Ratiometric fluorescent probe with AIE characteristics for hypochlorite detection and biological imaging

It is very important and highly valuable to detect ClO- in samples and living cells with accuracy and speed. In this work, a novel fluorescent probe NA was prepared from 4-bromo-1,8-naphthalic anhydride by acylation reaction and Suzuki coupling reaction and used for the detection of ClO-. Thiomethyl serves as the recognition group for probe NA, while naphthalimide serves as fluorescent chromophore. The probe exhibited an extremely pronounced blue shift from yellow to blue fluorescence within 1 min after the addition of hypochlorite (ClO-). The probe demonstrates high sensitivity to ClO- with a limit of detection (LOD) of 1.22 µM. Also, probe NA demonstrates excellent selectivity and immunity to interference. Additionally, simple fluorescent test strips containing probe NA were prepared in this study, enabling rapid detection of ClO- in water samples. And NA had been effectively used to image endogenous and exogenous ClO-fluorescence in living cells. The results suggest that probe NA has significant potential for portable detection and biological applications.

Dual NIR-channel fluorescent probe for detecting ONOO- in vitro and vivo

As one of endogenous reactive oxygen species (ROS), peroxynitrite (ONOO-) performs various functions in both pathological and physiological mechanisms. In this work, an optical and near-infrared (NIR) fluorescent probe (NX), which based on 3-dihydro-1H-xanthene and 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) group was designed and prepared to detect ONOO-. This probe revealed an obvious optical and a fluorescent response when ONOO- was present and it exhibited higher selectivity over other ROS. Especially, the dual NIR fluorescence changes at 660 and 800 nm allowed quantitative detection of ONOO- in the range of 15-40 μM, and the detection limit was 82 nM. Finally, the probe was effectively employed to visualize exogenous and endogenous ONOO- in HepG2 cells and zebrafish, respectively. All the results indicated the dual NIR-channel probe could serve as a potent detecting tools in studying ONOO- in vitro and in vivo.

A Novel NIR Fluorescent Probe for Rapid Response to Hydrogen Sulfide

Hydrogen sulfide (H2S), as an important small molecule bioregulator, plays a key role in many physiological activities and signaling, and abnormal fluctuations in H2S concentration can lead to a variety of diseases. Therefore, it is of great significance to develop a near-infrared fluorescence probe to visualize fluctuations in H2S levels. This work is based on Sulfur-substituted dicyanomethylene-4 H-chromene (DCM), A novel NIR fluorescent probe (E) -3 - (2 - (4 - (dicyanomethylene) -6-methyl-4 H-Thiochromen-2-yl)vinyl-1-methylquinolin-1-ium (DMT) was synthesized successfully. Research has found that in weakly alkaline environments, the probe DMT reacts rapidly with H2S (only 10 s), the fluorescence intensity at 684 nm is enhanced by about 60 fold, the detection limit is as low as 0.1623 µM, the Stokes shift is large (94 nm), and strong selectivity as well as anti-interference ability towards H2S. This will provide a new method for the rapid detection and further application of H2S.

Super-resolution imaging for in situ monitoring sub-cellular micro-dynamics of small molecule drug

Small molecule drugs play a pivotal role in the arsenal of anticancer pharmacological agents. Nonetheless, their small size poses a challenge when directly visualizing their localization, distribution, mechanism of action (MOA), and target engagement at the subcellular level in real time. We propose a strategy for developing triple-functioning drug beacons that seamlessly integrate therapeutically relevant bioactivity, precise subcellular localization, and direct visualization capabilities within a single molecular entity. As a proof of concept, we have meticulously designed and constructed a boronic acid fluorescence drug beacon using coumarin-hemicyanine (CHB). Our CHB design includes three pivotal features: a boronic acid moiety that binds both adenosine triphosphate (ATP) and adenosine diphosphate (ADP), thus depleting their levels and disrupting the energy supply within mitochondria; a positively charged component that targets the drug beacon to mitochondria; and a sizeable conjugated luminophore that emits fluorescence, facilitating the application of structured illumination microscopy (SIM). Our study indicates the exceptional responsiveness of our proof-of-concept drug beacon to ADP and ATP, its efficacy in inhibiting tumor growth, and its ability to facilitate the tracking of ADP and ATP distribution around the mitochondrial cristae. Furthermore, our investigation reveals that the micro-dynamics of CHB induce mitochondrial dysfunction by causing damage to the mitochondrial cristae and mitochondrial DNA. Altogether, our findings highlight the potential of SIM in conjunction with visual drug design as a potent tool for monitoring the in situ MOA of small molecule anticancer compounds. This approach represents a crucial advancement in addressing a current challenge within the field of small molecule drug discovery and validation.

