Fluorescent Hydroxylamine Derived from the Fragmentation of PAMAM Dendrimers for Intracellular Hypochlorite Recognition

Herein, a promising sensing approach based on the structure fragmentation of poly(amidoamine) (PAMAM) dendrimers for the selective detection of intracellular hypochlorite (OCl^?) is reported. PAMAM dendrimers were easily disrupted by a cascade of oxidations in the tertiary amines of the dendritic core to produce an unsaturated hydroxylamine with blue fluorescence. Specially, the novel fluorophore was only sensitive to OCl^?, one of reactive oxygen species (ROS), resulting in an irreversible fluorescence turn‐off. The fluorescent hydroxylamine was selectively oxidised by OCl^? to form a labile oxoammonium cation that underwent further degradation. Without using any troublesomely synthetic steps, the novel sensing platform based on the fragmentation of PAMAM dendrimers, can be applied to detect OCl^? in macrophage cells. The results suggest that the sensing approach may be useful for the detection of intracellular OCl^? with minimal interference from biological matrixes.     

A Triphenyl Amine‐Based Solvatofluorochromic Dye for the Selective and Ratiometric Sensing of OCl− in Human Blood Cells

A new visible‐light‐excitable fluorescence ratiometric probe for OCl^? has been developed based on a triphenylamine‐diamiomaleonitrile (TAM) moiety. The structure of the dye was confirmed by single‐crystal X‐ray analysis. It behaves as a highly selective and sensitive probe for OCl^? over other analytes with a fast response time (～100 s). OCl^? reacts with the probe leading to the formation of the corresponding aldehyde in a mixed‐aqueous system. The detection limit of the probe is in the 10^?8 M range. The probe (TAM) also exhibits solvatofluorochromism. Changing the solvent from non‐polar to polar, the emission band of TAM largely red‐shifted. Moreover, the probe shows an excellent performance in real‐life application in detecting OCl^? in human blood cells. The experimentally observed changes in the structure and electronic properties of the probe after reaction with OCl^? were studied by DFT and TDDFT computational calculations.     

Novel triphenylamine-based fluorescent probe for specific detection and bioimaging of OCl−

Hypochlorite (OCl^?) plays important roles both in physiological and pathological processes, the detection of which is of great significance. Herein, a novel fluorescent probe based on the triphenylamine-type schiff base derivative (TPAD) was developed to detect OCl^?. Probe TPAD exhibited specific fluorescence response toward ClO^? with the fluorescence quenching rate up to 80%, and the detection limit was estimated to be 0.8?μM. The sensing mechanism study demonstrated that TPAD reacted with ClO^?via an oxidation process, which was evidenced by MS and NMR characterization. Moreover, owing to the excellent sensing properties and negligible cytotoxicity, TPAD was successfully applied in the bioimaging of OCl^? in living A549?cells.     

A mitochondria-targeted fluorescent probe for ratiometric detection of hypochlorite in living cells

A new fl uorescent probe 1 was designed for mitochondrial localization and ratiometric detection of hypochlorite in living cells. It is noteworthy that a high Pearson’s co-localization coeffi cient (Rr) we have obtained was calculated to be 0.97.     

A general strategy for selective detection of hypochlorous acid based on triazolopyridine formation

Triazolopyridines are an important kind of fused-ring compounds. A HOCl-promoted triazolopyridine formation strategy is reported here for the first time in which hypochlorous acid (HOCl) mildly and efficiently promotes the formation of 1,2,4-triazolo[4,3-a]pyridines NT1-NT6 from various 2-pyridylhydrazones N1-N6. N6, a rhodol-pyridylhydrazone hybrid, was developed into a fluorescent probe for the selective detection of HOCl, and successfully applied to probe endogenous HOCl in living cells and zebrafish in situ and in real time. The present intramolecular cyclization reaction is selective and atom-economical, thereby not only providing an important approach for the convenient synthesis of triazolopyridines, but also offering a general strategy for sensitive, selective and biocompatible detection of endogenous HOCl in complex biosystems.     

