A BODIPY aldoxime-based chemodosimeter for highly selective and rapid detection of hypochlorous acid

A dual-responsive ratiometric fluorescent probe for the detection of hypochlorite and hydrazine in environmental samples, live cells, and plant tissues

Hypochlorite (ClO-), a potent oxidizer and disinfectant, and hydrazine, a powerful reducing agent, are widely used in daily life and various industries. However, their extensive use comes with significant risks, as they are highly toxic to both the environment and human health. They have been associated with various health issues and even linked to cancer. Therefore, the simultaneous detection of hypochlorite and hydrazine is crucial for assessing their impact and monitoring the onset and progression of related diseases. A phenanthroimidazole-indandione based colorimetric and ratiometric fluorescent probe PIID was designed and synthesized for dual channel detection of hypochlorite and hydrazine in environmental and biological samples. Probe PIID, which showed a strong yellow-orange emission at 640 nm with a massive Stokes shift of 220 nm, exhibited excellent fluorescence change from yellow-orange to green (526 nm) in the presence of ClO- and from yellow-orange to blue (424 nm) in the presence of hydrazine in an aqueous-THF solvent system. A strong ICT effect, which was acting in probe PIID, gets weakened through ClO- - mediated cleavage of the CC bridge bond to produce aldehyde PIB with a blue shift of 114 nm and hydrazine-induced hydrazinolysis of the indanedione moiety to form hydrazone compound PIBH with a blue shift of 216 nm and that was also confirmed by DFT studies. Not only that, the probe exhibits excellent selectivity over other ROS (reactive oxygen species) and amines with a very fast response time of 40 seconds for hypochlorite and 90 seconds for hydrazine, and high sensitivity was observed with detection limits of 32.75 nM for hypochlorite and 92 nM for hydrazine. Moreover, PIID was employed to monitor both the analytes successfully in environmental water samples and in a solid-state TLC strip study. Hypochlorite was monitored in commercial disinfectants, and by exogenous bioimaging in human breast cancer cells (MDA-MB 231) and endogenous bioimaging in RAW 264.7 macrophage cells with very low cytotoxicity and good cell viability. Meanwhile, hydrazine was tracked in soil samples, and confocal imaging was performed on onion tissue.

Two-Photon Cellular and Intravital Imaging of Hypochlorous Acid by Fluorescent Probes That Exhibit a Synergistic Excited-State Intramolecular Proton Transfer-Intramolecular Charge Transfer Mechanism Enabling Near-Infrared Emission with a Large Stokes Shift

To develop highly effective molecular tools for intravital imaging of hypochlorous acid (HOCl), in this study, we initially designed two-photon hybrid fluorophores, SDP and P-SDP, by conjugating the classical dye 2-(2'-hydroxyphenyl)benzothiazole with the two-photon hydroxylphenyl-butadienylpyridinium fluorophore. The designed fluorophores exhibit a synergistic interaction between excited-state intramolecular proton transfer and intramolecular charge transfer mechanisms, enabling near-infrared (NIR) emission and significant Stokes shifts. Subsequently, using these fluorophores, we developed two HOCl fluorescent probes, SDP-SN and P-SDP-SN, by further incorporating N,N-dimethylthiocarbamate as a specific recognition group for HOCl. Toward HOCl, both SDP-SN and P-SDP-SN demonstrate an ultrafast response (less than 3 s), NIR emission at wavelengths of 714 and 682 nm, and remarkable Stokes shifts of 303 and 271 nm, respectively. Leveraging these advantages in conjunction with their ability to cross the blood-brain barrier, the probes find successful application in two-photon cellular and intravital imaging of HOCl. This includes visualizing endogenous generation of HOCl in cellular models related to inflammation, hyperglycemia, and ferroptosis, as well as mapping in vivo generation of HOCl within the brain and abdominal cavity using a murine model of systemic inflammation.

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.