Mitochondrial-Targeted Ratiometric Near-Infrared Fluorescence Probe for Monitoring Nitric Oxide in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a destructive autoimmune disease, where nitric oxide (NO) is closely implicated in the inflammatory processes of RA. Therefore, direct visualization of NO is essential to assess the pathological changes in RA. Herein, a mitochondrial-targeted near-infrared ratiometric fluorescent probe (NFL-NH2), based on the intramolecular charge transfer effect, was synthesized and applied to monitor the changes of NO content in early RA. Specially, probe NFL-NH2 showed a 44-fold fluorescent intensity ratio (I705/I780) response toward NO with a detection limit of 0.536 nM, enabling qualitative and quantitative analysis of NO. Additionally, NFL-NH2 can accurately target mitochondria and sensitively detect exogenous and endogenous NO in RAW 264.7 cells. Notably, in vivo RA monitoring assays demonstrated that NFL-NH2 can rapidly detect NO levels associated with the inflammatory damage degree in RA mice models by ratiometric fluorescence imaging. These results validate that NFL-NH2 holds significant potential for diagnosing NO-mediated RA diseases.

A multi-signal mitochondria-targeted fluorescent probe for simultaneously distinguishing biothiols and realtime visualizing its metabolism in cancer cells and tumor models

Biothiols and its metabolite SO2 derivatives play vital roles in various physiological processes. Although a few probes have been designed for monitoring the metabolism of biothiols, developing multi-signal fluorescent probes with practicability for simultaneously distinguishing biothiols (GSH, Cys and Hcy) and real-time visualizing SO2 derivatives is an enormous challenge. To better visualize biothiols metabolism in vitro and vivo, we developed a novel multi-signal NIR fluorescent probe (probe 2) with mitochondria-targeted for distinguishing biothiols and its metabolism, based on an ICT-PET synergetic mechanism. Probe 2 with dual recognition sites distinguishing detected Cys/Hcy (Red-Green), GSH (Green) and SO32- (Blue) via three channels. First probe 2 distinguished Cys and GSH to estimate main biothiols in living cells through the ratio changes of two well-defined emission bands (Red-Green), and then imaged its metabolite SO2 with ratiometric fluorescence (Red-Blue), eliminating the interference by different biothiols. Notably, probe 2 exhibits satisfactory sensitivity (detection limit: 0.21, 0.13, 0.14 and 3.06 μM for Cys, Hcy, GSH and SO32-, respectively), high selectivity, reliability at physiological pH, and rapid fluorescence response (within 10 min). Given these advantages, probe 2 has been successfully applied to the real-time monitor GSH metabolic process in MCF-7 cells and biothiols metabolism in breast cancer, suggesting biothiols metabolic changes might be a diagnostic indicator during cancer treatment. So probe 2 is a convenient and efficient tool for understanding the physiological functions of biothiols and its metabolism.

Activatable fluorescent probes for imaging and diagnosis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease that is primarily manifested as synovitis and polyarticular opacity and typically leads to serious joint damage and irreversible disability, thus adversely affecting locomotion ability and life quality. Consequently, good prognosis heavily relies on the early diagnosis and effective therapeutic monitoring of RA. Activatable fluorescent probes play vital roles in the detection and imaging of biomarkers for disease diagnosis and in vivo imaging. Herein, we review the fluorescent probes developed for the detection and imaging of RA biomarkers, namely reactive oxygen/nitrogen species (hypochlorous acid, peroxynitrite, hydroxyl radical, nitroxyl), pH, and cysteine, and address the related challenges and prospects to inspire the design of novel fluorescent probes and the improvement of their performance in RA studies.

