A pyridine-Si-rhodamine-based near-infrared fluorescent probe for visualizing reactive oxygen species in living cells

Visualizing ClO- fluctuations in drug-induced liver injury and bacterium via a robust ratiometric fluorescent probe

As a type of reactive oxygen species, hypochlorous acid (ClO-) plays an important role in sterilization, disinfection and protection in organisms. However, excessive production of ClO- is closely related to various diseases. In this work, we have designed a robust ratiometric fluorescent probe, RDB-ClO, using the excited-state intramolecular proton transfer (ESIPT) strategy. RDB-ClO was achieved by modifying 2-(2-(benzo[d]thiazol-2-yl)-6-(diethylamino)-3-oxo-3H-xanthen-9-yl) benzoic acid (RDB-OH) with a 1-naphthoyl chloride group, specifically for the sensitive detection of ClO-. In the presence of ClO-, RDB-ClO demonstrated relatively good performance, showing swift response time (35 s), low detection limit of 5.1 nM and high selectivity towards ClO-. Notably, the convenience and accessibility detection of ClO- has been implemented using test strip and agarose probe. RDB-ClO effectively tracked both endogenous and exogenous ClO- in HeLa cells, HepG2 cells and zebrafish. Additionally, it is successfully applied to detect changes of exogenous ClO- content in E. coli. and acetaminophen (APAP)-induced liver injury in mice. The development of RDB-ClO represents a promising molecular tool for studying the pathogenesis of DILI and biotransformation of ClO- in bacteria.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Recent progress and outlooks in rhodamine-based fluorescent probes for detection and imaging of reactive oxygen, nitrogen, and sulfur species

Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) serve as vital mediators essential for preserving intracellular redox homeostasis within the human body, thereby possessing significant implications across physiological and pathological domains. Nevertheless, deviations from normal levels of ROS, RNS, and RSS disturb redox homeostasis, leading to detrimental consequences that compromise bodily integrity. This disruption is closely linked to the onset of various human diseases, thereby posing a substantial threat to human health and survival. Small-molecule fluorescent probes exhibit considerable potential as analytical instruments for the monitoring of ROS, RNS, and RSS due to their exceptional sensitivity and selectivity, operational simplicity, non-invasiveness, localization capabilities, and ability to facilitate in situ optical signal generation for real-time dynamic analyte monitoring. Due to their distinctive transition from their spirocyclic form (non-fluorescent) to their ring-opened form (fluorescent), along with their exceptional light stability, broad wavelength range, high fluorescence quantum yield, and high extinction coefficient, rhodamine fluorophores have been extensively employed in the development of fluorescent probes. This review primarily concentrates on the investigation of fluorescent probes utilizing rhodamine dyes for ROS, RNS, and RSS detection from the perspective of different response groups since 2016. The scope of this review encompasses the design of probe structures, elucidation of response mechanisms, and exploration of biological applications.

Recent progress of near-infrared fluorescent probes in the determination of reactive oxygen species for disease diagnosis

Reactive oxygen species (ROS), a chemically defined group of reactive molecules derived from molecular oxygen, are involved in a variety of physiological and pathological processes, including immune defense, cellular metabolism, and other physiological processes. To access their detailed function in these processes, it is critical to establish rapid, accurate and in situ assays for these species in vivo. Among the potential assays, fluorescent probes are considered as the most promising candidate to monitor the biological ROS in vivo with great spatial and temporal resolution and are extensively used as an excellent tool in modern redox biology discovery. Recently, abundant fluorescent probes have been successively developed for in vitro or intracellular detection of ROS, but most of them could not be used for in vivo imaging due to their intrinsic shortcomings such as short emission wavelengths, phototoxicity and poor tissue penetration. Recent development of fluorescent ROS probes with near-infrared emission aim to address these concerns to develop practical assays. Herein, we review recent developments of ROS-sensitive near-infrared fluorescent probes, with an emphasis on the design, synthesis, characteristics of fluorescent probes, as well as their applications. We hope this review will aid the development of a new generation of efficient, sensitive and biocompatible fluorescent probes for in vivo ROS detection.