A novel thienothiophene-based "dual-responsive" probe for rapid, selective and sensitive detection of hypochlorite

BACKGROUND

Hypochlorite/hypochlorous acid (ClO-/HOCl) is a biologically crucial reactive oxygen species (ROS), produced in living organisms and has a critical role as an antimicrobial agent in the natural defense system. However, when ClO- is produced excessively, it can lead to the oxidative damage of biomolecules, resulting in organ damage and various diseases. Therefore, it is imperative to have a straightforward, quick and reliable method for over watching the minimum amount of ClO- in different environments.

RESULTS

Herein, a new probe TTM, containing thienothiophene and malononitrile units, was developed for exceptionally selective and sensitive hypochlorite (ClO-) detection. TTM demonstrated a rapid "turn-on" fluorescence response (<30 s), naked-eye detection (colorimetric), voltammetric read-out with anodic scan, low detection limit (LOD = 0.58 μM and 1.43 μM for optical and electrochemical methods, respectively) and applicability in detecting ClO- in real water samples and living cells.

SIGNIFICANCE AND NOVELTY

This study represents one of the rare examples of a small thienothiophene-based molecule for both optical and electrochemical detections of ClO- in an aqueous medium.

A ratiometric small-molecule fluorescent probe for the selective detection of hypochlorite by an oxidative cyclization reaction: application to commercial disinfectants and live cells

A highly selective thiophene-thioimidazole hydrazine-based ratiometric chemodosimeter (TPBN) was designed and synthesized to detect hypochlorite (ClO-). The probe showed yellow fluorescence and exhibited ultra sensitivity towards hypochlorite (detection limit 8.74 nM) through the oxidative intramolecular cyclization process to give a blue fluorescent triazole product (TPBN-P). Additionally, the as-designed sensor displayed a fast response (80 s) to hypochlorite with excellent selectivity over other competing analytes. DFT calculations, ESI-MS, and 1H NMR titration experiments supported the detection mechanism. The probe was a valuable and practical ratiometric sensor for test strips, commercial disinfectants, and water samples. The probe was successfully used in the bio-imaging of hypochlorite in human breast cancer cells due to its noteworthy photophysical characteristics and good cell permeability.

A Lipid Droplet-Specific NIR Fluorescent Probe with a Large Stokes Shift for In Vivo Visualization of Polarity in Contrast-Induced Acute Kidney Injury

The research on lipid droplets (LDs) has attracted great attention in the field of biomedical science in recent years. LD malfunction is found to be associated with the development of acute kidney injury (AKI). To monitor this biological process and explain related pathological behavior, the development of excellent LD fluorescent probes with a polarity-sensitive character would provide a desirable strategy. Herein, we designed a new polarity-susceptible fluorescent probe named LD-B with LD targetability, which exhibits very weak fluorescence in highly polar solvents based on the twisted intramolecular charge transfer effect but enhanced fluorescence in low polar environments, enabling us to visualize polarity alteration. The probe LD-B also possesses the merits of intense near-infrared (NIR) emission, good photostability, large Stokes shift, low toxicity, faster metabolic rate, and wash-free ability; thereby, it would contribute to efficient LD fluorescence visualization application. Using LD-B via confocal laser scanning fluorescence imaging and a small-animal imaging system in vivo, we first manifested a prominent rise of LD polarity in contrast-induced AKI (CI-AKI), not only at the cellular level but also in animals in vivo. Furthermore, the in vivo studies suggest that LD-B could accumulate in the kidney. In addition, the normal cell lines (including kidney cells) exhibiting a greater polarity of LDs than the cancer cells have been demonstrated systemically. Altogether, our work presents an effective approach for the medical diagnosis of LDs related to CI-AKI and identification of potential therapeutic markers.

