Fluorescence probe for hypochlorous acid in water and its applications for highly lysosome-targetable live cell imaging

Glutathione Modified silicon-doped Carbon Quantum dots as a Sensitive Fluorescent Probe for ClO- Detection

A selective and sensitive fluorescence method for hypochlorite (ClO-) was designed using glutathione (GSH) modified silicon-doped carbon quantum dots (GSH@Si-CDs). Then a dual emission ratio fluorescence probe (RF-probe) was obtained based on carbodiimide-activated coupling reaction between GSH and Si-CDs. i.e., when the excitation wavelength was kept at 360 nm, the GSH@Si-CDs exhibited strong blue and weak yellow fluorescence at 430 and 580 nm. Meanwhile, the fluorescence of GSH@Si-CDs could be selectively quenched at 430 nm and enhanced at 580 nm in the presence of ClO-, and corresponding limit of detection (LOD) and linear range were measured to be 0.35 µM and 1.0-33.3 µM. The sensing mechanism of the system was also investigated in detail. Moreover, the RF-probe with good accuracy was successfully employed to monitor ClO- in real samples with satisfactory results compared to the standard iodometric method.

A G-quadruplex/thioflavin T-based label-free biosensor to detect ClO- in stress-induced hypertension

Hypochlorous acid (HClO), as an essential reactive oxygen species (ROS) in biological systems, plays a pivotal role in processes of physiology and pathology. Abnormal fluctuations in HClO concentration can lead to various diseases, such as inflammation, cardiovascular diseases, and neurodegeneration. Therefore, developing an approach to rapidly and sensitively quantify ClO- content is vital to biomedicine development and bioassays. Herein, we fabricated a novel "turn-on" label-free fluorescence DNA probe to specifically detect hypochlorite ion (ClO-) based on G-quadruplex formation. To this end, we designed a G-rich signal DNA sequence (S-DNA) and a block DNA sequence (B-DNA), followed by the introduction of ClO--responsive phosphorothioate (PS) into B-DNA. In the absence of ClO-, B-DNA hybridized with S-DNA, preventing G-quadruplex formation from S-DNA; this resulted in the relatively low fluorescence intensity of ThT. Once ClO- was added, the hydrolysis between PS and ClO- split the B-DNA into two fragments, resulting in B-DNA breaking away from S-DNA, allowing G-quadruplex formation from S-DNA and increasing the fluorescence intensity of ThT. Using this method, we can detect ClO- without the interference of additional reactive oxygen species. The detection limit of ClO- was as low as 10 nM. Furthermore, this method facilitates the detection of ClO- within the tissues of rats with stress-induced hypertension.

Recent Development of Lysosome-Targeted Organic Fluorescent Probes for Reactive Oxygen Species

Reactive oxygen species (ROS) are extremely important for various biological functions. Lysosome plays key roles in cellular metabolism and has been known as the stomach of cells. The abnormalities and malfunctioning of lysosomal function are associated with many diseases. Accordingly, the quantitative monitoring and real-time imaging of ROS in lysosomes are of great interest. In recent years, with the advancement of fluorescence imaging, fluorescent ROS probes have received considerable interest in the biomedical field. Thus far, considerable efforts have been undertaken to create synthetic fluorescent probes for sensing ROS in lysosomes; however, specific review articles on this topic are still lacking. This review provides a general introduction to fluorescence imaging technology, the sensing mechanisms of fluorescent probes, lysosomes, and design strategies for lysosome-targetable fluorescent ROS probes. In addition, the latest advancements in organic small-molecule fluorescent probes for ROS detection within lysosomes are discussed. Finally, the main challenges and future perspectives for developing effective lysosome-targetable fluorescent ROS probes for biomedical applications are presented.

BODIPY-Ethynylestradiol molecular rotors as fluorescent viscosity probes in endoplasmic reticulum

Due to their capability for sensing changes in viscosity, fluorescent molecular rotors (FMRs) have emerged as potential tools to develop several promising viscosity probes; most of them, however, localize non-selectively within cells, precluding changes in the viscosity of specific cellular microdomains to be studied by these means. Following previous reports on enhanced fluorophore uptake efficiency and selectivity by incorporation of biological submolecular fragments, here we report two potential BODIPY FMRs based on an ethynylestradiol spindle, a non-cytotoxic semisynthetic estrogen well recognized by human cells. A critical evaluation of the potential of these fluorophores for being employed as FMRs is presented, including the photophysical characterization of the probes, SXRD studies and TD-DFT computations, as well as confocal microscopy imaging in MCF-7 (breast cancer) cells.

