Ratiometric Fluorescent Probes for Detection of Intracellular Singlet Oxygen

On-Site Quantitative Visualization of Singlet Oxygen in Crops via an Organic Small Molecule-Based Ratiometric Fluorescent Probe and a Mobile Fluorescence Analysis Device

Singlet oxygen (1O2) plays imperative roles in a variety of biotic or abiotic stresses in crops. The change of its concentration within a crop is closely related to the crop growth and development. Accordingly, there is an urgent need to develop an efficient analytical method for on-site quantitative detection of 1O2 in crops. Here, we judiciously constructed a novel ratiometric fluorescent probe, SX-2, for the detection of 1O2 in crops. Upon treating with 1O2, probe SX-2 displayed highly selective ratiometric fluorescence response, which is favorable for the quantitative detection of 1O2. Concurrently, the fluorescence solution color of probe SX-2 was varied, obviously from blue to yellow, indicating that the probe is beneficial for on-site detection by the naked eye. Sensing reaction mechanism studies showed that the 2,3-diphenyl imidazole group in SX-2 could function as a new selective recognition group for 1O2. Probe SX-2 was utilized for the detection of photoirradiation-induced 1O2 and endogenous 1O2 in living cells. The changes in the 1O2 level in zebrafish were also tracked by fluorescence imaging. In addition, the production of 1O2 in crop leaves under a light source of different wavelengths was studied. The results demonstrated more 1O2 were produced under a light source of 365 nm. Furthermore, to achieve on-site quantitative detection, a mobile fluorescence analysis device has been made. Probe SX-2 and mobile fluorescence analysis device were capable of on-site quantitative detecting of 1O2 in crops. The method developed herein will be convenient for the on-site quantitative measurement of 1O2 in distinct crops.

A comprehensive review on singlet oxygen generation in nanomaterials and conjugated polymers for photodynamic therapy in the treatment of cancer

A key role in lessening humanity's continuous fight against cancer could be played by photodynamic therapy (PDT), a minimally invasive treatment employed in the medical care of a range of benign disorders and malignancies. Cancerous tissue can be effectively removed by using a light source-excited photosensitizer. Singlet oxygen and reactive oxygen species are produced via the photosensitizer as a result of this excitation. In the recent past, researchers have put in tremendous efforts towards developing photosensitizer molecules for photodynamic treatment (PDT) to treat cancer. Conjugated polymers, characterized by their efficient fluorescence, exceptional photostability, and strong light absorption, are currently under scrutiny for their potential applications in cancer detection and treatment through photodynamic and photothermal therapy. Researchers are exploring the versatility of these polymers, utilizing sophisticated chemical synthesis and adaptable polymer structures to create new variants with enhanced capabilities for generating singlet oxygen in photodynamic treatment (PDT). The incorporation of photosensitizers into conjugated polymer nanoparticles has proved to be beneficial, as it improves singlet oxygen formation through effective energy transfer. The evolution of nanotechnology has emerged as an alternative avenue for enhancing the performance of current photosensitizers and overcoming significant challenges in cancer PDT. Various materials, including biocompatible metals, polymers, carbon, silicon, and semiconductor-based nanomaterials, have undergone thorough investigation as potential photosensitizers for cancer PDT. This paper outlines the recent advances in singlet oxygen generation by investigators using an array of materials, including graphene quantum dots (GQDs), gold nanoparticles (Au NPs), silver nanoparticles (Ag NPs), titanium dioxide (TiO2), ytterbium (Yb) and thulium (Tm) co-doped upconversion nanoparticle cores (Yb/Tm-co-doped UCNP cores), bismuth oxychloride nanoplates and nanosheets (BiOCl nanoplates and nanosheets), and others. It also stresses the synthesis and application of systems such as amphiphilic block copolymer functionalized with folic acid (FA), polyethylene glycol (PEG), poly(β-benzyl-L-aspartate) (PBLA10) (FA-PEG-PBLA10) functionalized with folic acid, tetra(4-hydroxyphenyl)porphyrin (THPP-(PNIPAM-b-PMAGA)4), pyrazoline-fused axial silicon phthalocyanine (HY-SiPc), phthalocyanines (HY-ZnPcp, HY-ZnPcnp, and HY-SiPc), silver nanoparticles coated with polyaniline (Ag@PANI), doxorubicin (DOX) and infrared (IR)-responsive poly(2-ethyl-2-oxazoline) (PEtOx) (DOX/PEtOx-IR NPs), particularly in NIR imaging-guided photodynamic therapy (fluorescent and photoacoustic). The study puts forward a comprehensive summary and a convincing justification for the usage of the above-mentioned materials in cancer PDT.