A Study of Small Molecule-Based Rhodamine-Derived Chemosensors and their Implications in Environmental and Biological Systems from 2012 to 2021: Latest Advancement and Future Prospects

Rhodamine-based chemosensors have sparked considerable interest in recent years due to their remarkable photophysical properties, which include high absorption coefficients, exceptional quantum yields, improved photostability, and significant red shifts. This article presents an overview of the diverse fluorometric, and colorimetric sensors produced from rhodamine, as well as their applications in a wide range of fields. The ability of rhodamine-based chemosensors to detect a wide range of metal ions, including Hg+2, Al3+, Cr3+, Cu2+, Fe3+, Fe2+, Cd2+, Sn4+, Zn2+, and Pb2+, is one of their major advantages. Other applications of these sensors include dual analytes, multianalytes, and relay recognition of dual analytes. Rhodamine-based probes can also detect noble metal ions such as Au3+, Ag+, and Pt2+. They have been used to detect pH, biological species, reactive oxygen and nitrogen species, anions, and nerve agents in addition to metal ions. The probes have been engineered to undergo colorimetric or fluorometric changes upon binding to specific analytes, rendering them highly selective and sensitive by ring-opening via different mechanisms such as Photoinduced Electron Transfer (PET), Chelation Enhanced Fluorescence (CHEF), Intramolecular Charge Transfer (ICT), and Fluorescence Resonance Energy Transfer (FRET). For improved sensing performance, light-harvesting dendritic systems based on rhodamine conjugates has also been explored for enhanced sensing performance. These dendritic arrangements permit the incorporation of numerous rhodamine units, resulting in an improvement in signal amplification and sensitivity. The probes have been utilised extensively for imaging biological samples, including imaging of living cells, and for environmental research. Moreover, they have been combined into logic gates for the construction of molecular computing systems. The usage of rhodamine-based chemosensors has created significant potential in a range of disciplines, including biological and environmental sensing as well as logic gate applications. This study focuses on the work published between 2012 and 2021 and emphasises the enormous research and development potential of these probes.

Valkyrie Probes: A Novel Class of Enzyme-Activatable Photosensitizers based on Sulfur- and Seleno-Rosamines with Pyridinium Unit

The rational design of activatable photosensitizers (aPSs) uncaged by specific disease biomarkers is currently booming due to their positive attributes to achieve targeted photodynamic therapy (PDT). In this context, we present here the synthesis and detailed photophysical characterization of a novel class of hetero-rosamine dyes bearing sulfur or selenium as bridging heavy atom and 4-pyridyl meso-substituent as optically tunable group. The main feature of such photoactive platforms is the spectacular change of their spectral properties depending on the caging/decaging status of their 4-pyridyl moiety (cationic pyridinium vs. neutral pyridine). The preparation of two alkaline phosphatase (ALP)-responsive probes (named Valkyrie probes) was achieved through formal N-quaternarization with 4-phosphoryloxybenzyl, the traditional recognition moiety for this important diagnostic enzyme. Bio-analytical validations including fluorescence/singlet oxygen phosphorescence enzyme assays and RP-HPLC-fluorescence/-MS analyses have enabled us to demonstrate the viability and effectiveness of this novel photosensitizer activation strategy. Since sulfur-containing Valkyrie probe also retains high fluorogenicity in the orange-red spectral range, this study highlights meso-pyridyl-substituted S-pyronin scaffolds as valuable candidates for the rapid construction of molecular phototheranostic platforms suitable for combined fluorescence diagnosis and PDT.

Depletion of reactive oxygen species induced by beetroot (Beta vulgaris) extract leads to apoptosis-like death in Cronobacter sakazakii

This research aimed to disclose the antibacterial activity of beetroot extract (Beta vulgaris) against Cronobacter sakazakii and its possible mechanisms. We evaluated its antibacterial activity by measuring the minimum inhibitory concentration (MIC) and time-kill kinetics. We also evaluated the intracellular ATP levels, bacterial apoptosis-like death (ALD), and reactive oxygen species (ROS) levels to reveal the possible antibacterial mechanisms. Our results showed that the MIC of beetroot extract against C. sakazakii was 25 mg/mL and C. sakazakii (approximately 8 log cfu/mL) was completely inhibited after treatment with 2 MIC of beetroot extract for 3 h. Beetroot extract reduced intracellular ATP levels and facilitated characteristics of ALD in C. sakazakii, such as membrane depolarization, increased intracellular Ca²⁺ levels, phosphatidylserine externalization, caspase-like protein activation, and DNA fragmentation. Additionally, and different from most bacterial ALD caused by the accumulation of ROS, beetroot extract reduced the intracellular ROS levels in C. sakazakii. Our experimental data provide a rationale for further research of bacterial ALD and demonstrate that beetroot extract can inhibit C. sakazakii in food processing environments.