Hypochlorous acid triggered fluorescent probes for in situ imaging of a psoriasis model

Psoriasis is a common skin disease with complex pathogenesis that lacks diagnostic methods. Typically, psoriasis is an inflammation-related disease accompanied by high expression of reactive oxygen species (ROS) in the infected part. However, due to the lack of suitable tools, it is difficult to identify the ROS, especially certain types of ROS (e.g., HOCl) in the psoriasis model. Here, two HOCl-specific fluorescent probes, G1 and G2, were designed and synthesized based on oxazine 1. Both probes could react with HOCl with high selectivity among other ROS under physiological conditions. The selected probe G2 could detect HOCl in HL-60 cells without special stimulation and detect endogenously produced HOCl in the mouse model of arthritis. Thus, G2 was used to identify and image HOCl in situ in the imiquimod induced psoriasis model. The result showed that HOCl was a potential pathological marker of psoriasis.

A Highly Selective Fluorescent Probe for Hypochlorous Acid in Living Cells Based on a Naphthalene Derivative

Hypochlorous acid (HOCl) was crucial for maintaining the homeostasis in cells and plays vital roles in many physiological and pathological processes. In this work, a highly selective fluorescent probe for hypochlorous acid in living cells was constructed and prepared based on a naphthalene derivative. A naphthalene derivative was utilized as the fluorescent group, and N,N-dimethylthiocarbamate was applied as the selective recognition site for HOCl. Before adding HOCl, the fluorescent probe exhibited weak fluorescence. Upon adding HOCl, the fluorescent probe displayed remarkable fluorescence enhancement. The fluorescence intensity at 502 nm showed a linear response to the concentration of HOCl from 3.0 × 10−7 to 1.0 × 10−5 mol·L−1. The detection limit was estimated to be 1.5 × 10−7 mol·L−1 for HOCl. The fluorescent probe showed fast response and outstanding selectivity toward HOCl. It owned good biocompatibility and had also been successfully applied in the confocal imaging of exogenous and endogenous HOCl in living cells.

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.

A selective fluorescence sensor for hypochlorite used for the detection of hypochlorite in zebrafish

Hypochlorite is used as a water disinfectant and it is also produced by biological organisms. Its detection and quantification is important and could lead to its mechanism of reactivity in cells. We have synthesized a new fluorescence sensor for hypochlorite based on bithiophene and furan-carbohydrazide. The sensor shows increased fluorescence as a function of hypochlorite and is selective for hypochlorite. Fluorescence enhancement due to hypochlorite is observed when the sensor is used in aqueous solutions at neutral pH values. Using the sensor, the detection limit for hypochlorite is 4.2 µM, making the sensor practical to determine hypochlorite in water. Applying the sensor to aide in the detection of hypochlorite in zebrafish, showed localization of ClO^-/HClO in the air bladders and eyes of zebrafish.

An Acridine-Based Fluorescent Sensor for Monitoring ClO- in Water Samples and Zebrafish

A novel acridine-based fluorescent chemosensor, BK ((E)-2-((acridine-9-ylimino)methyl)-N-benzhydrylhydrazine-1-carbothioamide), for monitoring ClO- was prepared. The sensor BK was synthesized by introducing a new synthetic route of making aldehyde group using formic hydrazide. Probe BK displayed notable fluorescence quenching in the presence of ClO- and showed a great selectivity over other guest analytes. The detection limit was calculated to be 7.65 μM. Additionally, BK was satisfactorily applied for sensing ClO- in water samples and zebrafish.

Design of long-wavelength emission carbon dots for hypochlorous detection and cellular imaging

A facile strategy for the preparation of nitrogen and phosphorus co-doped carbon dots (N, P-CDs) with long-wavelength emission is attractively proposed in one-pot hydrothermal strategy. The resulting N, P-CDs hold exceptional optical features and display excitation wavelength-independent properties with the emission wavelength at 590 nm, which enable it with the satisfactory relative quantum yield (QY) of 15.6% in long-wavelength region. In addition, the proposed N, P-CDs demonstrates specific selectivity towards ClO^- over other competitive reactive oxygen species and exhibits rapid fluorescence response time to ClO^-. Moreover, the N, P-CDs exhibits low-cytotoxicity and excellent cell membrane permeability for recognizing ClO^- in SMMC-7721 cells, which demonstrates their enormous potential in biological system.

