A novel target and pH dual-activatable fluorescent probe for precisely detecting hypochlorite in lysosomes

A specific dual-locked fluorescence probe to visualize the dynamic changes of lipid droplets and hypochlorous acid in inflammation

Inflammation is a key factor leading to the occurrence and development of many diseases, both lipid droplets (LDs) and hypochlorous acid (HClO/ClO-) are regarded as the important biomarkers of inflammation. Therefore, it is of great significance to develop an efficient single chemical sensor that can simultaneously detect these two biomarkers. To achieve the goal, we developed a dual-locked fluorescence probe (TPA-DNP) by fusing two targets activated reporting system, its implementation was achieved by turning-on the fluorescence of TPA-DNP through LDs and HClO/ClO- simultaneously. In simulated LDs environment, TPA-DNP displayed excellent selectivity to HClO/ClO-, high sensitivity (LOD = 0.527 μM) and strong anti-interference ability. In addition, cell and zebrafish imaging experiments showed that TPA-DNP could be utilized to visualize exogenous/endogenous HClO/ClO- in LDs environment, and could also be used to observe the impact of LDs changes on the HClO/ClO- detection. On the basis, TPA-DNP served as a favorable tool to achieve visualization of inflammatory dynamic changes.

De Novo Design of a Highly Stable Ratiometric Probe for Long-Term Continuous Imaging of Endogenous HClO Burst

Long-term continuous imaging of endogenous HClO burst is of great importance for the elucidation of various physiological or pathological processes. However, most of the currently reported HClO probes have failed to achieve this goal due to their insufficient photobleaching resistance under a laser source. Herein, a highly stable ratiometric probe, HFTC-HClO 1, which is capable of continuously monitoring endogenous HClO burst over a long period of time, has been judiciously developed. Briefly, the de novo development of HFTC-HClO 1 mainly involved three main steps: (1) novel coumarins (HFTC 1-5) were designed and synthesized; (2) the most stable scaffold, HFTC 3, was selected through dye screening and cell imaging validation; and (3) based on HFTC 3, three candidate HClO probes were constructed, and HFTC-HClO 1 was finally selected due to its superior sensing properties toward HClO. Furthermore, HFTC-HClO 1 can quantitatively measure HClO levels in various real samples with excellent recovery (>90.4%), and the use of HFTC-HClO 1-coated test strips for qualitative analysis of HClO in real samples was also achieved. In addition, the application of HFTC-HClO 1 for long-term continuous monitoring of intracellular HClO burst was successfully demonstrated. Significantly, HFTC-HClO 1 was able to visualize HClO generated in the rheumatoid arthritis mouse model.

A dual-responsive fluorescent probe based on cyanine and naphthalimide units for detecting HClO and H2S in living cells

Hypochlorous acid (HClO) and hydrogen sulfide (H2S) play very important roles in both physiological and pathological processes, however, the methods for simultaneously detecting HClO and H2S were rarely reported. Here, a dual-responsive fluorescent probe (CyNa-N3) based on cyanine and naphthalimide dyes was synthesized and investigated. The fluorescence probe showed better sensitivity, high selectivity response to HClO and H2S by red emission and green emission bands, and the limits of detection were 0.17 µM and 0.15 µM respectively. MS (Mass Spectrum) and 1H NMR (Nuclear Magnetic Resonance) confirmed the sensing mechanism of CyNa-N3 detected HClO and H2S, the calculation of density functional theory (DFT) further explained the internal mechanism of spectral change of CyNa-N3. Moreover, CyNa-N3 was successfully applied to image HClO and H2S in living cells, which is beneficial for more efficient application in biological imaging.

Screening of aggregation-induced emission and multi-response acrylonitrile-bridging fluorescent molecules tailored for rapid turn-on detection of HClO as well as ratiometric visualizing of extreme basicity

Realizing the rapid and sensitive tracing of multiple analysis indicators using single molecular probe through structural designing is urgently desired for exploring novel multi-response chemosensors. Herein, a series of acrylonitrile-bridging organic small molecules have been rationally designed. Among these donor-π-acceptor (D-π-A) compounds with efficient aggregation-induced emission (AIE) characteristics, a unique derivative, 2-(1H-benzo[d]imidazole-2-yl)-3-(4-(methylthio)phenyl) acrylonitrile, named MZS, has been screened out for multifunctional utilizing. First, probe MZS can respond to hypochlorous acid (HClO) through specific oxidation reaction, showing a marked fluorescence turn-on signal (I₄₉₅). This special sensing reaction is ultra-fast with a rather low detection limit (LOD = 13.6 nM). Next, versatile MZS is also sensitive to the extreme pH fluctuation, displaying an intriguing ratiometric signal variation (I₅₄₀/I₄₅₀), facilitating the real-time and naked-eye visualizing, which is even stable and reversible. Furthermore, probe MZS has been used for the monitoring of HClO in real water and commercially available disinfectant spray samples with satisfactory results. We envision that probe MZS would be a flexible and powerful tool for monitoring of environmental toxicity and industrial operations under realistic scenarios.