Monitoring of Hypochlorite Level in Fruits, Vegetables, and Dairy Products: A BODIPY-Based Fluorescent Probe for the Rapid and Highly Selective Detection of Hypochlorite

Hypochlorite/hypochlorous acid (ClO^-/HOCl), among the diverse reactive oxygen species, plays a vital role in various biological processes. Besides, ClO^- is widely known as a sanitizer for fruits, vegetables, and fresh-cut produce, killing bacteria and pathogens. However, excessive level of ClO^- can lead to the oxidation of biomolecules such as DNA, RNA, and proteins, threatening vital organs. Therefore, reliable and effective methods are of utmost importance to monitor trace amounts of ClO^-. In this work, a novel BODIPY-based fluorescent probe bearing thiophene and a malononitrile moiety (BOD-CN) was designed and constructed to efficiently detect ClO^-, which exhibited distinct features such as excellent selectivity, sensitivity (LOD = 83.3 nM), and rapid response (<30 s). Importantly, the probe successfully detected ClO^- in various spiked water, milk, vegetable, and fruit samples. In all, BOD-CN offers a clearly promising approach to describe the quality of ClO^--added dairy products, water, fresh vegetables, and fruits.

Two novel fluorescent probes based on quinolinone for continuous recognition of Al3+ and ClO. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023;300:122917. [PMID: 37269662 DOI: 10.1016/j.saa.2023.122917]

On the basis of classical Schiff base reaction, two novel and efficient fluorescent probes (DQNS, DQNS1) were designed and synthesized by introducing Schiff base structure into dis-quinolinone unit for structural modification, which can be used to detect Al³⁺ and ClO^-. Because the power supply capacity of H is weaker than that of methoxy, DQNS shows better optical performance: a large Stokes Shift (132 nm), identify Al³⁺ and ClO^- with high sensitivity and selectivity, low detection limit (29.8 nM and 25 nM) and fast response time (10 min and 10 s). Through the working curve and NMR titration experiment, the recognition mechanism of Al³⁺ and ClO^- (PET and ICT) probes are confirmed. Meanwhile, it is speculated that the probe has continuity for the detection of Al³⁺ and ClO^-. Furthermore, DQNS detection of Al³⁺ and ClO^- was applied to real water samples and living cell imaging.

Novel Near-Infrared Iridium(III) Complex for Chemiluminescence Imaging of Hypochlorous Acid

Chemiluminescence (CL) probes that possess near-infrared (NIR) emission are highly desirable for in vivo imaging due to their deeper tissue penetration ability and intrinsically high sensitivity. Herein, a novel iridium-based CL probe (NIRIr-CL-1) with direct NIR emission was reported as the result of hypochlorous acid (HClO)-initiated oxidative deoximation. To improve its biocompatibility and extend the CL time for in vivo imaging applications, this NIRIr-CL-1 was prepared as a CL nanoparticle probe (NIRIr-CL-1 dots) through encapsulation by an amphiphilic polymer Pluronic F127 (F127). All results demonstrate that the NIRIr-CL-1 dots have good selectivity and sensitivity for visualization of HClO even at the depth of 1.2 cm. Owing to these advantages, the CL imaging of exogenous and endogenous HClO in mice was achieved. This study could provide new insights into the construction of new NIR emission CL probes and expand their applications in biomedical imaging.

A unique triple-channel fluorescent probe for discriminative detection of cyanide, hydrazine, and hypochlorite

Herein, the first triple-channel fluorescent probe, TTB, excited at the same wavelength (λ_ex = 360 nm) in the same sensing medium for the detection and discrimination of cyanide, hydrazine, and hypochlorite, is disclosed. While a fluorescent white color appeared (λ_em = 470 nm) with the addition of cyanide ion into the probe solution, upon addition of hydrazine and hypochlorite, green (λ_em = 503 nm) and orange (λ_em = 585 nm) fluorescent colors, respectively, were observed. A naked-eye detection for the three ions was documented. With the appearance of orange color, a mega Stokes shift of 175 nm was observed. The probe exhibited excellent selectivity and lower detection limits of 0.24 μM, 4.1 nM and 0.27 μM, and dynamic ranges of 0.0-2.0 μM, 0.0-0.05 μM and 0.0-2.0 μM for cyanide, hydrazine and hypochlorite, respectively. The sensing mechanism was investigated through computational studies before and after the addition of cyanide, hypochlorite, and hydrazine, applying density functional theory (DFT), along with the calculation of optical properties by time-dependent DFT (TD-DFT) method. The results were found to be in good agreement with the experimental values. Remarkably, the probe, TTB, successfully detected cyanide, hydrazine, and hypochlorite in complex water samples. Moreover, the detection of cyanide was successfully performed in apricot kernels, as well as hypochlorite in fruits and vegetables.