Sensitive and selective fluorescent probe for hypochlorite in 100% aqueous solution and its application for lysosome-targetable cell imaging

A morpholine-functionalized pyrrole-cyanine probe was synthesized via a simple condensation reaction in high yield. This probe exhibits high selectivity toward ClO^- on fluorescence and UV-vis spectra in neat aqueous solution. The strong green emission of the probe solution was quenched and the yellow color faded immediately upon the addition of ClO^-. The detection limit of the probe for ClO^- was 0.165 μM. The mechanism of hypochlorite-induced CC breakage was supposed on the basis of EIS-MS, NMR, and density functional theory (DFT) calculation. Finally, the probe was utilized to image ClO^- in lysosomes of living cells.

Peptide-capped functionalized Ag/Au bimetal nanoclusters with enhanced red fluorescence for lysosome-targeted imaging of hypochlorite in living cells

Bioimaging probes for monitoring intracellular reactive oxygen species have important implications for cell biology research. Herein, we developed peptide-capped silver/gold nanoclusters (peptide@Ag/Au NCs) for lysosome-targeted imaging of hypochlorite (ClO^-). The peptide@Ag/Au NCs were synthesized via a one-pot method using peptide as both a template and a reducing agent. The fluorescence intensity and absolute quantum yield of peptide@Ag/Au NCs were much higher than those of peptide-capped gold nanoclusters and silver nanoclusters. In the presence of ClO^-, the fluorescence of peptide@Ag/Au NCs was quenched, accompanied by a redshift due to ClO^--induced oxidation of the peptide ligand and decreased Ag content in Ag/Au NCs. The relative fluorescence intensity F₀/F had favourable linearity for ClO^- concentrations in the range 0.1-100 μmol/L (R² = 0.9954), with a detection limit (LOD) of 80 nmol/L. The lysosome-targeted peptide@Ag/Au NCs were applied to detect ClO^- in lysosomes in living cells via fluorescence imaging.

Mitochondria-targeting turn-on fluorescent probe for HClO detection and imaging in living cells

Hypochlorous/hypochlorite (HClO/ClO^-), one of the most important signal molecule, plays a crucial role in many cellular signaling pathways. It is reported that the HClO/ClO^- level in mitochondria is important to maintain the normal mitochondrial function. Herein, we present two simple fluorescent probes BAC and mitochondria-targeting fluorescent probe TACB for the detection of ClO^-. Probes BAC &TACB could be sensitively and selectivity detecting ClO^- at the nanomolar levels with the detection limit of 1.64 × 10^-9 M and 9.86 × 10^-8 M, respectively. Additionally, probes BAC &TACB with the response unit of CO moiety could selectively detect ClO^- over other various analytes such as anions, metal ions and OH, ¹O₂, H₂O₂. The response time of probe TACB for ClO^- (<20 s), implying that it could offer a real-time analytical assay of ClO^-. Finally, probe BAC was used for monitoring the ClO^- in HEK293T cells and probe TACB could be utilized to track the fluctuations of exogenous ClO^- levels in the mitochondria of Hela cells.

A near-infrared fluorescent probe based on a novel rectilinearly π-extended rhodamine derivative and its applications

A novel NIR fluorescent probe RQNA based on a π-extended rhodamine derivative RQN for the specific detection of mitochondrial Cu²⁺ has been synthesized.

Novel near-infrared fluorescent probe with a large Stokes shift for sensing hypochlorous acid in mitochondria

A novel mitochondria-targeted fluorescent probe, MXS, with a large Stokes shift (130 nm) based on a xanthene-hemicyanine dyad structure, has been successfully designed and synthesized for the specific detection of HOCl.

A mitochondria-targeted fluorescent probe for hypochlorite sensing and its application in bioimaging

A coumarin-diaminomaleonitrile derivative was prepared and used for detecting OCl⁻ in living cells and zebrafish. Its high selectivity, sensitivity and low toxicity indicate that it is an ideal tool for biological applications.

