A Near-Infrared Ratiometric Fluorescent Probe for Highly Selective Recognition and Bioimaging of Cysteine

Recent advances in small-molecule fluorescent probes with the function of targeting cancer receptors

Cancer is "the sword of Damocles" that threatens human life and health. Therefore, the diagnosis and treatment of cancer have been receiving much attention. Many overexpressed receptors on the surface of cancer cells provide us with an effective way to specifically identify the cancer cells, and receptor targeting strategies are becoming one of the hot ideas to enhance the ability of fluorescent probes to target tumors. Fluorescent probes connected to ligands are targeted at cancer cell surfaces through receptor-mediated endocytosis. Receptor-targeting probes can image and track cancer cells, determine tumor boundaries, monitor deep lesions, and play a role in clinical medicine, such as fluorescent imaging-guided surgery. In this review, based on the perspective of small molecule fluorescent probes, we reviewed the design ideas, photophysical properties, and applications of receptor-targeting probes for detecting biomarkers in imaging and tracing cancer cells and prospected the future developmental direction of such probes. We hope that this review will provide more ideas for the design and development of active targeting probes for receptors and lead to more applications in the medical field.

Discovery of the cysteine dynamics during the development and treatment of diabetic process by fluorescent imaging

Herein, a novel fluorescent probe RhoDCM was developed for monitoring the cysteine (Cys) dynamics. For the first time, the Cys-triggered implement was applied in relatively complete diabetic mice models. The response of RhoDCM towards Cys suggested advantages including practical sensitivity, high selectivity, rapid reaction, and steadiness in various pH and temperature conditions. RhoDCM could basically monitor the intracellular Cys level, both exogenous and endogenous. It could further monitor the glucose level via detecting consumed Cys. Furthermore, the diabetic mice models including the no diabetic control group, the induced model groups by streptozocin (STZ) or alloxan, and the treatment groups induced by STZ and treated with vildagliptin (Vil), dapagliflozin (DA), or metformin (Metf) were constructed. The models were checked by oral glucose tolerance test and significant liver-related serum indexes. Based on the models, the in vivo imaging and penetrating depth fluorescence imaging both indicated that RhoDCM could characterize the status of the development and treatment in the diabetic process via monitoring the Cys dynamics. Consequently, RhoDCM seemed beneficial for inferring the order of severity in the diabetic process and evaluating the potency of therapeutic schedules, which might be informatic for correlated investigations.

Near-Infrared Probes for Biothiols (Cysteine, Homocysteine, and Glutathione): A Comprehensive Review

Biothiols (cysteine, homocysteine, and glutathione) are an important class of compounds with a free thiol group. These biothiols plays an important role in several metabolic processes in living bodies when present in optimum concentration. Researchers have developed several probes for the detection and quantification of biothiols that can absorb in UV, visible, and near-infrared (NIR) regions of the electromagnetic spectrum. Among them, NIR organic probes have attracted significant attention due to their application in in vivo and in vitro imaging. In this review, we have summarized probes for these biothiols, which could work in the NIR region, and discussed their sensing mechanism and potential applications. Along with focusing on the pros and cons of the reported probes we have classified them according to the fluorophore used and summarized their photophysical and sensing properties (emission, response time, limit of detection).

Lighting Nanoscale Insulators by Steric Restriction-Induced Emissions

Luminescence detection is a sensitive approach for high-resolution visualization of nano-/macrosized objects, but it is challenging to light invisible insulators owing to their inert surfaces. Herein, we discovered a steric restriction-induced emission (SRIE) effect on nanoscale insulators to light them by fluorogenic probes. The SRIE effect enabled us to specifically differentiate a representative nanoscale insulator, boron nitride (BN) nanosheets, from 18 tested nanomaterials with 420-fold increments of photoluminescence intensity and displayed 3 orders of magnitude linearity for quantitative analysis as well as single-particle level detection. Molecular dynamics simulations indicated that the hydrophobic and electron-resistant surfaces of BN nanosheets restricted intramolecular motions of fluorogenic molecules for blockage of the nonradiative path of excited electrons and activation of the radiative electron transition. Moreover, the lighted BN nanosheets could be successfully visualized in complex cellular and tissue biocontexts. Overall, the SRIE effect will inspire more analytical techniques for inert materials.

A Rapid Near-Infrared Fluorescent Probe for Cysteine Based on Isophorone and its Application in B16 Cell Imaging

A novel near-infrared fluorescent probe SWJT-5 based on dicyanoisophorone was synthesized. It achieved the rapid (within 40 s) and discriminative detection of Cys over Hcy and GSH with a large Stokes shift (205 nm). It showed high selectivity and sensitivity for Cys, and had an obvious enhancement of fluorescence emission. The detection limit was 0.43 μM. This probe also had low background interference and little damage to biological samples. Therefore, SWJT-5 had been applied to bioimaging in living cells successfully.