Reactive oxygen species in biological media are they friend or foe? Major In vivo and In vitro sensing challenges

The role of Reactive Oxygen Species (ROS) on biological media has been shifting over the years, as the knowledge on the complex mechanism that lies in underneath their production and overall results has been growing. It has been known for some time that these species are associated with a number of health conditions. However, they also participate in the immunoactivation cascade process, and can have an active role in theranostics. Macrophages, for example, react to the presence of pathogens through ROS production, potentially allowing the development of new therapeutic strategies. However, their short lifetime and limited spatial distribution of ROS have been limiting factors to the development and understanding of this phenomenon. Even though, ROS have shown successful theranostic applications, e.g., photodynamic therapy, their wide applicability has been hampered by the lack of effective tools for monitoring these processes in real time. Thus the development of innovative sensing strategies for in vivo monitoring of the balance between ROS concentration and the resultant immune response is of the utmost relevance. Such knowledge could lead to major breakthroughs towards the development of more effective treatments for neurodegenerative diseases. Within this review we will present the current understanding on the interaction mechanisms of ROS with biological systems and their overall effect. Additionally, the most promising sensing tools developed so far, for both in vivo and in vitro tracking will be presented along with their main limitations and advantages. This review focuses on the four main ROS that have been studied these are: singlet oxygen species, hydrogen peroxide, hydroxyl radical and superoxide anion.

A novel antibacterial and fluorescent coating composed of polydopamine and carbon dots on the surface of orthodontic brackets

Many kinds of antibacterial coatings have been designed to prevent the adherence of bacteria onto the surface of a fixed orthodontic device of brackets. However, the problems such as weak binding force, undetectable, drug resistance, cytotoxicity and short duration needed to be solved. Thus, it has great value in developing novel coating methods with long-term antibacterial and fluorescence properties according to the clinical application of brackets. In this study, we synthesized blue fluorescent carbon dots (HCDs) using the traditional Chinese medicinal honokiol, which could cause irreversible killing effects on both gram-positive and gram-negative bacteria through positive charges on the surface and inducing reactive oxygen species (ROS) production. Based on this, the surface of brackets was serially modified with polydopamine and HCDs, taking advantage of the strong adhesive properties as well as the negative surface charge of polydopamine particles. It is found that this coating exhibits stable antibacterial properties in 14 days with good biocompatibility, which can provide a new solution and strategy to solve the series of hazards caused by bacterial adhesion on the surface of orthodontic brackets.

Biocompatible Fluorescent Biosensor Reveals the Level and Distribution of Indole-3-Acetic Acid Signals in Plants

To fully understand the function of the phytohormone indole-3-acetic acid (IAA) in regulating plant growth and development, we need to monitor their levels and distribution with high spatial and temporal resolution. In this work, an anthracene-based fluorescent biosensor for IAA was prepared using bovine serum albumin (BSA) as a bio-template. The single linear oxygen (¹O₂) specifically produced by IAA catalyzed with horseradish peroxidase (HRP) turns on the fluorescence of the probe, enabling specific trace sensing of IAA in the presence of multiple structural analogues. The presence of the bio-template BSA extends the biocompatibility of the probe, enabling visual monitoring of the level and distribution signal of endogenous IAA of plants in the field of bioimaging. In addition, the strategy has shown potential for application in portable paper-based sensors and in vivo fluorescent flower culture. This work provides a technical and theoretical basis for exploring the growth regulatory mechanisms of IAA in plants at the molecular level.

Ratiometric Singlet Oxygen Sensor Based on BODIPY-DPA Dyad

Compounds sensitive to reactive oxygen species are widely used in the study of processes in living cells and in the development of therapeutic agents for photodynamic therapy. In the present work, we have synthesized a dyad in which the BODIPY dye is chemically bound to 9,10-diphenylanthracene (DPA). Here, DPA acts as a specific sensor of singlet oxygen and BODIPY as a reference dye. We studied the photophysical properties of the BODIPY-DPA dyad and showed that energy transfer occurs between the chromophores. As a result, the compound has excitation maxima in the absorption region of both DPA and BODIPY, but the fluorescence emission occurs mainly from BODIPY. In the presence of singlet oxygen, the excitation maximum of DPA decreases, while the intensity of the excitation maximum of BODIPY remains almost unchanged. This allows the BODIPY-DPA dyad to be used as a ratiometric sensor of singlet oxygen.