Mitochondrial Targeting and Imaging with Small Organic Conjugated Fluorophores: A Review

The last decade has seen an increasingly large number of studies reporting on the development of novel small organic conjugated systems for mitochondrial imaging exploiting optical signal transduction pathways. Mitochondria are known to play a critical role in a number of key biological processes, including cellular metabolism. Importantly, irregularities on their working function are nowadays understood to be intimately linked to a range of clinical conditions, highlighting the importance of targeting mitochondria for therapeutic benefits. In this work we carry out an in-depth evaluation on the progress to date in the field to pave the way for the realization of superior alternatives to those currently existing. The manuscript is structured by commonly used chemical scaffolds and comprehensively covers key aspects factored in design strategies such as synthetic approaches as well as photophysical and biological characterization, to foster collaborative work among organic and physical chemists as well as cell biologists.

A red-emissive benzothiazole-based luminophore with ESIPT and AIE natures and its application for detecting and imaging hypochlorous acid

A new "ESIPT + AIE" based dye of benzothiazole with red emission and a large Stokes shift was constructed by combining 2-(2'-hydroxyphenyl)benzothiazole as the ESIPT unit and α-cyanostilbene as the AIE unit. The compound BACN was found to be a ideal HClO chemosensor, and presented palpable fluorescence and colorimetric responses toward HClO via the HClO-trigged oxidation cleavage of the ethylene bridge activated by the electron withdrawing cyano group. BACN was capable of recognizing HClO rapidly (12 s) and sensitively under physiological conditions, with good selectivity over other biologically pertinent substances. Thanks to strong red emission (λ_em = 606 nm) and large Stokes shift (213 nm) resulted from the combination of ESIPT and AIE effects, it was successfully utilized for the recognition of exogenous and endogenous HClO in living HeLa cells.

Unraveling the Chemosensing Mechanism by the 7-(Diethylamino)coumarin-hemicyanine Hybrid: A Ratiometric Fluorescent Probe for Hydrogen Peroxide

The hemicyanine hybrid containing the 7-(diethylamino)coumarin (ACou) donor attached to the cationic indolenium (Ind) acceptor through a vinyl linkage (ACou-Ind) represents a classic ratiometric fluorescent probe for detecting nucleophilic analytes, such as cyanide and reactive sulfur species (RSS), through addition reactions that disrupt dye conjugation to turn off red internal charge transfer (ICT) fluorescence and turn on blue coumarin emission. The chemosensing mechanism for RSS detection by ACou-Ind suggested in the literature has now been revised. Our studies demonstrate that thiolates react with ACou-Ind through conjugate addition to afford C4-SR adducts that lack coumarin fluorescence due to photoinduced electron transfer quenching by the electron-rich enamine intermediate. Thus, ACou-Ind serves as a turn-off probe through loss of red ICT fluorescence upon RSS addition. The literature also suggests that blue coumarin emission of thiolate adducts is enhanced in the presence of reactive oxygen species (ROS) due to ROS-mediated cellular changes. Our studies predict that such a scenario is unlikely and that thiolate adducts undergo oxidative deconjugation in the presence of H₂O₂, the pervasive ROS. Under basic conditions, H₂O₂ also reacts directly with ACou-Ind to generate intense coumarin fluorescence through an epoxidation process. The relevance of our chemosensing mechanism for ACou-Ind was assessed within live zebrafish, and implications for the utility of ACou-Ind for unraveling the interplay between RSS and ROS are discussed.

A super sensitive fluorescent probe for imaging endogenous hydrogen sulfide in living cells

Hydrogen sulfide (H₂S) that typically performs biphasic biological functions in organisms plays an opposite role at the concentrations above or below normal level of the organism. Therefore, it is significant to develop a fluorescent probe with high sensitivity and selectivity and rapid response for the detection of hydrogen sulfide in vivo. The work describes the design and biological applications of a novel turn-on fluorescence probe SS-N₃ in which the quinoline quaternary ammonium salt derivative is introduced as the fluorescent skeleton and azide is employed as the detection group of H₂S. The probe SS-N₃ shows strong fluorescence at 610 nm, as the azide group is reduced to an amino group by H₂S. The probe SS-N₃ shows high selectivity to H₂S than other anions and some biological mercaptans, and strong anti-interference capacity. In addition, the probe SS-N₃ exhibits little cytotoxicity, improved photostability and large Stokes shift (135 nm), as well as can be effectively used as an indicator of H₂S level in living cells.