Novel rhodamine dye with large Stokes shifts by fusing the 1,4-diethylpiperazine moiety and its applications in fast detection of Cu2+

Rhodamine dyes were widely developed for designing probes due to their excellent photophysical properties and biocompatibility. However, traditional rhodamine dyes still bear major drawbacks of short emission wavelengths (<600 nm) and narrow Stokes shifts (<30 nm), which limit their biological imaging applications. Herein, we reported a novel mitochondria-targeted fluorescent dye JRQ with near-infrared (NIR) emission wavelength and improved Stokes shift (63 nm) by tuning the donor–acceptor–donor (D–A–D) character of the rhodamine skeleton. As expected, JRQ exhibited multiple excellent properties and could accumulate in mitochondria, and can therefore be used as a signal reporter for the design of fluorescent probes by taking advantage of the fluorescence controlled mechanism of the ring opening and closing chemical processes of the spirolactone platform. By using JRQ as a precursor, a highly sensitive fluorescent probe JRQN for the fast detection of mitochondrial Cu²⁺ ions was synthesized based on the Cu²⁺-triggered specific hydrolysis mechanism because mitochondria are an important reservoir of intracellular Cu²⁺. We expect that the Stokes shift increase of rhodamine dyes via tuning the donor–acceptor–donor (D–A–D) character of the rhodamine skeleton will provide a novel synthetic approach for the development of rhodamine dyes and expansion of their applications.

A novel NIR rhodamine dye JRQ with large Stokes shift (70 nm) by fusing the 1,4-diethylpiperazine moiety in rhodamine dyes has been synthesized and utilized to design a probe.

Rational modulation of coumarin–hemicyanine platform based on OH substitution for higher selective detection of hypochlorite

A NIR and ratiometric fluorescent probe was developed to quantitate arthritis-dependent HOCl production in vivo with high selectivity and sensitivity.

A near-infrared ratiometric fluorescent probe based on the CN double bond for monitoring SO2 and its application in biological imaging

A near-infrared ratiometric fluorescent probe based on CN double bond was developed for monitoring SO₂ and its application in biological imaging.

A new ratiometric fluorescent probe for sensing lysosomal HOCl based on fluorescence resonance energy transfer strategy

In this paper, ratiometric imaging of lysosomal HOCl was realized with a molecular probe (CR-Ly) based on fluorescence resonance energy transfer by using coumarin as the donor and rhodamine as acceptor. CR-Ly showed high sensitivity and fast response to HOCl. Moreover, CR-Ly exhibited excellent selectivity and sensitivity for HOCl over other biologically relevant species. Furthermore, it was successfully utilized to image the endogenous HOCl with low cytotoxity. And CR-Ly was capable of targeting lysosomes and monitoring lysosomal hypochlorous acid changes owing to the presence of the morpholine moiety. We believe that probe CR-Ly would be helpful to further research on the HOCl-associated diseases in lysosomes.

A lysosome-targetable and ratiometric fluorescent probe for hypochlorous acid in living cells based on a 1,8-naphthalimide derivative

Hypochlorous acid (HClO) is an important reactive oxygen species (ROS) and plays a significant role in living organisms. Highly selective and lysosome-targetable probes for sensing hypochlorous acid are rare. In this article, we designed and prepared a new lysosome-targeting and ratiometric fluorescent probe for monitoring the levels of hypochlorous acid. 4-Aminonaphthalimide was chosen as the fluorescent group and (2-aminoethyl) thiourea group was used as a specific recognition group for HClO. A morpholine unit was employed as a lysosome-targeting group. In the absence of HClO the probe underwent intramolecular charge transfer (ICT) and showed a green emission. When excess HClO is present, the ICT process was interrupted which caused a 57 nm blue-shift of fluorescence emission from 533 nm to 476 nm. The ratiometric fluorescent probe showed outstanding selectivity toward HClO over other various bioactive species. Furthermore, the ratiometric fluorescent probe exhibited rapid response time and ability of working in a wide pH range. The linear response of I_476nm/I_533nm toward HClO was obtained in a concentration range of HClO from 1.0 × 10^-6 to 1.0 × 10^-4 mol·L^-1. The detection limit was estimated to be 8.0 × 10^-7 mol·L^-1 for HClO. Moreover, the probe showed a perfect lysosome-targeting ability, and has been successfully used to the confocal imaging of HClO in lysosomes of HepG2 cells with little cell toxicity. All of such good properties illustrated that it could be applied to determine HClO at lysosomes in living cells.

