Spin-Trapping Reactions of a Novel Gauchetype Radical Trapper G-CYPMPO

Green Emissive Molybdenum Nanoclusters for Selective and Sensitive Detection of Hydroxyl Radical in Water Samples

In this work, Cassia tora (C. tora) have been used as a template to synthesize green fluorescent C. tora molybdenum nanoclusters (C. tora-MoNCs) through a green chemistry approach. These C. tora-MoNCs showed a quantum yield (QY) of 7.72% and exhibited a significant emission peak at 498 nm when excited at 380 nm. The as-prepared C. tora-MoNCs had an average size of 3.48 ± 0.80 nm and showed different surface functionality. The as-synthesized C. tora-MoNCs were successfully identified the hydroxyl radical (•OH) via a fluorescence quenching mechanism. Also, fluorescence lifetime and Stern-Volmer proved that after the addition of •OH radicals it was quenched the fluorescence intensity via a static quenching mechanism. The limit of detection is 9.13 nM, and this approach was successfully utilized for sensing •OH radicals in water samples with a good recovery rate.

Managing Encapsulated Oil Extract of Date Seed Waste for High Hydroxyl Radical Scavenging Assayed via Hybrid Photo-Mediated/Spectrofluorimetric Probing

This work addresses two research topics: the first concerns the specific/sensitive trapping of hydroxyl radicals (^•OH), and the second concerns the efficacy of encapsulating natural antioxidants, potentially lengthening their preservation activity. For context, nano-titania was solar-irradiated to produce ^•OH, which was spectrofluorimetrically assessed, based on the selective aromatic hydroxylation of the non-fluorescent sodium terephthalate to 2-hydroxyterephthalate fluorophore. Fluorescence intensity is proportional to generated ^•OH. Thus, a simple/rapid indirect method was utilized to assess ^•OH precisely. Accordingly, novel photoluminescent system is outlined in order to assess the scavenging potentiality of ^•OH in date seed oil (DSO) in both its pure and encapsulated formulations (ECP-DSO), i.e., when fresh and 5 months after extraction and encapsulation, respectively. With the addition of 80 μg/mL DSO or ECP-DSO, the efficacy of ^•OH scavenging amounted to 25.12 and 63.39%, which increased to 68.65 and 92.72% when 200 μg/mL DSO or ECP-DSO, respectively, was added. Moreover, the IC50 of DSO and ECP-DSO is 136.6 and 62.1 µg/mL, respectively. Furthermore, DSO and ECP-DSO decreased the kinetics for producing ^•OH by ≈20 and 40%, respectively, relative to ^•OH generated in the absence of antioxidant. This demonstrates the benefits of encapsulation on the preservation activity of natural antioxidants, even after five months after extraction, in terms of its interesting activity when compared to synthetic antioxidants. The developed fluorimetric ^•OH probing upgrades antioxidant medicines, thus paving the way for theoretical/practical insights on mechanistic hydroxyl radical-damaging biology.

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.

Boron-enriched rice-like homologous carbon nanoclusters with a 51.5% photoluminescent quantum yield for highly sensitive determination of endogenous hydroxyl radicals in living cells

Exploring the ultrahigh quantum efficiency of a carbon-based probe via a green and simple technique, and utilisation of its sensing ability for highly bioactive molecule detection is still highly challenging. Herein, we prepared a novel boron-enriched rice-like homologous carbon nanoclusters (BRCNs) with an ultrahigh quantum efficiency of ∼51.5% by introduction of a conjugated structure attached to the CN bond and an electron-withdrawing boron active centre. Unexpectedly, the BRCNs obtained showed a stable dispersion of rice-like carbon nanograins, composed of small carbon dot assembled nanoclusters with an average diameter size of ∼30 nm, and containing boron units of ∼24.68 at%. What's exciting is that the BRCNs obtained exhibited an "on-off-on" three-state emission with the addition of an hydroxyl radical (OH˙) and its antioxidants. Thus, two distinctive fluorescent responses for OH˙ and antioxidants based on the BRCN probe had been developed, and the mechanism has been determined using TEM, XPS, FT-IR, FL, UV-vis spectrophotometry, UPS and fluorescent lifetimes. The OH˙, generated from the Fenton's reagent, preferentially attack the electron-deficient vacancy p orbit of the boron atom in the surface of the BRCNs, which results in the boron atom being easily substituted/attacked by OH˙, and leading to spontaneous aggregation induced quenching (AIQ) due to the existence of a strong intermolecular hydrogen bond between denatured BRCNs. Furthermore, the proposed method was also successfully applied to monitor endogenous OH˙ generation in HeLa cells by confocal imaging, which could be used for elucidating OH˙-induced oxidative damage to biological tissues and proteins.