Fluorescent phenothiazine-fused boron complexes for ratiometric hypochlorite imaging

Fluorescent hypochlorite probes with ratiometric imaging ability are highly desirable for imaging hypochlorite in biological systems. However, it is still challenging to develop new scaffolds for these probes. In this study, we demonstrate that phenothiazine-fused boron complexes are promising scaffolds for the design of ratiometric fluorescent hypochlorite probes. The synthesized complexes based on the scaffold show ultrafast and ratiometric absorption/fluorescence changes for hypochlorite. We also developed an endoplasmic reticulum-targeting probe and demonstrated that it has excellent real-time imaging ability for both endogenous and exogenous hypochlorite in the endoplasmic reticulum of living cells.

A Hydroxytricyanopyrrole-Based Fluorescent Probe for Sensitive and Selective Detection of Hypochlorous Acid

Hypochlorous acid (HOCl) is a reactive substance that reacts with most biomolecules and is essential in physiological and pathological processes. Abnormally elevated HOCl levels may cause inflammation and other disease responses. To further understand its key role in inflammation, HOCl must be detected in situ. Here, we designed a hydroxytricyanopyrrole-based small-molecule fluorescent probe (HTCP-NTC) to monitor and identify trace amounts of HOCl in biological systems. In the presence of HOCl, HTCP-NTC released hydroxyl groups that emit strong fluorescence covering a wide wavelength range from the visible to near-infrared region owing to the resumption of the intramolecular charge transfer process. Additionally, HTCP-NTC demonstrated a 202-fold fluorescence enhancement accompanied by a large Stokes shift and a low detection limit (21.7 nM). Furthermore, HTCP-NTC provided a rapid response to HOCl within 18 s, allowing real-time monitoring of intracellular HOCl. HTCP-NTC exhibited rapid kinetics and biocompatibility, allowing effective monitoring of the exogenous and endogenous HOCl fluctuations in living cells. Finally, based on fluorescence imaging, HTCP-NTC is a potential method for understanding the relationship between inflammation and HOCl.

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.

Sensing Hypochlorite or pH variations in live cells and zebrafish with a novel dual-functional ratiometric and colorimetric chemosensor

Both HClO and pH are essential players in multiple biological processes, which thus need to be controlled properly. Dysregulated HClO or pH correlates with many diseases. To meet these challenges, we need to develop highly competent probes for monitoring them. Over the years, despite a rich history of the development of HClO or pH probes, those that can do both jobs are still deficient. Herein, we present a novel dual-functional chemosensor, CMHN, which exhibits a blue and red shift of its fluorescence emission upon reacting with HClO or OH^-, respectively. CMHN was successfully harnessed in the imaging detection of HClO or OH^- in aqueous solutions, live cells, and zebrafish. Results indicated CMHN can detect HClO with high sensitivity (LOD -132 nM), a quick response time (<70 s), and high selectivity over dozens of interfering species through a colorimetric and ratiometric response. Besides, CMHN can probe pH changes sensitively and reversibly. Its working mechanism was verified by DFT calculations. These superior features make CMHN excel among the HClO or pH probes reported so far. Taken together, CMHN replenishes the deficiency in currently developed HClO or pH probes and paves the way for developing multifunctional HClO or pH probes in the future.