A lysosome specific theranostic NO donor inhibits cancer cells by stimuli responsive molecular self-decomposition with an on-demand fluorescence pattern

The anticancer mechanism of NO is difficult to study owing to its short lifetime and high reactivity. Thus, a theranostic anticancer NO donor assembled with NO on-demand release abilities, accurate lysosome location capabilities and signal feedback behavior was developed. Profiting from the theranostic properties, the specific mechanism was comprehensively studied. Spectral and cell imaging studies revealed that the as prepared NO donors could release NO in solution or within cancer cells. Fluorescence co-dyeing experiments demonstrated that Mo-Nap-NO entered lysosomes specifically and disrupted them after being triggered by light. Upon irradiation with 460 nm visible light, both the donors demonstrated considerable in vitro anticancer effects. A further mechanistic study showed that after entering the lysosome and being triggered by 460 nm irradiation, NO ruptured the lysosome, resulting in the release of cathepsin D into the cytosol, which activated the caspase3 mediated apoptosis pathway.

Development of a Concise Rhodamine-Formylhydrazine Type Fluorescent Probe for Highly Specific and Ultrasensitive Tracing of Basal HOCl in Live Cells and Zebrafish

Hypochlorous acid (HOCl) has received special attention by virtue of its pivotal antimicrobial nature, and the appropriate amount of HOCl is beneficial to innate immunity of host to cope with microbial invasion. However, the uncontrollable accumulation of HOCl is implicated in many human diseases and even cancers. Thus, to determine its deeper biological functions, it is significantly important to specifically monitor intracellular HOCl in biosystems. Herein, we rationally designed a simple fluorescent probe FH-HA on the basis of the formylhydrazine recognition receptor and rhodamine B fluorophore. It is worth noting that the formylhydrazine moiety for the first time is adopted as the recognition receptor for specifically recognizing HOCl. Additionally, probe FH-HA also exhibited excellent performance in many areas including satisfactory water-solubility, high specificity, and excellent sensitivity. Notably, probe FH-HA could quickly respond to HOCl (within 3 s), which facilitates the tracing of transient HOCl. More importantly, probe FH-HA was capable of specifically tracing the fluctuations of endogenous HOCl in living cells and zebrafish, and it could monitor basal HOCl in cancer cells to distinguish cancer cells from normal ones.

Rapid and visual detection for hypochlorite of an AIE enhanced fluorescence probe

In this paper, a new 'turn-on' fluorescence probe for the rapid, sensitive, and visual detection of hypochlorite is reported. The push-pull type trianiline-tricyanofuran-based fluorescent probe was prepared using a condensation reaction between tricyanofuran and the thiophene-trianiline derivative that had high quantum yields and showed aggregation-induced emission enhanced properties. Upon exposure to hypochlorite, prominent fluorescence enhancement of the probe was observed via the release of the fluorophore from the probe. The probe showed a ratiometric absorption change at 315 nm and 575 nm. Importantly, the probe showed an excellent detection limit for hypochlorite at 1.2 × 10^-7  M in solution and it was successfully applied for monitoring hypochlorite in waste water by test strip. This work reports a new fluorescence analytical sensing method for hypochlorite that has potential practical value in environmental monitoring and biological discrimination.

Two coumarin-based turn-on fluorescent probes based on for hypochlorous acid detection and imaging in living cells

This work, two turn-on fluorescent probes (3-acetyl-2H-chromen-2-one (ACO) & (1E)-1-(1-(2-oxo-2H-chromen-3-yl)ethylidene)thiosemicarbazide (CETC)) based on coumarin have been designed and synthesized, which could selectively and sensitively recognize ClO^- with fast response time. ACO &CETC were almost non fluorescent possibly due to both the lacton form of coumarin and unbridged CN bonds which can undergo a nonradiative decay process in the excited state. Upon the addition of ClO^-, ACO &CETC were oxidized to ring - opened by cleavage the CO and CN and the fluorescence intensity were increased considerably. Fluorescence titration experiments showed that the detection limit ACO &CETC is as low as 22 nm and 51 nm respectively. In particular, some relevant reactive species, including OH, ¹O₂, H₂O₂, KO₂, some anions and cations cannot be interference with the test. In live cell experiments, ACO &CETC were successfully applied to image exogenous ClO^- in HepG2 cells. Therefore, ACO &CETC not only could image ClO^- in living cells but also proved that CO and CN can be cleavage by ClO^-.

A mitochondria-targeted near-infrared fluorescent probe with a large Stokes shift for real-time detection of hypochlorous acid

A real-time mitochondria-targeted near-infrared fluorescent probeLhas been synthesized with large Stokes shifts, and high selectivity and sensitivity.