Development of Imidazoline‐2‐Thiones Based Two‐Photon Fluorescence Probes for Imaging Hypochlorite Generation in a Co‐Culture System

We designed and prepared the imidazoline‐2‐thione containing OCl^? probes, PIS and NIS , which operate through specific reactions with OCl^? that yield corresponding fluorescent imidazolium ions. Importantly, we demonstrated that PIS can be employed to image OCl^? generation in macrophages in a co‐culture system. We have also employed two‐photon microscopy and PIS to image OCl^? in live cells and tissues, indicating that this probe could have wide biological applications.     

Selective Detection and Visualization of Exogenous/endogenous Hypochlorous Acid in Living Cells using a BODIPY‐based Red‐emitting Fluorescent Probe

Herein, a red‐emitting fluorescent probe DM‐BDP‐OCl containing a para‐DMTC benzyl pyridinium moiety at the meso position of BODIPY as self‐immolative portion for the detection of HOCl was designed and synthesized. DM‐BDP‐OCl exhibited excellent specificity and a fast response for HOCl beyond other ROS/RNS. It was used for the accurately measurable detection of HOCl with a linear range from 0 μM to 50 μM, and the detection limit for HOCl reached 60 nM. Moreover, the probe could directly monitor fluctuations of exogenous and endogenous HOCl in living HeLa and RAW 264.7 cells. This work provided a powerful and convenient imaging tool for probing pathological and physiological actions of HOCl.     

A Reaction‐Based Fluorescent Probe for Imaging of Native Hypochlorous Acid

Hypochlorous acid (HOCl), one of the reactive oxygen species (ROS), is highly reactive and short‐lived. It is a challenge to dynamic monitor HOCl activity in living systems. Hence, we synthesized a new fluoresce nt probe RF1 based on protection of the hydroxyl group by N,N‐dimethylthiocarbamate recognition group, which reached a low fluorescence background signal and highly sensitive property. On account of the electrophilic addition of Cl⁺ to the sulfide of thiocarbamate moiety, probe RF1 was converted to resorufin and triggered emitting bright. RF1 showed not only the highly sensitive and selective response to HOCl in vitro, but also can be applied in environmental water samples and detected HOCl by test strips. Besides, the ability of RF1 monitoring HOCl in HeLa cells by exogenous simulation and tracing native HOCl in macrophages cells were also explored.     

Revealing HOCl burst from endoplasmic reticulum in cisplatin-treated cells via a ratiometric fluorescent probe

The reactive oxygen species (ROS) are tightly associated with endoplasmic reticulum (ER) stress. Thus, the deep and visual insight of aberrant ROS fluctuations in the ER can help us better investigate the ER stress-associated pathology. In this work, a fluorescent probe ERC for HOCl detection in the ER based on phenothiazine-derived coumarin platform was developed. In the presence of HOCl, ERC exhibited an emission change from 609 nm to 503 nm within seconds. It also showed high sensitivity (0.44 μmol/L) and superb photostability. Significantly, ERC displayed low cytotoxicity, good cell membrane permeability, and appreciable ER-targetability. Ultimately, the probe was successfully utilized to image exogenous and endogenous HOCl in living cells and reveal the HOCl burst in cisplatin-treated cancer cells.     

Hypochlorite‐Mediated Modulation of Photoinduced Electron Transfer in a Phenothiazine–Boron dipyrromethene Electron Donor–Acceptor Dyad: A Highly Water Soluble “Turn‐On” Fluorescent Probe for Hypochlorite

A highly water‐soluble phenothiazine (PTZ)–boron dipyrromethene (BODIPY)‐based electron donor–acceptor dyad ( WS‐Probe ), which contains BODIPY as the signaling antennae and PTZ as the OCl^? reactive group, was designed and used as a fluorescent chemosensor for the detection of OCl^?. Upon addition of incremental amounts of NaOCl, the quenched fluorescence of WS‐Probe was enhanced drastically, which indicated the inhibition of reductive photoinduced electron transfer (PET) from PTZ to ¹BODIPY*; the detection limit was calculated to be 26.7 nm . Selectivity studies with various reactive oxygen species, cations, and anions revealed that WS‐Probe was able to detect OCl^? selectively. Steady‐state fluorescence studies performed at varied pH suggested that WS‐Probe can detect NaOCl and exhibits maximum fluorescence in the pH range of 7 to 8, similar to physiological conditions. ESI‐MS analysis and ¹H NMR spectroscopy titrations showed the formation of sulfoxide as the major oxidized product upon addition of hypochlorite. More interestingly, when WS‐Probe was treated with real water samples, the fluorescence response was clearly visible with tap water and disinfectant, which indicated the presence of OCl^? in these samples. The in vitro cell viability assay performed with human embryonic kidney 293 (HEK 293) cells suggested that WS‐probe is non‐toxic up to 10 μm and implicates the use of the probe for biological applications.     