A bifunctional fluorescent probe based on PET & ICT for simultaneously recognizing Cys and H2S in living cells

Most reported probes that respond to Cysteine (Cys) and Hydrogen sulfide (H₂S) can only identify one analyte, or they were interfered with homocysteine (Hcy) and glutathione (GSH) when recognizing Cys and H₂S. In addition, nitrobenzoxadiazole (NBD) ether, as one of thiols recognition sites, inevitably encounters the situation that Cys, GSH and H₂S cannot be distinguished on the same channel at the cellular level. In this work, by introducing NBD ether and NBD amine, we constructed a bifunctional fluorescent probe NJB for dual-site response to Cys and H₂S via PET & ICT processes. NJB has wonderful selectivity for identifying Cys and HS^-, with limits of detection as low as 58.4 nM and 81.1 nM, respectively. Interestingly, NJB has been successfully applied to detect Cys and HS^- in MCF-7 cells. Therefore, the probe that serves as a great tool for inquiring the physiological and pathological functions of Cys and H₂S in living cells is promising.

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.

Stress response decay with aging visualized using a dual-channel logic-based fluorescent probe

Diagnosing aging for preventative intervention generally relies on the tracking of aging biomarkers in the resting state. However, the static marker levels are insufficient to fully evaluate aging, particularly given that the stress response capacity (SRC) decay is currently viewed as a critical feature of aging. Therefore, we have developed a dual-channel fluorescent probe ROKS capable of the logic-based visualization of thiophenol (stressor) and HOCl (thiophenol-activated stress response product) in vivo, which provides a new strategy from the time dimension to precisely assess the SRC of individuals under stress using the dual-channel fluorescence ratio. Using ROKS we observed that the SRC of live cells decayed with senescence, and that a higher SRC was found for young vs. aged Caenorhabditis elegans. As such, our study offers a promising strategy for the fluorescence-guided diagnosis of aging and paves the way for accurate evaluation of the efficacy of anti-aging drugs.

Rather than tracking aging using the resting state, ROKS, an optical probe, was developed for evaluating the degree of aging dynamically by precisely monitoring the stress response of individuals under stress.

Rational design of AIE-based fluorescent probes for hypochlorite detection in real water samples and live cell imaging

As one kind of important disinfectant and reactive oxygen species (ROS), hypochlorite (ClO^-), plays vital roles in both water treatment and cell homeostasis. In this work, by decorating a series of groups with different electron donating and withdrawing properties on tetraphenylethene (TPE), four aggregation-induced emission (AIE)-based fluorescent probes containing C˭C double bonds as the potential reaction sites named Probe A, B, C and D were constructed, and their sensing performance for ClO^- was systematically studied. The results showed that the substituents can not only effectively tune the photophysical properties of the probes, but also make a significant impact on their sensing performance for ClO^-. Combined with the theoretical calculation results, it can be inferred that the reactivity of the probes for ClO^- can be greatly enhanced with the increase of electron cloud density on the C˭C double bonds by the introduction of strong electron-donating group (EDG) and electron-withdrawing group (EWG) adjacent to the double bonds. Finally, the best performing Probe D was selected and then successfully applied to ClO^- detection in real water samples and live cell imaging.

Hemicyanine-Based Near-Infrared Activatable Probes for Imaging and Diagnosis of Diseases

Molecular activatable probes with near-infrared (NIR) fluorescence play a critical role in in vivo imaging of biomarkers for drug screening and disease diagnosis. With structural diversity and high fluorescence quantum yields, hemicyanine dyes have emerged as a versatile scaffold for the construction of activatable optical probes. This Review presents a survey of hemicyanine-based NIR activatable probes (HNAPs) for in vivo imaging and early diagnosis of diseases. The molecular design principles of HNAPs towards activatable optical signaling against various biomarkers are discussed with a focus on their broad applications in the detection of diseases including inflammation, acute organ failure, skin diseases, intestinal diseases, and cancer. This progress not only proves the unique value of HNAPs in preclinical research but also highlights their high translational potential in clinical diagnosis.