An ultra-sensitive ratiometric fluorescent probe for hypochlorous acid detection by the synergistic effect of AIE and TBET and its application of detecting exogenous/endogenous HOCl in living cells

TR-OClexhibits ultra-high sensitivity towards HOCl with a 7000-fold enhancement in the fluorescence ratio (I₅₈₉/I₄₇₇) and a detection limit of 1.29 nM, which is one of the highest recorded so far.

A near-infrared fluorescent probe based on photostable Si-rhodamine for imaging hypochlorous acid during lysosome-involved inflammatory response

Hypochloric acid (HClO) is mainly distributed in acidic lysosomes of phagocytes and closely associated with numerous physiological and pathological processes, especially inflammatory response. Fluorescent probe has become an important tool for imaging HClO in lysosomes, but suffered from interference from autofluorescence in vivo, phototoxicity to biosamples and photobleaching phenomenon due to their short-wavelength excitation and emission. Unfortunately, up to now, no near-infrared (NIR) lysosome-targetable fluorescent probe has been reported for imaging HClO. In this paper, a near-infrared fluorescent probe Lyso-NIR-HClO for imaging lysosomal HClO was reported for the first time. Lyso-NIR-HClO based on Si-rhodamine is consisted of a morpholine unit as a lysosome-targetable group and a HClO-mediated cyclization reaction site as a response group, which was applied for highly selective and sensitive detection and imaging for endogenous and exogenous HClO in lysosomes, with a linear range from 5.0 × 10^-8 to 1.0 × 10^-5 M and a detection limit of 2.0 × 10^-8 M in vitro. Attributed to NIR emission and excellent photostability of Si-rhodamine, Lyso-NIR-HClO exhibits excellent performances in vivo, such as low interference from intracellular autofluorescence, stable and persistent fluorescence signal and good tissue penetration, which are in favor of accurate, time-lapse and long-term imaging for HClO. Finally, we applied the probe Lyso-NIR-HClO to visualize endogenous HClO during lysosome-involved inflammatory response including bacteria-infected cells and inflamed mouse model with satisfactory results. The above results proved that Lyso-NIR-HClO would be a potentially useful tool for the study of biological functions and pathological roles of HClO in lysosomes, especially role of lysosome in the inflammatory response.

Mitochondria and lysosome-targetable fluorescent probes for HOCl: recent advances and perspectives

Hypochlorous acid (HOCl), as one of the reactive oxygen species (ROS), plays an important role in the destruction of pathogens in the immune system. However, abnormal concentration of biogenic HOCl can also damage host tissues, and it has been shown to be associated with many diseases. Accordingly, detection of HOCl at the subcellular level is important for understanding inflammation and cellular apoptosis. Toward this end, in the past few years, a wide variety of fluorescent HOCl probes have been engineered and applied for imaging of HOCl in subcellular organelles. In this review, we highlight the representative cases of the fluorescent HOCl probes with mitochondria and lysosome-targetable ability. The discussion includes their design strategies, sensing mechanisms, and applications in bio-imaging of HOCl in mitochondria and lysosomes.

Synthesis and bioapplication of a highly selective and sensitive fluorescent probe for HOCl based on a phenothiazine–dicyanoisophorone conjugate with large Stokes shift

A fluorescent probe with a large Stokes shift for monitoring endogenous HOCl in living cells has been prepared.

Water solubility is essential for fluorescent probes to image hypochlorous acid in live cells

Our findings, for the first time, highlight the importance of water-solubility of fluorescent probes for HClO imaging.

Lysosomal-Targeted Two-Photon Fluorescent Probe to Sense Hypochlorous Acid in Live Cells

A two-photon reversible fluorescent probe L1 was designed and synthesized. The fluorescence intensity of the probe solution was strong, while the fluorescence of the solution was obviously quenched and the color of the solution was changed after the addition of hypochlorous acid, indicating this is "naked-eye sensor" for the detection of HClO. The probe showed great selectivity for hypochlorous acid over other reactive oxygen species (ROS) and anions. Fluorescence titration experiments showed that the probe has a low detection limit of 0.674 μM. Because of a morpholine group introduced to the naphathalimide framework, probe L1 was successfully applied to detect intracellular HClO in lysosome.

Ratiometric imaging of lysosomal hypochlorous acid enabled by FRET-based polymer dots

FRET-based fluorescent polymer dots (FPD) with good membrane permeability have been developed for ratiometric imaging of lysosomal HClO in living cells.