Effect of Activation Methods of Molecular Sieves on Ketimine Synthesis

Although the use of molecular sieves for imine synthesis is a common protocol, there have been no comprehensive studies on heat-drying methods. This can be crucial for reproducibility. It was found that molecular sieve 5A dried at 160 °C for 5 h under vacuum efficiently promoted the condensation of various ketones and amines to afford even relatively bulky ketimines. Several control experiments and analyses revealed that only a small amount of Brønsted acid sites was important for the activity, rather than dehydration ability. Other types of molecular sieves could be utilized for the reaction after treatment with water followed by heat drying. A continuous-flow acetalization reaction of alcohols using the activated molecular sieve 5A was also demonstrated.

Red to NIR-emissive anthracene-conjugated PMI dyes with dual functions: singlet-oxygen response and lipid-droplet imaging

The rich chemistry of solution-processable red and near-infrared (NIR) organic emitters has emerged as an attractive and progressive research field because of their particular applications in organic optoelectronics and bioimaging. Also, one can see that the research area of perylene monoimide-based red and NIR-emissive fluorophores is underexplored, which prompted us to design and synthesize three anthracene-conjugated PMI dyes exhibiting strong emission in the red and NIR window in solution. Three PMI-based fluorophores were synthesized via conjoining anthracene and donor moieties (-Ph, -N,N-PhNMe₂) with a PMI core via an acetylene linkage at the peri-position, which helped to attain extensive electronic conjugation, which was reflected in red and NIR-emission in solution. The key molecular features to be highlighted here are: all three dyes are strongly emissive in solution, as unveiled by the excellent absolute fluorescence QYs; and they possess tuneable emission properties, guided by the donor strength and a profound Stokes shift (100-200 nm). The three fluorescent dyes demonstrated appreciable singlet-oxygen (¹O₂) sensitivity when photoirradiated with methylene blue (MB) in solution, showing a substantial blue-shift in emission in a ratiometric manner. Further, the treatment of dye-MB solution with α-tocopherol (¹O₂ scavenger) validated the presence of ¹O₂ as the only oxidizing species generated by MB in solution. Computational investigations gave insight into the twisting of donor moieties in their ground-state optimized geometries, the modulation of the FMO energy gap, and the thermodynamic feasibility of the ¹O₂ reaction. Finally, via taking advantage of the red and NIR-emission, we successfully utilized one of the fluorophores as a lipid-droplet marker for bioimaging in HepG2 cells.

A two-photon fluorescence probe with endoplasmic reticulum targeting ability for turn-on sensing photosensitized singlet oxygen in living cells and brain tissues

Endoplasmic reticulum (ER) is an indispensable organelle responsible for protein synthesis, transportation, and maintenance of Ca²⁺ homeostasis in eukaryotic cells. Recent studies highlighted that ER-targeted photosensitizers with high yield of singlet oxygen (¹O₂) are effective in selectively disrupting ER function and are promising candidates for anticancer therapy. Unfortunately, no ER targetable fluorescent probes for determining ¹O₂ photosensitized in this photodynamic therapy process is available. In this work, we synthesized an ER-targetable, two-photon fluorescence probe, ER-¹O₂, for fluorescence turn-on sensing of ¹O₂. ER-¹O₂ demonstrated high sensitivity to ¹O₂ sensing with a wide detection range (0-2.75 μM) and a low detection limit (0.11 μM). ER-¹O₂ also displayed excellent selectivity toward ¹O₂ out of other ROS and metal ions. Notably, ER-¹O₂ exhibited low cytotoxicity but with specific ER targetable capability. On account of these advantageous features, fluctuations of ¹O₂ in living cells and brain tissues were effectively visualized by ER-¹O₂.