A lysosome-targetable two-photon excited near-infrared fluorescent probe for visualizing hypochlorous acid-involved arthritis and its treatment

Lysosome of phagocyte is the main site of hypochlorous acid (HClO) production, and HClO can be employed as the biomarker for the diagnosis and treatment evaluation of arthritis. In recent years, developing fluorescent probes for lysosomal HClO has attracted considerable attention, but most of them still have some defects, such as autofluorescence, phototoxicity and photobleaching because of their excitation and emission located in short-wavelength region. Due to the advantages of two-photon fluorescent probes with near-infrared emissions, a lysosome-targetable two-photon fluorescent probe (Lyso-TP-HClO) with a near-infrared emission was reported in this paper. Lyso-TP-HClO has a high selectivity and a high sensitivity to HClO in the linear range (10.0 × 10^-8 to 5.0 × 10^-6 M), with a detection limit of 3.0 × 10^-8 M. Due to the two-photon excited near-infrared emission, Lyso-TP-HClO has excellent imaging performances, such as small autofluorescence, excellent photostability, and large imaging depth. Furthermore, Lyso-TP-HClO was successfully employed for visualizing lysosomal HClO in bacteria-infected cells. At last, we have successfully used Lyso-TP-HClO to image the arthritis and evaluate the treatment of arthritis in mice. All the results confirm that Lyso-TP-HClO is a useful chemical tool for imaging of lysosomal HClO, the diagnosis of arthritis, and treatment evaluation of arthritis.

Recent development of synthetic probes for detection of hypochlorous acid/hypochlorite

Hypochlorous acid/hypochlorite (HOCl/OCl^-), as one of the most important reactive oxygen species (ROS), plays an important role in various physiological and pathological processes. Nonproperly located or abnormal concentration of OCl^-, however, is associated with many diseases. Thus, developing the fluorescent probe for detecting OCl^- is of great significance. To this end, in last decade, many fluorescent probes have been developed and applied for detecting HOCl/OCl^- in vitro and in vivo. Despite a great progress has achieved, the development and application of near-infrared fluorescent HOCl/OCl^- probe still have some challenges. For example, highly specific and sensitive NIR fluorescent HOCl/OCl^- probes applied in endogenous OCl^- detection and subcellular organelle bioimaging. In this review, we summarized the representative cases of HOCl/OCl^- probes with properties that mentioned above. The discussion contains design strategies, detection mechanisms, as well as applications in bioimaging.

A ratiometric fluorescent probe for imaging enzyme dependent hydrogen sulfide variation in the mitochondria and in living mice

Developing a ratiometric H₂S fluorescent probe with fast response is of great importance for studying the H₂S physiology. Herein, two hemicyanine-based H₂S probes were constructed; the one with a propanoic acid group (CouPa) showed poor sensitivity while the other one with the N,N-diethylpropionamide moiety (CouDE) exhibited distinctly improved performance. CouDE showed the ability to detect mitochondrial H₂S level fluctuation, which was triggered by alteration of CBS enzyme activity. Moreover, endogenous H₂S change in solid tumours was monitored using CouDE.

Additive- and column-free synthesis of rigid bis-coumarins as fluorescent dyes for G-quadruplex sensing via disaggregation-induced emission

A novel and efficient method to synthesize rigid bis-coumarins based on the dimerization of coumarinyl aldehydes was developed. This procedure is additive- and column-free, providing a facile and environment-friendly way to prepare fluorophores. The prepared novel fluorescent bis-coumarins exhibit favorable photophysical properties with good sensitivity and selectivity towards G-quadruplexes (G4s).

The application of nitrogen heterocycles in mitochondrial-targeting fluorescent markers with neutral skeletons

Neutral fluorescent markers containing nitrogen heterocycles as targeting groups were designed and prepared to screen out structural units for targeting mitochondria.