A naphthalimide-based and Golgi-targetable fluorescence probe for quantifying hypochlorous acid

The Golgi apparatus (GA) is a vital organelle in biological systems and excess reactive oxygen species (ROS) is produced during stress in the Golgi apparatus. Hypochlorous acid (HOCl) is a significant reactive oxygen species and has strong oxidative and antibacterial activity, but excessive secretion of hypochlorous acid can affect Golgi structure or function abnormally, it will lead to a series of diseases including Alzheimer's disease, neurodegenerative diseases, autoimmune diseases, and Parkinson's disease. In present work, a novel fluorescent probe for Golgi localization utilizing naphthalimide derivatives was constructed to detect hypochlorous acid. The fluorescent probe used a derivatived 1,8-naphthalimide as the emitting fluorescence group, phenylsulfonamide as the localization group and dimethylthiocarbamate as the sensing unit. When HOCl was absent, the intramolecular charge transfer (ICT) process of the developed probe was hindered and the probe exhibited a weak fluorescence. When HOCl was present, the ICT process occurred and the probe showed strong green fluorescence. When the HOCl concentration was altered from 5.0 × 10^-7 to 1.0 × 10^-5 mol·L^-1, the fluorescence intensity of the probe well linearly correlated with the HOCl concentration. The detection limit of 5.7 × 10^-8 mol·L^-1 was obtained for HOCl. The HOCl fluorescent probe possessed a rapid reaction time, a high selectivity and a broad working pH scope. In addition, the probe possessed good biocompatibility and had been magnificently employed to image Golgi HOCl in Hela cells. These characteristics of the probe demonstrated its ability to be used for sensing endogenous and exogenous hypochlorous acids within the Golgi apparatus of living cells.

A dicyanoisophorone-based fluorescent probe for hypochlorite with a fast response and its applications in bioimaging

One kind of phenolic substituted dicyanoisophorone derivative (Is-OL) has been designed and successfully synthesized for the detection of hypochlorite in water samples, test strips and living HeLa cells. The probe Is-OL showed high sensitivity and selectivity to hypochlorite over other competitive ROS and metal ions. Moreover, Is-OL can react instantaneously with hypochlorite (<5 s) while exhibiting a significant color change from yellow to colorless, which makes "naked-eye" detection possible with a low detection limit (0.095 μM). The results based on water tests and living HeLa cell experiments showed that Is-OL could be applied as a potential candidate for the detection of hypochlorite.

A deep-red lysosome-targetable fluorescent probe for detection of hypochlorous acid in pure water and its imaging application in living cells and zebrafish

Hypochlorite plays a significant role in physiological processes, particularly regulation of lysosomal functions, and is involved in various diseases. Thus, it is crucial to develop highly sensitive and selective molecule tools to detect HClO in lysosomes. Herein, a novel 2H-benzo[h]chromene-pyridine derivative (1) was synthesized through condensation reaction, which exhibited a notable deep-red emission at 640 nm in pure water. This deep-red emission was specifically quenched by adding ClO^-. The response of probe 1 toward ClO^- was rapid (within 10 s), sensitive (detection limit of 0.012 μM), and effective over a wide range of pH (1.0-12.0). Due to the existence of morpholine as the lysosome-targeting unit, the probe was successfully utilized to monitor lysosomal ClO^-. Moreover, the probe 1 was also applied to detecting ClO^- in zebrafish.

Two-photon ratiometric fluorescent probe for imaging of hypochlorous acid in acute lung injury and its remediation effect

Acute lung injury (ALI) is a pulmonary inflammatory disease with high morbidity and mortality rates. However, owing to the unknown etiology and rapid progression of the disease, the diagnosis of ALI is full of challenges with no effective treatment. Since the inflammatory response and oxidative stress played vital roles in the development of ALI, we herein developed the largest emission cross-shift (△λ = 145 nm) two-photon ratiometric fluorescent probe of TPRS-HOCl with high selectivity and short response time toward hypochlorous acid (HOCl) for exploring the relevance between the degree of ALI and HOCl concentration in the development process of the disease. In addition, the inhibition effect of HOCl during different treatment periods was also evaluated. Moreover, the tendency of imaging results was basically in accordance with that of hematoxylin and eosin (H&E) staining and the treatment effect became better in the early stage when using N-acetylcysteine (NAC), demonstrating the sensitivity of TPRS-HOCl toward ALI response. Thus, TPRS-HOCl has great potential to diagnose ALI in the early stage and guide for effective treatment.