Optical/electrochemical methods for detecting mitochondrial energy metabolism

This review highlights the biological importance of mitochondrial energy metabolism and the applications of multiple optical/electrochemical approaches to determine energy metabolites. Mitochondria, the main sites of oxidative phosphorylation and adenosine triphosphate (ATP) biosynthesis, provide the majority of energy required by aerobic cells for maintaining their physiological activity. They also participate in cell growth, differentiation, information transmission, and apoptosis. Multiple mitochondrial diseases, caused by internal or external factors, including oxidative stress, intense fluctuations of the ionic concentration, abnormal oxidative phosphorylation, changes in electron transport chain complex enzymes and mutations in mitochondrial DNA, can occur during mitochondrial energy metabolism. Therefore, developing accurate, sensitive, and specific methods for the in vivo and in vitro detection of mitochondrial energy metabolites is of great importance. In this review, we summarise the mitochondrial structure, functions, and crucial energy metabolic signalling pathways. The mechanism and applications of different optical/electrochemical methods are thoroughly reviewed. Finally, future research directions and challenges are proposed.

Red-Emitting, Acene-Doped Conjugated Polymer Nanoparticles that Respond Ratiometrically to Photogenerated 1O2

Fluorophores that respond to external stimuli on demand have numerous applications in imaging and chemical or biological sensing. In this paper, we describe conjugated polymer nanoparticles (CPNs) that comprise a donor polymer matrix and a red-fluorescent, singlet oxygen-reactive heteroacene dopant (DE-TMT) that display a ratiometric response upon photo-oxidation. This ratiometric response can be tuned by the level of doping of DE-TMT, the identity of the conjugated polymer matrix used, and the blending of two conjugated polymers together to access red-shifted emission wavelengths. We followed a rational design process that combined (i) fundamental understanding of the influence of the chemical structure on luminescence spectra and efficiencies, energy transfer efficiencies, and reactivity and (ii) systematically determining how blending multiple chromophores in nanoparticles influences energy transfer efficiencies and the speed of optical responses to irradiation. Our approach of refining the compositions of these nanoparticles has yielded materials that combine many desirable characteristics for analytical applications-utility in aqueous environments, high quantum yield, emission of red light, and ratiometric luminescent responses. We anticipate that the type of approach described herein can be of use to others in designing CPNs for luminescence applications.

Detection of lipase activity in human serum based on a ratiometric fluorescent probe

CARA can monitor lipase activity through hydrolyzing the ester bond to interrupt the FRET process.

Resistance to Unwanted Photo-Oxidation of Multi-Acene Molecules

Although long acenes remain a key class of π-conjugated molecules for numerous applications, photoinduced oxidation upon exposure of the acene to light, often through sensitization of ¹O₂, is an important reaction requiring mitigation for most applications. In response to this ongoing challenge, this paper presents a series of four new diarylethynyl-substituted long acenes-three tetracenes and one anthradithiophene-in which the arylene pendants are either benzene, naphthalene, or anthracene. UV/vis and fluorescence spectroscopy reveals that the anthracene-substituted derivatives fluoresce poorly (Φ < 0.01). Although all four long acenes react with ¹O₂ at expected rates when an external photosensitizer is included and show the expected changes in fluorescence to accompany these reactions, the anthracene-substituted derivatives resist direct photoinduced oxidation. Through a combination of mechanistic experiments, we conclude that rapid nonradiative decay of the anthracene-substituted derivatives, perhaps because of inter-arene torsions that emerge in theoretical geometry optimizations, makes these compounds poor photosensitizers for ¹O₂ or other reactive oxygen species. This discovery opens new design possibilities for extended acene structures with improved photochemical stability.

Quantitative kinetics of intracellular singlet oxygen generation using a fluorescence probe

Singlet oxygen (¹O₂) is a type of reactive oxygen species involved in numerous physiological activities. We previously reported that ¹O₂-specific oxidation products are increased in patients with prediabetes, suggesting that measurement of ¹O₂ may be an important indicator of physiological and pathological conditions. The turnover in the generation and quenching of ¹O₂ is extremely rapid during biological activities owing to it high reactivity and short lifetime in solution. However, the dynamic changes in ¹O₂ generation in living cells have not been fully explored. In this study, we investigated whether the kinetics of ¹O₂ generation can be quantified using a far-red fluorescent probe for mitochondrial ¹O₂, Si-DMA, following addition of the ¹O₂ generator, endoperoxide, to mammalian cells. The kinetics of Si-DMA fluorescence intensity dose-dependently increased following treatment of mammalian living cells with endoperoxide. Alternatively, treatment with ¹O₂ quenchers decreased the fluorescence intensities following endoperoxide treatment. Our results indicate that the kinetics of intracellular ¹O₂ can be readily obtained using Si-DMA and time-lapse imaging, which provides new insights into the mechanism of ¹O₂ generation in mammalian cells and the exploration of ¹O₂ generators and quenchers.