Oxime as a general photocage for the design of visible light photo-activatable fluorophores

Photoactivatable fluorophores have been widely used for tracking molecular and cellular dynamics with subdiffraction resolution. In this work, we have prepared a series of photoactivatable probes using the oxime moiety as a new class of photolabile caging group in which the photoactivation process is mediated by a highly efficient photodeoximation reaction. Incorporation of the oxime caging group into fluorophores results in loss of fluorescence. Upon light irradiation in the presence of air, the oxime-caged fluorophores are oxidized to their carbonyl derivatives, restoring strong fluorophore fluorescence. To demonstrate the utility of these oxime-caged fluorophores, we have created probes that target different organelles for live-cell confocal imaging. We also carried out photoactivated localization microscopy (PALM) imaging under physiological conditions using low-power light activation in the absence of cytotoxic additives. Our studies show that oximes represent a new class of visible-light photocages that can be widely used for cellular imaging, sensing, and photo-controlled molecular release.

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.

Theoretical Study of a Two-Photon Fluorescent Probe Based on Nile Red Derivatives with Controllable Fluorescence Wavelength and Water Solubility

Hypochloric acid (HOCl) plays a vital role in the natural defense system, but abnormal levels of it can cause cell damage, accelerated human aging, and various diseases. It is of great significance to develop new probes for detecting HOCl in biosystems nondestructively and noninvasively. The purpose of this work is to explore new chemical modification strategies of two-photon excitation fluorescence (TPEF) probes to improve the poor water solubility and low efficiency in imaging applications. Nil-OH-6 has a two-photon absorption cross-section value as high as 243 GM and attains a good quantum yield of 0.49. In addition, the modification of terminal groups with different azetidine-heterospirocycles or N,N-dialkyl fused amino groups to Nile Red can effectively improve the fluorescence efficiency as well as increase the solubility to some extent. This study provides some strategies to simultaneously improve the fluorescence performance and solubility of these two-photon probes and, hence, reliable guidance and a foundation for the subsequent synthesis of TPEF probes based on Nile Red.

Detection of hypochlorous acid fluctuation via a selective fluorescent probe in acute lung injury cells and mouse models

Acute lung injury (ALI) is a diffuse inflammatory pulmonary damage caused by excessive ROS that break the coordination of normal physiological structures and functions. Hypochlorous acid (HOCl), one kind of ROS, is a hopeful biological marker for inflammation-related diseases. Therefore, the excessive generation of HOCl might be a significant reason for oxidative injury in ALI. Herein, we developed a fluorescent probe, namely BCy-HOCl, for quantitatively monitoring and visualizing HOCl in living cells and in vivo. The probe BCy-HOCl displayed a significant fluorescence signal enhancement towards HOCl with excellent selectivity and sensitivity. The variation of HOCl in the ALI cell model and ALI mouse model was evaluated with BCy-HOCl to clarify the relationship between ALI and HOCl. Our results verified that the HOCl levels conspicuously increased with the severity of the ALI. Thus, HOCl is likely to play a crucial part in the process of ALI, which will probably provide a new strategy for its treatment.

A highly sensitive, fast responsive and reversible naphthalimide-based fluorescent probe for hypochlorous acid and ascorbic acid in aqueous solution and living cells

It is very important to exploit real-time, ultrasensitive and specific visualization detection methods for hypochlorous acid/hypochlorite (HOCl/ClO^-) in biological systems as they are the guardians of the human immune system against pathogens invasion. In our work, we designed a novel reversible naphthalimide-based fluorescent probe NAP-OH to recognize HClO/ClO^- with a unique selective colorimetric and fluorescent response, a short response time (<8 s) and a high sensitivity (10.3 nM). In addition, NAP-OH exhibits a novel on-off-on fluorescence response to ClO^-/ascorbic acid (AA) with good cycle stability. The fluorescence signal is quenched because HClO/ClO^- oxidizes the subunit of NAP-OH to the segment 2,2,6,6-tetramethyl-1-oxo-piperidinium in NAP-O, which can be reduced by AA with the recovery of fluorescence. Finally, the confocal fluorescence imaging has been performed, which proves that NAP-OH can satisfactorily monitor intracellular endogenous and exogenous HClO/AA redox cycles.