A Novel Phenoxazine-based Fluorescent Probe for the Detection of HOCl in Living Cells

Hypochlorous acid (HOCl), one of the reactive oxygen species (ROS), is a key microbicidal agent which is used for natural defense. However, it is also linked to varieties of human diseases owing to the overproduction of HOCl. Much effort has been made to exploit selective fluorescent sensors for the detection of HOCl, but most of them have some disadvantages such as short excitation wavelength, low selectivity, and slow response and so on. These restrict the biological application of the probes. In this work, BR-O was designed and synthesized on the base of phenoxazine for the detection of HOCl. BR-O exhibited a violent fluorescence enhancement in the presence of HOCl, showing excellent selectivity and high sensitivity. More importantly, the probe BR-O was capable of detecting exogenous and endogenous HOCl in living cells.     

Xanthene Dye Chemiluminescence for Determination of Free Chlorine in Water

Abstract

Preliminary investigations by a batch method are described for aiming at the flow determination of free chlorine in water with novel chemiluminescence (CL) detection. The CL originates from the reaction of xanthene dyes with free chlorine, Cl₂, HOCl, and OCl^?. Through the measurements of CL decay curves, fundamental CL characteristics were explored from the analytical point of view. Among xanthene dyes tested, eosin Y. eosin B. pyronin B. and rhodamine 6G were found to be promising CL reagents with such sensitivity and selectivity that free chlorine can be readily determined in tap water. In particular. these CL systems have the special advantage of being insensitive to oxo acids of chlorine and chloramine. Recommended flow systems are proposed.     

A pinacol boronate caged NIAD-4 derivative as a near-infrared fluorescent probe for fast and selective detection of hypochlorous acid

A pinacol boronate caged NIAD-4 derivative was demonstrated to be a near-infrared fluorescent probe for fast and selective detection of hypochlorite over other ROS species.     

Development of a BODIPY-based ratiometric fluorescent probe for hypochlorous acid and its application in living cells

A BODIPY-based ratiometric fluorescent probe for HOCl has been designed based on the transduction of thioether to sulfoxide function. This probe features a marked absorption and emission blue-shift upon the HOCl-promoted rapid transduction, enabling the highly selective and ratiometric detection. In addition, the probe works excellently within a wide pH range of 4–10, addressing the existing pH dependency issue. Living cells studies demonstrate that the probe is cell membrane permeable and can be employed successfully to image endogenous HOCl generation in macrophage cells.     

A general strategy for selective detection of hypochlorous acid based on triazolopyridine formation

Triazolopyridines are an important kind of fused-ring compounds. A HOCl-promoted triazolopyridine formation strategy is reported here for the first time in which hypochlorous acid (HOCl) mildly and efficiently promotes the formation of 1,2,4-triazolo[4,3-a]pyridines NT1-NT6 from various 2-pyridylhydrazones N1-N6. N6, a rhodol-pyridylhydrazone hybrid, was developed into a fluorescent probe for the selective detection of HOCl, and successfully applied to probe endogenous HOCl in living cells and zebrafish in situ and in real time. The present intramolecular cyclization reaction is selective and atom-economical, thereby not only providing an important approach for the convenient synthesis of triazolopyridines, but also offering a general strategy for sensitive, selective and biocompatible detection of endogenous HOCl in complex biosystems.     

Nanotechnology for Electroanalytical Biosensors of Reactive Oxygen and Nitrogen Species

Over the past several decades, nanotechnology has contributed to the progress of biomedicine, biomarker discovery, and the development of highly sensitive electroanalytical / electrochemical biosensors for in vitro and in vivo monitoring, and quantification of oxidative and nitrosative stress markers like reactive oxygen species (ROS) and reactive nitrogen species (RNS). A major source of ROS and RNS is oxidative stress in cells, which can cause many human diseases, including cancer. Therefore, the detection of local concentrations of ROS (e. g. superoxide anion radical; O₂^•−) and RNS (e. g. nitric oxide radical; NO^• and its metabolites) released from biological systems is increasingly important and needs a sophisticated detection strategy to monitor ROS and RNS in vitro and in vivo. In this review, we discuss the nanomaterials‐based ROS and RNS biosensors utilizing electrochemical techniques with emphasis on their biomedical applications.     