Carbon dot-assisted luminescence of singlet oxygen: the generation dynamics but not the cumulative amount of singlet oxygen is responsible for the photodynamic therapy efficacy

A novel carbon dot-based luminescence probe for singlet oxygen (¹O₂) with a conventional optical detector has been implemented through the specific formation of electronically excited carbonyls from the breakdown of unstable endoperoxide intermediates, and its application in the real-time in vivo monitoring of ¹O₂ in photodynamic therapy (PDT) is achieved. More attractively, the relationship between the dynamics details of photosensitizer-generated ¹O₂ and the PDT efficacy has been established through a modified multiple-target survival model, enabling a direct and easy estimate of the surviving fraction of tumor cells from the generation dynamics of ¹O₂. Both in vitro and in vivo therapy results revealed that the rapid generation dynamics of ¹O₂ rather than its cumulative amount is responsible for better treatment efficacy in PDT. Overall, the deeper insight into the important roles of the generation dynamics of ¹O₂ in the PDT efficacy is irreplaceably advantageous in substantially reduced risks from deleterious treatment-related side effects by screening advanced photosensitizers and determining the light exposure end point.

Revealing the Photodynamic Stress In Situ with a Dual-Mode Two-Photon 1O2 Fluorescent Probe

Singlet oxygen (¹O₂) plays significant physiological and pathological functions, especially in causing photodynamic stress in vivo. However, specific ¹O₂ monitoring is an immense challenge, owing to its short half-lives and high oxidizing ability. To address this, we engineered three photostable two-photon fluorescence probe NBs for highly efficient ¹O₂ monitoring based on bioinspired novel tryptophan derivatives, among which NB-MOT was the best one comprehensively. Upon being cracked with ¹O₂, NB-MOT rapidly (within 5 s) demonstrated a remarkable enhancement in fluorescence intensity (∼180 fold) and lifetime (∼18 fold). Taking these advantages into account, NB-MOT was applied to evaluate exogenous and endogenous ¹O₂ in diverse biosystems. We successfully tracked the intracellular ¹O₂ level during photodynamic therapy, and for the first time achieved ¹O₂ mapping in live cells with dual-mode imaging as well as revealed ciprofloxacin-induced photodynamic stress in mice. NB-MOT was thus believed to be of instructive significance for studying the ¹O₂-mediated stress in wider biological milieus.

BF3-Etherate-catalyzed tandem reaction of 2-formylarylketones with electron-rich arenes/heteroarenes: an assembly of isobenzofurans

An efficient and BF₃·Et₂O-catalyzed chemoselective synthesis of diversified 1,3-diarylisobenzofuran in a high yield has been described.

Acenes beyond organic electronics: sensing of singlet oxygen and stimuli-responsive materials

Although they are often detrimental in organic electronics, the cycloaddition reactions of acenes, especially with singlet oxygen, are useful in a range of responsive materials.

Development of a Fluorescent Probe for Measurement of Singlet Oxygen Scavenging Activity of Flavonoids

A turn-on fluorescent probe, HOCD-RB, for monitoring singlet oxygen (¹O₂) was developed by linking rhodamine B as fluorophore with dimethylhomoocoerdianthrone (HOCD) as ¹O₂ reaction site and fluorescence quencher due to the intramolecular energy transfer (ET) between rhodamine B and HOCD moieties. Upon exposure to ¹O₂ it rapidly forms endoperoxide with HOCD and turns on the fluorescence of rhodamine B by 18-fold. Taking advantage of the HOCD-RB probe that shows fast response, high sensitivity, and selectivity for ¹O₂, it is applied for imaging of endogenous ¹O₂ in living cells and the fluorometric assay for evaluating ¹O₂ quenching activity of selected common flavonoids found in our daily diets. The results show that the ¹O₂ scavenging activity of flavonoids depends on not only the structure of individual flavonoid but also the competitive interactions between mixed flavonoids. The best antioxidant capacity for individual and mixed flavonoids is epigallocatechin gallate and the mixture of catechin gallate with kaempferol, respectively. Overall, this work provided a new tool for detection and imaging of singlet oxygen activity in a biological system as well as an efficient fluorometric assay of ¹O₂ scavenging activity.