Malononitrile as the 'double-edged sword' of passivation-activation regulating two ICT to highly sensitive and accurate ratiometric fluorescent detection for hypochlorous acid in biological system

Hypochlorous acid (HOCl) as one of the most important reactive oxygen species in the organism, its role is more and more recognized. In fact, in recent years, various HOCl fluorescent probes have been developed unprecedentively based on various mechanisms. However, because most of the mechanisms are based on the oxidation characteristics of HOCl, the excellent detection performance of probes depends on the activation ability of some functional groups to reaction sites. The C[bond, double bond]C bond in the probe is often oxidized by HOCl to realize HOCl detection. However, due to the break of conjugated structure, the probe often present as a quenchable or turning on fluorescence emission. In this work, malononitrile was introduced as the "double-edged sword" of passivation-activation when in HOCl fluorescent probe was designed. Passivation-activation regulated two ICT (Intermolecular Charge Transfer, ICT) processes to ratiometric fluorescent detection for HOCl. Highly sensitive and accurate detection realized efficient application in biological imaging.

Multimodal Imaging Iridium(III) Complex for Hypochlorous Acid in Living Systems

Biomolecule tracing with different imaging methods is of great significance for more accurately unravelling the fundamental processes in living systems. However, considering the different principles of each imaging method for probe design, it is still a great challenge to apply one molecular probe to achieve two or even more imaging analyses for biomarkers. In general, traditional oxime was reported as a recognition group for fluorescence imaging of HOCl. Herein, for the first time, we designed the oxime decorated iridium(III) complex, which can be directly used for chemiluminescence as well as two-photon luminescence and photoluminescence lifetime imaging of HOCl in living systems. Moreover, the novel chemiluminescence mechanism of Ir-CLFLPLIM for HOCl was also proposed and explored by continuously monitoring chemiluminescence peak shapes and mass spectra, inferring the reaction intermediate and calculating the chemical reaction energy range of the reaction process. This strategy could lead us to expand the chemiluminescence application of transition metal complexes and develop more multimodal imaging probes.

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.

Microfluidic Device for the Determination of Water Chlorination Levels Combining a Fluorescent meso-Enamine Boron Dipyrromethene Probe and a Microhydrocyclone for Gas Bubble Separation

Chlorination procedures are commonly applied in swimming pool water and wastewater treatment, yet also in food, pharmaceutical, and paper production. The amount of chlorine in water needs to be strictly controlled to ensure efficient killing of pathogens but avoid the induction of negative health effects. Miniaturized microfluidic fluorescence sensors are an appealing approach here when aiming at online or at-site measurements. Two meso-enamine-substituted boron dipyrromethene (BODIPY) dyes were found to exhibit favorable indication properties, their reaction with hypochlorite leading to strong fluorescence enhancement. Real-time assays became possible after integration of these fluorescent probes with designed two-dimensional (2D) and three-dimensional (3D) microfluidic chips, incorporating a passive sinusoidal mixer and a microhydrocyclone, respectively. A comparison of the two microfluidic systems, including their abilities to prevent accumulation or circulation of microbubbles produced by the chemical indication reaction, showed excellent fluidic behavior for the microhydrocyclone-based device. After coupling to a miniaturized optical reader for fluorescence detection, the 2D microfluidic system showed a promising detection range of 0.04-0.5 mg L^-1 while still being prone to bubble-induced fluctuations and suffering from considerably low signal gain. The microhydrocyclone-based system was distinctly more robust against gas bubbles, showed a higher signal gain, and allowed us to halve the limit of detection to 0.02 mg L^-1. The use of the 3D system to quantify the chlorine content of swimming pool water samples for sensitive and quantitative chlorine monitoring was demonstrated.

