autophagy Process with a TBET and AIE-Based Ratiometric Two-Photon Viscosity Probe

Autophagy is a cellular self-degrading process that plays a key role in cellular health and functioning. Since autophagy disorder is related to many diseases, it is highly important to detect autophagy. This study aimed to establish a dual-sensing mechanism-based ratiometric viscosity-sensitive lysosome-targeted two-photon fluorescent probe Vis-sun to track the autophagy process (the increase in lysosome viscosity during autophagy) by combining through bond energy transfer (TBET) and aggregation-induced emission (AIE). The introduction of TBET not only overcame the interference of background signals but also achieved the baseline separation of two emission peaks, thus reducing the crosstalk between emissions, as well as the noninvasive bio-sensing of biological targets and long-term real-time tracer imaging by introducing AIE. In vitro experiments showed that the fluorescence intensity at 485 nm decreased gradually on increasing the volume ratio of water to tetrahydrofuran (V_water/V_THF), while the fluorescence intensity at 605 nm increased significantly. Also, the fluorescence signal was maximized when the water content reached 100%. At the same time, the probe exhibited a significant dependence on the ambient viscosity. Therefore, the dynamic monitoring of lysosome viscosity during autophagy and the in situ imaging of autophagy fluctuations during stroke-induced neuroinflammation were successfully achieved by implementing Vis-sun lysosome anchoring with morpholine.

Fluorescent probes for biomolecule detection under environmental stress

The use of fluorescent probes in visible detection has been developed over the last several decades. Biomolecules are essential in the biological processes of organisms, and their distribution and concentration are largely influenced by environmental factors. Significant advances have occurred in the applications of fluorescent probes for the detection of the dynamic localization and quantity of biomolecules during various environmental stress-induced physiological and pathological processes. Herein, we summarize representative examples of small molecule-based fluorescent probes that provide bimolecular information when the organism is under environmental stress. The discussion includes strategies for the design of smart small-molecule fluorescent probes, in addition to their applications in biomolecule imaging under environmental stresses, such as hypoxia, ischemia-reperfusion, hyperthermia/hypothermia, organic/inorganic chemical exposure, oxidative/reductive stress, high glucose stimulation, and drug treatment-induced toxicity. We believe that comprehensive insight into the beneficial applications of fluorescent probes in biomolecule detection under environmental stress should enable the further development and effective application of fluorescent probes in the biochemical and biomedical fields.

Application of Fluorescent Probes in Reactive Oxygen Species Disease Model

Reactive oxygen species (ROS) play an important role in living activities as signaling molecules that regulate the living activities of organisms. There are many types of ROS, mainly including hydrogen peroxide (H2O2), hypochlorous acid (HOCl), hydroxyl radical (•OH), peroxyl radical (ROO•), singlet oxygen (1O2), peroxynitrite (ONOO-) and superoxide anion radical (O2-•) etc. Existing studies have shown that changes in ROS levels are closely associated with the development of many diseases, such as inflammation, cancer, cardiovascular disease, and neurodegenerative damage. Small molecule fluorescent probes have been widely used in biology, pathology and medical diagnosis due to their advantages of noninvasive, high sensitivity and in vivo real-time detection. It is extremely important to better apply small-molecule fluorescent probes to detect ROS levels in organisms to achieve early diagnosis of diseases and assessment of therapeutic conditions. This work focuses on summarizing the representative applications of some fluorescent probes in ROS disease models in recent years. This article focuses on summarizing the construction methods of various ROS-related disease models, and classifying and analyzing the basic ideas and methods of fluorescent probes applied to disease models according to the characteristics of various diseases.