Construction of a fluorescent probe for selectively detecting singlet oxygen with a high sensitivity and large concentration range based on a two-step cascade sensing reaction

A novel fluorescent probe XQ-1 for selectively detecting ¹O₂ on the basis of a two-step cascade reaction has been rationally constructed. The probe responded to ¹O₂ not only showing a high sensitivity, but also displaying a large concentration range, which means that the probe can be used as a powerful tool to monitor the efficacy of PDT toward cancer and concurrently track the adverse effects on healthy cells.

Real-Time Mapping of Ultratrace Singlet Oxygen in Rat during Acute and Chronic Inflammations via a Chemiluminescent Nanosensor

Sensing nonradiation-induced singlet oxygen (¹ O₂ ) in whole-animal is deemed as one of the most challenging tasks in noninvasive techniques due to the µs level lifetime of ¹ O₂ and quenching by numerous reductants in tissues. Here a distinct chemiluminescent (CL) nanosensor (NTPE-PH) that boasts ultrahigh concentrated CL units in one nanoparticle is reported. Taking advantage of the intramolecular energy transfer mechanism that promises high energy transfer efficiency and the aggregation-induced emission behavior that guarantees high CL amplification, the NTPE-PH sensor is sensitive to a nm level ¹ O₂ . Experiments demonstrate that the NTPE-PH yields a highly selective CL response toward ¹ O₂ among common reactive oxygen species. With proved low cytotoxicity and good animal compatibility, real-time mapping of ultratrace ¹ O₂ in whole-animal during acute and chronic inflammations is first achieved. It is anticipated that the NTPE-PH sensor can be a useful tool for monitoring ¹ O₂ variation during immune response and pathological processes corresponding to different stimuli, even with drug treatment included.

Chemical tools for the generation and detection of singlet oxygen

Growing evidence indicates intermediacy of singlet dioxygen (1O2) in a variety of pathophysiological processes. 1O2 has also found great utility of destructive actions for clinical and environmental applications. However, many details of the molecular mechanisms mediated by 1O2 remain insufficiently understood. Efforts to elucidate the 1O2 chemistry have been hampered by the lack of chemical tools capable of generation and detection of 1O2. In this review, I summarize the recent advances in the development of the chemical tools of 1O2. This article focuses on two topics. The first part introduces chemical methods for ground-state generation of 1O2. Designs of the molecular carriers of 1O2 are also explained. The second part discloses molecular probes of 1O2. The probes are categorized into three groups, depending on signaling modalities: absorption-based probes, photoluminescent probes, and chemiluminescent probes. Focus is on the molecular design to maximize the signaling actions. Disadvantages of using the probes are also discussed to motivate the future research. I hope that this review will serve as helpful guidance to the exploitation and development of the chemical tools of 1O2.

A coumarin chalcone ratiometric fluorescent probe for hydrazine based on deprotection, addition and subsequent cyclization mechanism

A coumarin chalcone derivative with a levulinic acid terminal group acts as a ratiometric fluorescent probe for hydrazine based on deprotection, addition and a subsequent cyclization reaction mechanism.

Structure-activity study of furyl aryloxazole fluorescent probes for the detection of singlet oxygen

In this study, we report the synthesis and the photochemical behavior of a series of new "click-on" fluorescent probes designed to detect singlet oxygen. They include a highly fluorescent chemical structure, an aryloxazole ring, linked to a furan moiety operating as singlet oxygen trap. Their activity depends on both the structure of the aryloxazole fluorophore and the electron-donating and electron-accepting properties of the substituents attached to the C-5 of the furan ring. All probes are selectively oxidized by singlet oxygen to give a single fluorescent product in methanol and produce negligible amounts of singlet oxygen themselves by self-sensitization. The most promising dyad, (E)-2-(2-(5-methylfuran-2-yl)vinyl)naphtho[1,2-d]oxazole, FN-6, shows outstanding reactivity and sensitivity: it traps singlet oxygen with a rate constant (5,8 ± 0.1) x 1(07) M-1 s-1 and its fluorescence increases by a factor of 500 upon reaction. Analysis of the dyads reactivity in terms of linear free energy relationships using the modified Swain and Lupton parameter F and the Fukui condensed function for the electrophilic attack, suggests that cycloaddition of singlet oxygen to the furan ring is partially concerted and possibly involves an exciplex with a "more open" structure than could be expected for a concerted cycloaddition.