New insight into the application of fluorescence platforms in tumor diagnosis: From chemical basis to clinical application

Early and rapid diagnosis of tumors is essential for clinical treatment or management. In contrast to conventional means, bioimaging has the potential to accurately locate and diagnose tumors at an early stage. Fluorescent probe has been developed as an ideal tool to visualize tumor sites and to detect biological molecules which provides a requirement for noninvasive, real-time, precise, and specific visualization of structures and complex biochemical processes in vivo. Rencently, the development of synthetic organic chemistry and new materials have facilitated the development of near-infrared small molecular sensing platforms and nanoimaging platforms. This provides a competitive tool for various fields of bioimaging such as biological structure and function imaging, disease diagnosis, in situ at the in vivo level, and real-time dynamic imaging. This review systematically focused on the recent progress of small molecular near-infrared fluorescent probes and nano-fluorescent probes as new biomedical imaging tools in the past 3-5 years, and it covers the application of tumor biomarker sensing, tumor microenvironment imaging, and tumor vascular imaging, intraoperative guidance and as an integrated platform for diagnosis, aiming to provide guidance for researchers to design and develop future biomedical diagnostic tools.

Rhodol-Based Fluorescent Probes Used for Fast Response toward ClO– and Delayed Determination of H2O2 in Living Cells

Reactive oxygen species (ROS), a class of reactive oxidants, play critical roles in signal transduction, cell metabolism, immune defense, and other physiological processes. Abnormally excessive levels of ROS can cause diseases and thus, investigations into the relevant biology and medicine are significant. The behavior of ROS in inflammation has been rarely elucidated. In this work, two ROS fluorescent probes, FS-ROS1 and FS-ROS2 have been designed and synthesized. FS-ROS1 responds rapidly (~1 min) to ClO– and gradually (~30 min) to H2O2 with an increase in fluorescence at ~656 nm and 640 nm of more than 100-fold in vitro. At a concentration of 10 μM, FS-ROS1 labels the L929 cell and Raw264.7 cell wells in 30 min with excellent biocompatibility and without washing. After labelling, FS-ROS1 exhibited a rational fluorescence increase upon the addition of 1, 10, 100, and 200 μM of H2O2. Based on these results, inflammatory cells, stimulated with 800 nM dexamethasone and polyIC, showed a higher increase in fluorescence than the control cells. These results suggest that H2O2 and ClO– might be important signaling molecules during inflammations.

Carbon dot based nucleus targeted fluorescence imaging and detection of nuclear hydrogen peroxide in living cells

Investigation of the intracellular generation of H₂O₂, one of the most important reactive oxygen species (ROS), is crucial for preventing various diseases since it is closely linked with different physiological and complex cell signaling pathways. Despite the development of various fluorescent probes, the majority of the fluorescent probes cannot move across the nuclear membrane. However, detection of the nuclear level of H₂O₂ is very important since it can directly cause oxidative DNA damage which ultimately leads to various diseases. Therefore, in this study, p-phenylenediamine based carbon quantum dots (B-PPD CDs) have been synthesized and integrated with 4-formylbenzeneboronic acid as a doping agent for the detection of H₂O₂. The detection mechanism showed that, upon exposure to H₂O₂, the fluorescence of the B-PPD CDs was immediately quenched. Further investigation has been done in the in vitro RAW 264.7 cell line by both exogenous and endogenous exposure of H₂O₂ to demonstrate the feasibility of the method. It is shown successfully that the exogenous presence and endogenous generation of H₂O₂ in RAW 264.7 cells can be detected using B-PPD CDs. The limit of detection (LOD) was determined to be 0.242 μM. The development of such imaging probes using carbon quantum dots will lead to live-cell imaging as well as ROS detection.