A long-wavelength fluorescent probe with a large Stokes shift for lysosome-targeted imaging of Cys and GSH

Biothiols including cysteine (Cys) and glutathione (GSH) are biological signaling molecules responsible for cell detoxification, cell metabolism and neutralization of reactive oxygen species. Here, we synthesized a long-wavelength fluorescent probe, DCIMA, for lysosome-targeted imaging of Cys and GSH in living cells. DCIMA is consisted of a dicyanoisophorone core modified with an acrylate group for biothiol detection through the Michael addition reaction and a morpholine group as the lysosome-targeting agent. The presence of the electron-donating morpholine group also enhances the intramolecular charge transfer mechanism of the probe, thereby enabling its long-wavelength fluorescence emission (670 nm) and large Stokes shift (180 nm). In concentration range of 0-30 μM, the probe was determined to react quickly with both Cys and GSH with low detection limits (<5 min, 35.2 nM for GSH and 34.8 nM for Cys) and achieve the sensitive fluorescence imaging of the biothiols located in the lysosomes of living cells.

De Novo Design of a Robust Fluorescent Probe for Basal HClO Imaging in a Mouse Parkinson's Disease Model

Elevated HClO gets involved in the pathogenesis of Parkinson's disease (PD). Herein, a novel fluorescent probe NUU-1 was designed and synthesized. Distinct from the general strategies, NUU-1 features two distinct HClO reactive sites, a HClO-specific reaction site and a HClO-nonspecific reactive site, which in turn endows NUU-1 with the "0 + 1 > 1" amplification effect, that thus dramatically promotes the selectivity. NUU-1 displayed a fast response rate (within 15 s), remarkable fluorescence enhancement (about 538-fold), and excellent sensitivity (LOD = 25.8 nM) in response to HClO while the remaining fluorescence silence toward other common ROS (H₂O₂, ^•OH, ONOO^-, O₂^•-, and ¹O₂) even at high concentrations (up to 0.5 mM). NUU-1 allows for the imaging of both exogenous and endogenous HClO in living dopaminergic cells (SH-SY5Y). Moreover, by employing NUU-1 as the probe, the image of HClO in C. elegans and zebrafish was successfully achieved. Significantly, in the first trial, NUU-1 was successfully utilized for the brain basal HClO imaging in PD mice models and distinguished PD brain tissues from normal control, thereby holding great potential for in-depth biological applications.

Research Progress of Small Molecule Fluorescent Probes for Detecting Hypochlorite

Hypochlorous acid (HOCl) generates from the reaction between hydrogen peroxide and chloride ions via myeloperoxidase (MPO)-mediated in vivo. As very important reactive oxygen species (ROS), hypochlorous acid (HOCl)/hypochlorite (OCl⁻) play a crucial role in a variety of physiological and pathological processes. However, excessive or misplaced production of HOCl/OCl⁻ can cause variety of tissue damage and human diseases. Therefore, rapid, sensitive, and selective detection of OCl⁻ is very important. In recent years, the fluorescent probe method for detecting hypochlorous acid has been developed rapidly due to its simple operation, low toxicity, high sensitivity, and high selectivity. In this review, the progress of recently discovered fluorescent probes for the detection of hypochlorous acid was summarized with the aim to provide useful information for further design of better fluorescent probes.

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.

A near-infrared fluorogenic probe with fast response for detecting sodium dithionite in living cells

Developing a reliable fluorescence probe is crucial for accurately monitoring sodium dithionite (Na₂S₂O₄, SDT) in biosystems, but the current reported azo-based ones suffers from short excitation/emission wavelengths and relative slow response speed. To address this issue, we herein present a novel near-infrared emissive fluorescence probe for SDT, namely DCM-MQ, consisting of a dicyanomethylene-benzopyran fluorogenic reporter and a 1-methylquinolinium as recognition moiety. On the basis of the specific reduction mechanism, DCM-MQ exhibited a rapid colorimetric and fluorescent recognition for SDT (less than 3 s) with large Stokes shift (112 nm) and high sensitivity (detection limit was 19 nM). The fluorescence imaging results demonstrate that DCM-MQ is competent for monitoring SDT in living systems.