BODIPY-Derived Polymeric Chemosensor Appended with Thiosemicarbazone Units for the Simultaneous Detection and Separation of Hg(II) Ions in Pure Aqueous Media

Developing a simple and cheap analytical method for the selective detection and quantitative separation of toxic ions present in aqueous media is the biggest challenge faced by the chemosensing research community. Here, a 5,5-difluoro-1,3,7,9-tetramethyl-10-phenyl-5 H-dipyrrolo-diazaborinine-derived water-soluble polymer integrated with thiosemicarbazone units was rationally designed and synthesized for the simultaneous detection and separation of Hg(II) ions in pure aqueous solution. The water-soluble polymer scaffold poly( N, N'-dimethyl acrylamide- co-5,5-difluoro-1,3,7,9-tetramethyl-10-phenyl-5 H-dipyrrolo-diazaborinine-2-carbaldehyde) was synthesized by reversible addition-fragmentation chain transfer polymerization, followed by post-polymerization modification with thiosemicarbazide, leading to the formation of the target probe, P1. The nonemitting P1 exhibited bright yellow emission upon exposure to Hg(II) ions, with a limit of detection as low as 0.37 μM. This turn-on emission behavior triggered by Hg(II) ions might originate from the suppression of isomerization around the C═N bond of the thiosemicarbazone moiety caused by the formation of a coordination complex between P1 and Hg(II) ions. In addition, P1 displayed excellent selectivity toward Hg(II) ions over other metal cations. Finally, the selective removal of Hg(II) ions from an aqueous solution containing various metal ions was achieved by precipitation, which is probably caused by the fact that coordination complexes whereby Hg(II) ions acted as bridgeheads between P1 molecules had formed.

Ultrafast and Noninvasive Long-Term Bioimaging with Highly Stable Red Aggregation-Induced Emission Nanoparticles

Strongly red luminescent and water-soluble probes are very important for studying biological events and processes. Fluorescent nanoparticles (NPs) built from the aggregation-induced emission luminogen (AIEgen) and amphipathic polymeric matrixes have been considered as promising candidates for bioimaging. However, AIE NPs with long-wavelength absorption suitable for in vivo application are still scarce. In this work, three AIE-active red-emissive BODIPY derivatives with long-wavelength absorption were rationally designed and synthesized. Then three NPs based on these AIEgens exhibit bright red photoluminescence with high fluorescence quantum yield in aqueous media. These NPs uniformly dispersed in water and showed excellent stability and good biocompatibility. They can be readily internalized by HeLa cells, and the staining process is performed by simply shaking the culture with cells for just a few seconds at room temperature, which indicates an ultrafast and easy-to-operate staining protocol. More importantly, long-term tracing in living cells and mouse over 15 days is successfully achieved. The strong fluorescence signals, ultrafast staining procedure, and long-term tracing abilities indicate that these AIE NPs hold great potential for monitoring biological processes.

A "reactive" turn-on fluorescence probe for hypochlorous acid and its bioimaging application

An aza-BODIPY-CNOH probe attached aldoxime group demonstrated the specific detection for hypochlorous acid by the turn-on red emission signal. NMR and HRMS experiments confirmed that the fluorescence originated from the oxidation degradation of the non-fluorescence, aldoxime-based aza-BODIPY-CNOH probe into the red-fluorescence, nitrile oxide-based aza-BODIPY compound aza-BODIPY-CNO. The aza-BODIPY-CNOH probe showed good biocompatibility and was low toxic to living cells as shown from MTT experiments. Living RAW264.7 cells imaging indicated the aza-BODIPY-CNOH probe had good permeability and either exogenous or endogenous HClO caused the intracellular bright-red fluorescence, showing its potential hypochlorous acid-specific sensing ability in biological systems.