Activity-Based Photosensitizers with Optimized Triplet State Characteristics Toward Cancer Cell Selective and Image Guided Photodynamic Therapy

Activity-based theranostic photosensitizers are highly attractive in photodynamic therapy as they offer enhanced therapeutic outcome on cancer cells with an imaging opportunity at the same time. However, photosensitizers (PS) cores that can be easily converted to activity-based photosensitizers (aPSs) are still quite limited in the literature. In this study, we modified the dicyanomethylene-4H-chromene (DCM) core with a heavy iodine atom to get two different PSs (DCM_O-I, I-DCM_O-Cl) that can be further converted to aPS after simple modifications. The effect of iodine positioning on singlet oxygen generation capacity was also evaluated through computational studies. DCM_O-I showed better performance in solution experiments and further proved to be a promising phototheranostic scaffold via cell culture studies. Later, a cysteine (Cys) activatable PS based on the DCM_O-I core (DCM_O-I-Cys) was developed, which induced selective photocytotoxicity along with a fluorescence turn-on response in Cys rich cancer cells.

Fluorescent Probes and Mass Spectrometry-Based Methods to Quantify Thiols in Biological Systems

Significance: Fluorescent probes and mass spectrometry are the two most popular and complementary methods to quantify thiols in biological systems. In this review, we focus on the widely used and commercially available methods to detect and quantify thiols in living cells and the general approaches applied in mass spectrometry-based thiol quantification. We hope that this review can serve as a general guide for redox biologists who are interested in thiol species. Sulfur, one of the most important elements in living systems, contributes to every aspect of physiology and pathology. Thiols, including cysteine, homocysteine, glutathione, hydrogen sulfide, and hydropersulfides, are the main players in the redox biology system. Therefore, quantifying these thiol species in biological systems is one of the important steps to understand their roles in biology. Recent Advances: Fluorescent probes and mass spectrometry-based methods have been developed to detect and/or quantify thiols in biological systems. Mass spectrometry-based methods have been the gold standard for metabolite quantification in cells. Fluorescent probes can directly detect or quantify thiol species in living cells with spatial and temporal resolutions. Additionally, organelle-specific fluorescent probes have been widely developed. These two methods are complementary to each other. Critical Issues: Reliable quantification of thiol species using fluorescent probes remains challenging. Future Directions: When developing fluorescent probes, we suggest using both the fluorescent probes and mass spectrometry-based thiol quantification methods to cross-check the results. In addition, we call on chemical biologists to move beyond qualitative probes and focus on probes that can provide quantitative results in live cells. These quantitative measurements based on fluorescent probes should be validated with mass spectrometry-based methods. More importantly, chemical biologists should make their probes accessible to the biology end users. Regarding mass spectrometry-based methods, quantification of the derivatized thiol specifies should fit into the general metabolomics workflow. Antioxid. Redox Signal. 36, 354-365.

Recent Developments in Fluorescent Materials for Heavy Metal Ions Analysis From the Perspective of Forensic Chemistry

Forensic chemistry deals with the analysis of various types of physical evidences related to crime, corresponding to the detection of target substances or elements in complex matrices. There is a vital need for highly selective, rapid, and sensitive biosensing technologies in heavy metal ions analysis especially those from living persons, autopsy, food, water, soil, and other identified substances at very preliminary stages. Fluorescent materials-based method for heavy metal ions detection is one of the most important analytical methods, resulting in the ability to measure analytes in complex matrices with unsurpassed selectivity and sensitivity. In this mini review, different fluorescent materials-based analytical methods aiming at several heavy metal ions detection are exclusively reviewed through a comprehensive literature survey. In addition, current challenges to achieve integrated evidence analysis process are briefly discussed to provide an outlook for heavy metal ions detection based on fluorescent analytical methods in the forensic chemistry field.

Nitrosoarene-catalyzed regioselective aromatic C-H sulfinylation with thiols under aerobic conditions

Aromatic amines and (hetero)arenes, such as indoles and pyrroles, are regioselectively sulfinylated under mild aerobic conditions using nitrosoarenes as a redox-catalyst. The nitrosoarene is involved in the electron transfer process with arenes to generate a crucial arene radical cation intermediate for C-H sulfinylation. The present methodology requires no directing group, can be scaled up easily and is applicable for the late-stage functionalization of drug molecules and natural products with high regioselectivity.

A Förster Resonance Energy Transfer Switchable Fluorescent Probe With H2S-Activated Second Near-Infrared Emission for Bioimaging

Real-time and accurate detection of endogenous hydrogen sulfide is of great biomedical significance. Here, a FRET-based fluorescent probe for ratiometric detection of H₂S was designed to comprise an AIE luminophore TPE as an energy donor and a monochlorinated BODIPY dye as an energy acceptor and H₂S-responsive site. Such a designed probe showed H₂S-dependent ratiometric and light-up NIR-II emission, enabling accurate imaging of H₂S-rich cancer cells and identification of H₂S-rich tumors with high resolution.

Two-isophorone fluorophore-based design of a ratiometric fluorescent probe and its application in the sensing of biothiols

A newly designed ratiometric fluorescent probe is applied in the sensing of biothiols.