A Reversible Dual Mode Chemodosimeter for the Detection of Cyanide Ions in Natural Sources

Herein, we report the synthesis of two indolium probes 1 and 2 based on anthracene and pyrene derivatives and their interactions with various anions. Of these probes, the pyrene conjugate 2 acts as a dual colorimetric and fluorescent chemodosimeter for the selective and sensitive detection of cyanide ions. The detection limit of probe 2 for CN^? ions was found to be 10 ppb (30 nM ). The nature of interaction has been thoroughly studied through various techniques such as ¹H NMR and IR spectroscopy, HRMS, and isothermal calorimetric (ITC) studies. These studies confirm that probe 2 forms a 1,2‐adduct in the presence of CN^? ions. Kinetic studies using probe 2 showed the completion of the reaction within 15 s with a rate constant of k′=0.522±0.063 s^?1_. This probe can be coated on a solid surface (dipstick) and a polymer matrix for the on‐site analysis and quantification of endogenous cyanide ions in natural sources such as Indian almonds.     

A highly selective turn-on fluorescent probe for hypochlorous acid based on hypochlorous acid-induced oxidative intramolecular cyclization of boron dipyrromethene-hydrazone

A BODIPY-based fluorescent probe, HBP, was developed for the detection of hypochlorous acid based on the specific hypochlorous acid-promoted oxidative intramolecular cyclization of heterocyclic hydrazone in response to the amount of HOCl. The reaction is accompanied by a 41-fold increase in the fluorescent quantum yield (from 0.004 to 0.164). The fluorescence intensity of the reaction between HOCl and HBP is linear in the HOCl concentration range of 1–8 μM with a detection limit of 2.4 nM (S/N = 3). Confocal fluorescence microscopy imaging using RAW264.7 cells showed that the new probe HBP could be used as an effective fluorescent probe for detecting HOCl in living cells.     

Zn(ferulate)-LSH Systems as Multifunctional Filters

Excessive UV solar radiation exposure causes human health risks; therefore, the study of multifunctional filters is important to skin UV protective ability and also to other beneficial activities to the human organism, such as reduction of reactive oxygen species (ROS) responsible for cellular damages. Potential multifunctional filters were obtained by intercalating of ferulate anions into layered simple metal hydroxides (LSH) through anion exchange and precipitation at constant pH methods. Ultrasound treatment was used in order to investigate the structural changes in LSH-ferulate materials. Structural and spectroscopic analyses show the formation of layered materials composed by a mixture of LSH intercalated with ferulate anions, where carboxylate groups of ferulate species interact with LSH layers. UV-VIS absorption spectra and in vitro SPF measurements indicate that LSH-ferulate systems have UV shielding capacity, mainly UVB protection. The results of reactive species assays show the ability of layered compounds in capture DPPH^•, ABTS^•+, ROO^•, and HOCl/OCl⁻ reactive species. LSH-ferulate materials exhibit antioxidant activity and singular optical properties that enable their use as multifunctional filters.     

Turn‐On Luminescent Probes for the Real‐Time Monitoring of Endogenous Hydroxyl Radicals in Living Cells

The utilization of semiconductor quantum dots (QDs) as optical labels for biosensing and biorecognition has made substantial progress. However, the development of a suitable QD‐based luminescent probe that is capable of detecting individual reactive oxygen species (ROS) represents a great challenge, mainly because the fluorescence of QDs is quenched by a wide variety of ROS. To overcome this limitation, a novel QD‐based turn‐on luminescent probe for the specific detection of ^.OH has been designed, and its application in monitoring the endogenous release of ^.OH species in living cells is demonstrated. Metal citrate complexes on the surfaces of the QDs can act as electron donors, injecting electrons into the LUMO of the QDs, while ^.OH can inject holes into the HOMO of the QDs. Accordingly, electron–hole pairs are produced, which could emit strong luminescence by electron–hole recombination. Importantly, this luminescent probe does not respond to other ROS.