Near-Infrared in and out: Observation of Autophagy during Stroke via a Lysosome-Targeting Two-Photon Viscosity-Dependent Probe

Fluorescence imaging using probes with two-photon excitation and near-infrared emission is currently the most popular in situ method for monitoring biological species or events, with a large imaging depth, low background fluorescence, low optical damage, and high spatial and temporal resolution. Nevertheless, current fluorescent dyes with near-infrared emission still have some disadvantages such as poor water solubility, low fluorescence quantum yield, and small two-photon absorption cross sections. These drawbacks are mainly caused by the structural characteristics of dyes with large conjugation surfaces but lacking strong and rigid structures. Herein, a lysosome-targeted and viscosity-sensitive probe (NCIC-VIS) is designed and synthesized. The protonation of morpholine not only helps anchor NCIC-VIS to the lysosome but also significantly enhances its water solubility. More importantly, its viscosity can increase the rigid structure of NCIC-VIS, which will improve the fluorescence quantum yield and the two-photon absorption cross section due to the imposed restrictions on molecular torsion. Based on the abovementioned characteristics, the real-time imaging of cellular autophagy (could increase the viscosity of lysosomes) was realized using NCIC-VIS. The results demonstrated that the level of autophagy was significantly enhanced in mice during stroke, while the inhibition of oxidative stress significantly reduced the degree of autophagy. The study corroborates that oxidative stress induced by stroke can lead to the development of autophagy.

Observation of macrophage autophagy in the healing of diabetic ulcers via a lysosome-targeting polarity-specific two-photon probe

As a disease with high incidence, mutilation, and fatality rates, diabetic ulcers (DUs) have become a difficult and complicated disease of widely concern in recent years due to the unclear healing mechanism. The main reason for the delayed healing in DU patients is the unduly long chronic inflammation window, and the polarization state of macrophages plays a key role in this process. Since autophagy is believed to be closely related to the polarization trend of macrophages, recent studies have shown that autophagy is closely related to the healing of DU. To this end, a lysosome-targeting polarity-sensitive probe, XZTU-VIS, was developed to monitor the changes in lysosomal polarity, thereby assessing the autophagy of macrophages in mice suffering from DU. The experimental results showed that under two-photon fluorescence microscopy, the green channel fluorescence signal of XZTU-VIS decreased significantly during autophagy. In the meantime, DU models established using BV-2 cells and mice showed a process that could cause inflammation and the release of ROS, thereby inducing autophagy.

A polarity-dependent two-photon fluorescent probe for evaluation of autophagy in the process of diabetic mouse skin ulcer-induced inflammation was constructed.

Recent Advances in Hydrogen Peroxide Responsive Organoborons for Biological and Biomedical Applications

Hydrogen peroxide is the most stable reactive oxygen species generated endogenously, participating in numerous physiological processes and abnormal pathological conditions. Mounting evidence suggests that a higher level of H₂ O₂ exists in various disease conditions. Thus, H₂ O₂ functions as an ideal target for site-specific bioimaging and therapeutic targeting. The unique reactivity of organoborons with H₂ O₂ provides a method for developing chemoselective molecules for biological and biomedical applications. This review highlights the design and application of boron-derived molecules for H₂ O₂ detection, and the utility of boron moieties toward masking reactive compounds leading to the development of metal prochelators and prodrugs for selectively delivering an active species at the target sites with elevated H₂ O₂ levels. Additionally, the emergence of H₂ O₂ -responsive theranostic agents consisting of both therapeutic and diagnostic moieties in one integrated system are discussed. The purpose of this review is to provide a better understanding of the role of boron-derived molecules toward biological and pharmacological applications.

A biotin-guided two-photon fluorescent probe for detection of hydrogen peroxide in cancer cells ferroptosis process

Hydrogen peroxide (H₂O₂) plays a vital role in organism due to its strong oxidizability, especially in resisting the invasion of pathogens. Cancer cells have abnormal concentrations of hydrogen peroxide due to their disordered reproduction. In complex biological systems, however, conventional fluorescent probes based solely on their fluorescent response to abnormal H₂O₂ overexpression in cancer cells are not enough to distinguish cancer cells from other unhealthy or immune cells. Therefore, it is necessary to develop other methods to allow the probe to selectively enter the cancer cells and perform fluorescence imaging of the hydrogen peroxide in the cancer cells. Herein, we developed a biotin-guided, two-photon fluorescent probe (BT-HP) for sensitive detection of H₂O₂ in cancer cells. Through the study on the properties of the probe, it was found that the probe can selectively enter cancer cells. The depth penetration imaging of H₂O₂ in cancer cells and tumor tissues by two-photon microscope proves the potential of the probe BT-HP as a tumor targeting H₂O₂ biosensor. The probe was further applied to detect hydrogen peroxide in cancer cells during the ferroptosis process.