Detection of hypochlorous acid fluctuation via a selective near-infrared fluorescent probe in living cells and in vivo under hypoxic stress

The near-infrared fluorescent probe Cy-HOCl for monitoring HOCl in living cells, zebrafish and mice under hypoxic stress.

Photo-uncaging of BODIPY oxime ester for histone deacetylases induced apoptosis in tumor cells

A new photo-uncaging platform to guide drug delivery with enhanced therapeutic effect.

Overriding Phthalate Decomposition When Exploring Mycophenolic Acid Intermediates as Selenium-Based ROS Biological Probes

Hypochlorous (OCl^-) acid is the most well-known bacterial oxidant to be produced by neutrophils. Excess amounts of OCl^- can cause various disorders in living systems. Herein, we have designed, synthesized, and characterized two novel organoselenium-based target molecules (Probe-1 and Probe-OCl) based on a synthetic intermediate of mycophenolic acid for the aqueous detection of OCl^-. Probe 1 has been recently reported (Org. Lett. 2018, 20, 3557-3561); both probes show immediate "turn-on" fluorescence (<1 s) upon the addition of OCl^-, display an increase in the fluorescence quantum yield (3.7-fold in Probe-1 and 11.6-fold in Probe-OCl), and are completely soluble in aqueous media without the help of any cosolvent. However, a decrease in the "turn-on" intensity with the oxidized version of Probe-1 in cell assays due to the anhydride/phthalate functionality suggests that probe degradation occurs based on hydrolytic action (a probe degradation half-life of ∼1500 s at 15 μM Probe-1 and 150 μM OCl). Thus, the change of "anhydride" to "methylamide" begets Probe-OCl, which possesses more stability without sacrificing its water solubility properties and responses at short times. Further studies suggest that Probe-OCl is highly stable within physiological pH (pH = 7.4). Surprisingly, in live cell experiments involving U-2 OS cells and HeLa cells, Probe-OCl accumulated and aggregated in lipid droplets and gives a "turn-on" fluorescence response. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays confirmed that Probe-OCl is not toxic. Cuvette aggregation studies were also performed (tetrahydrofuran/H₂O) to demonstrate aggregation-induced fluorescence at longer times. Our current hypothesis is that the "turn-on" fluorescence effect is caused by the aggregation-induced emission mechanism available for Probe-OCl. In this case, in tandem, we reanalyzed the Mes-BOD-SePh derivative to compare and contrast cell localization as imaged by confocal microscopy; fluorescence emission occurs in the absence of, or prior to, Se oxidation.

Rapid Response Fluorescence Probe Enabled In Vivo Diagnosis and Assessing Treatment Response of Hypochlorous Acid-Mediated Rheumatoid Arthritis

Diagnosis and early assessment of the treatment response of rheumatoid arthritis (RA) necessitates a reliable bioanalytical method for rapid, sensitive, and specific detection of the hypochlorous acid (HOCl) biomarker in inflammatory diseases. Herein, two fluorescence probes, Probe-1 and Probe-2 are developed for quantitative monitoring and visualization of inflammatory response-related HOCl levels in vitro and in vivo. In the presence of HOCl, fluorescence "OFF-ON" response is obtained for both the probes as a result of specific HOCl-triggered C=N bond cleavage reaction. Probe-1 and Probe-2 feature rapid response (<4 s), a high degree of sensitivity and selectivity toward HOCl, which allow them to be used for quantification of HOCl in a simulated physiological condition. Using Probe-2 as the probe, fluorescence imaging and flow cytometry analysis of HOCl levels in lysosome of inflammatory mimic cells, visualization of HOCl generation in endotoxin-induced inflammation of adult zebrafish and RA of mice are possible. Probe-2 exhibits high effectiveness for early assessment of the treatment response of HOCl-mediated RA in mice with an antiarthritic drug, methotrexate (MTX). The results demonstrate that Probe-2 is a powerful tool for future studies on diagnosis and monitoring treatment efficiency in a broad range of inflammatory diseases, including RA.