A fluorescent nanoprobe for real-time monitoring of intracellular singlet oxygen during photodynamic therapy

Sensing of intracellular singlet oxygen (¹O₂) is required in order to optimize photodynamic therapy (PDT). An optical nanoprobe is reported here for the optical determination of intracellular ¹O₂. The probe consists of a porous particle core doped with the commercial ¹O₂ probe 1,3-diphenylisobenzofuran (DPBF) and a layer of poly-L-lysine. The nanoparticle probes have a particle size of ~80 nm in diameter, exhibit good biocompatibility, improved photostability and high sensitivity for ¹O₂ in both absorbance (peak at 420 nm) and fluorescence (with excitation/emission peaks at 405/458 nm). Nanoprobes doped with 20% of DPBF are best suited even though they suffer from concentration quenching of fluorescence. In comparison with the commercial fluorescent ¹O₂ probe SOSG, 20%-doped DPBF-NPs (aged) shows higher sensitivity for ¹O₂ generated at an early stage. The best nanoprobes were used to real-time monitor the PDT-triggered generation of ¹O₂ inside live cells, and the generation rate is found to depend on the supply of intracellular oxygen. Graphical abstract A fluorescent nanoprobe featured with refined selectivity and improved sensitivity towards ¹O₂ was prepared from the absorption-based probe DBPF and used to real-time monitoring of the generation of intracellular ¹O₂ produced during PDT.

An efficient two-photon fluorescent probe for monitoring mitochondrial singlet oxygen in tissues during photodynamic therapy

A promising two-photon fluorescent probe MNAH for detecting ¹O₂ during the PDT process in mitochondria was proposed for the first time. MNAH was successfully applied for two-photon imaging of ¹O₂ in living cells and tissues during the PDT process with deep-tissue imaging depth. MNAH can be a powerful molecular tool for studying ¹O₂ generation in mitochondria during the PDT process.

Distinct ON/OFF fluorescence signals from dual-responsive activatable nanoprobes allows detection of inflammation with improved contrast

Visualization of biochemical changes associated with disease is of great clinical significance, as it should allow earlier, more accurate diagnosis than structural imaging, facilitating timely clinical intervention. Herein, we report combining stimuli-responsive polymers and near-infrared fluorescent dyes (emission max: 790 nm) to create robust activatable fluorescent nanoprobes capable of simultaneously detecting acidosis and oxidative stress associated with inflammatory microenvironments. The spectrally-resolved mechanism of fluorescence activation allows removal of unwanted background signal (up to 20-fold reduction) and isolation of a pure activated signal, which enables sensitive and unambiguous localization of inflamed areas; target-to-background ratios reach 22 as early as 3 h post-injection. This new detection platform could have significant clinical impact in early detection of pathologies, individual tailoring of drug therapy, and image-guided tumor resection.

Ratiometric Singlet Oxygen Detection in Water Using Acene-Doped Conjugated Polymer Nanoparticles

Although fluorescent probes for the detection of singlet oxygen (1O2) have been an active area of research, most such probes rely upon change in intensity of a single band. Herein, we report a FRET-based, 1O2-sensitive aqueous suspension of conjugated polymer nanoparticles (CPNs) comprising the energy-donating host polymer poly[{9,9-dioctyl-2,7-divinylene-fluorenylene}-alt-co-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene}] doped with an energy acceptor, the 1O2-sensitive thienoacene 5,12-bis(4-methoxyphenyl)-2-butyltetraceno[2,3-b]thiophene. Using a phthalocyanine-based sensitizer, IRDye 700DX, our probe shows a rapid, ratiometric response to photosensitized 1O2 in water in both cuvettes and 96-well plates that compares favorably to the commercial 1O2-sensitive dye, singlet oxygen sensor green. The response to irradiation of even nanomolar concentrations of photosensitizer demonstrates the sensitivity of our ratiometric probe.

Dual-emissive polystyrene@zeolitic imidazolate framework-8 composite for ratiometric detection of singlet oxygen

The co-encapsulation of EuPS and AnC in a ZIF-8 host leads to the formation of a dual-emissive composite for fluorescent ratiometric sensing of singlet oxygen.

Oxidative stress in oral diseases

Oxidative species, including reactive oxygen species (ROS), are components of normal cellular metabolism and are required for intracellular processes as varied as proliferation, signal transduction, and apoptosis. In the situation of chronic oxidative stress, however, ROS contribute to various pathophysiologies and are involved in multiple stages of carcinogenesis. In head and neck cancers specifically, many common risk factors contribute to carcinogenesis via ROS-based mechanisms, including tobacco, areca quid, alcohol, and viruses. Given their widespread influence on the process of carcinogenesis, ROS and their related pathways are attractive targets for intervention. The effects of radiation therapy, a central component of treatment for nearly all head and neck cancers, can also be altered via interfering with oxidative pathways. These pathways are also relevant to the development of many benign oral diseases. In this review, we outline how ROS contribute to pathophysiology with a focus toward head and neck cancers and benign oral diseases, describing potential targets and pathways for intervention that exploit the role of oxidative species in these pathologic processes.

A singlet oxygen photosensitizer enables photoluminescent monitoring of singlet oxygen doses

Dichromophoric molecular dyad enables photosensitization and detection of sinlget oxygen.

High-resolution in vivo optical imaging of stroke injury and repair

Central nervous system (CNS) function and dysfunction are best understood within a framework of interactions between neuronal, glial and vascular compartments comprising the neurovascular unit (NVU), all of which contribute to stroke-induced CNS injury, plasticity, repair, and recovery. Recent advances in in vivo optical microscopy have enabled us to observe and interrogate cells and their processes with high spatial resolution in real time and in their natural environment deep in the brain tissue. Here, we review some of these state-of-the-art imaging techniques with an emphasis on imaging the interactions among the constituents of the NVU during ischemic injury and repair in small animal models. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Protein-encapsulated bilirubin: paving the way to a useful probe for singlet oxygen

Oxygen- and singlet-oxygen-dependent parameters that characterize the behavior of bilirubin encapsulated in a protein have been quantified.

Far-red fluorescence probe for monitoring singlet oxygen during photodynamic therapy

Singlet oxygen ((1)O2), molecular oxygen in the lowest excited state, has a critical role in the cell-killing mechanism of photodynamic therapy (PDT). Although (1)O2 phosphorescence measurement has been mainly used to monitor (1)O2 formation during PDT, its intensity is far insufficient to obtain two-dimensional images of intracellular (1)O2 with the subcellular spatial resolution using the currently available near-IR detector. Here, we propose a new far-red fluorescence probe of (1)O2, namely, Si-DMA, composed of silicon-containing rhodamine and anthracene moieties as a chromophore and a (1)O2 reactive site, respectively. In the presence of (1)O2, fluorescence of Si-DMA increases 17 times due to endoperoxide formation at the anthracene moiety. With the advantage of negligible self-oxidation by photoirradiation (ΦΔ < 0.02) and selective mitochondrial localization, Si-DMA is particularly suitable for imaging (1)O2 during PDT. Among three different intracellular photosensitizers (Sens), Si-DMA could selectively detect the (1)O2 that is generated by 5-aminolevulinic acid-derived protoporphyrin IX, colocalized with Si-DMA in mitochondria. On the other hand, mitochondria-targeted KillerRed and lysosomal porphyrins could not induce fluorescence change of Si-DMA. This surprising selectivity of Si-DMA response depending on the Sens localization and photosensitization mechanism is caused by a limited intracellular (1)O2 diffusion distance (∼300 nm) and negligible generation of (1)O2 by type-I Sens, respectively. For the first time, we successfully visualized (1)O2 generated during PDT with a spatial resolution of a single mitochondrial tubule.

Biological applications of LbL multilayer capsules: from drug delivery to sensing

Polyelectrolyte multilayer (PEM) capsules engineered with active elements for targeting, labeling, sensing and delivery hold great promise for the controlled delivery of drugs and the development of new sensing platforms. PEM capsules composed of biodegradable polyelectrolytes are fabricated for intracellular delivery of encapsulated cargo (for example peptides, enzymes, DNA, and drugs) through gradual biodegradation of the shell components. PEM capsules with shells responsive to environmental or physical stimuli are exploited to control drug release. In the presence of appropriate triggers (e.g., pH variation or light irradiation) the pores of the multilayer shell are unlocked, leading to the controlled release of encapsulated cargos. By loading sensing elements in the capsules interior, PEM capsules sensitive to biological analytes, such as ions and metabolites, are assembled and used to detect analyte concentration changes in the surrounding environment. This Review aims to evaluate the current state of PEM capsules for drug delivery and sensing applications.