Hybrid solvothermal/sonochemical-mediated synthesis of ZnO NPs generative of OH radicals: Photoluminescent approach to evaluate OH scavenging activity of Egyptian and Yemeni Punica granatum arils extract

Zinc oxide NPs were synthesized solvothermally within sonochemical mediation and characterized by XRD, FTIR, SEM, EDX, elemental mapping, TEM and UV-vis. spectrophotometry. To evaluate the hydroxyl radicals (OH) scavenging activity of arils extract of Egyptian (EGY-PAM) and Yemeni Punica granatum (YEM-PAM), the developed zinc oxide nano particles (ZnO NPs) as a highly productive source of hydroxyl radicals (under Solar-illumination) was used. The yield of OH was trapped and probed via fluorimetric monitoring. This suits the first sensitive/selective photoluminescent avenue to evaluate the OH scavenging activity. The high percentage of DPPH radical scavenging reflected higher contents of phenolics, flavonoids, and anthocyanins that were found in EGY-PAM and YEM-PAM. Although, some secondary metabolites contents were significantly different in EGY-PAM and YEM-PAM, the traditional DPPH radical scavenging methodology revealed insignificant IC50. Unlike, the developed fluorimetric probing, sensitively discriminated the OH scavenging activity with IC50 (105.7 µg/mL) and lower rate of OH productivity (k = 0.031 min-1) in case of EGY-PAM in comparison to IC50 (153.4 µg/mL) and higher rate of OH productivity (k = 0.053 min-1) for YEM-PAM. Our findings are interestingly superior to the TBHQ that is synthetic antioxidant. Moreover, our developed methodology for fluorimetric probing of OH radicals scavenging, recommends EGY-PAM as OH radicals scavenger for diabetic patients while YEM-PAM exhibited a better OH radicals scavenging appropriate for high blood pressure patients. More interestingly, EGY-PAM and YEM-PAM exhibited high anticancer potentiality. The aforementioned OH and DPPH scavenging activities as well as the anticancer potentiality present EGY-PAM and YEM-PAM as promising sources of natural antioxidants, that may have crucial roles in some chronic diseases such as diabetics and hypertension in addition to cancer therapeutic protocols.

Detection limit of electron spin resonance for Japanese deciduous tooth enamel and density separation method for enamel-dentine separation

Electron spin resonance (ESR) dosimetry is one of the most powerful tools for radiation dose reconstruction. The detection limit of this technique using human teeth is reported to be 56 mGy or 67 mGy; however, the absorbed dose of Fukushima residents after the Fukushima Daiichi Nuclear Power Plant (FNPP) accident was estimated to be lower than this detection limit. Our aim is to assess the absorbed radiation dose of children in Fukushima Prefecture after the accident; therefore, it is important to estimate the detection limit for their teeth. The detection limit for enamel of deciduous teeth of Japanese children separated by the mechanical method is estimated to be 115.0 mGy. The density separation method can effectively separate enamel from third molars of Japanese people. As we have collected thousands of teeth from children in Fukushima, the present technique may be useful to examine their external absorbed dose after the FNPP accident.

A Unique Multifunctional Nanoenzyme Tailored for Triggering Tumor Microenvironment Activated NIR-II Photoacoustic Imaging and Chemodynamic/Photothermal Combined Therapy

The accurate diagnosis and targeted therapy of malignant tumors face significant challenges. To address these, an oxidized molybdenum polyoxometalate-copper nanocomposite (Ox-POM@Cu) is designed and synthesized here. The doping with Cu determines the formation of oxygen vacancies, which can increase the carrier concentration in Ox-POM@Cu, accelerate electron transfer, and enhance the redox activity, thus playing an efficient catalytic role. The nanocomposite presents unique enzymatic functions characterized by a multielement catalytic activity in the tumor microenvironment (TME). In addition, it can be employed as an NIR-II photoacoustic imaging (PAI) probe and cancer therapy agent. First, it participates in a redox reaction with glutathione (GSH) in tumor tissues, activates the PAI and photothermal therapy functions via NIR-II irradiation, and depletes the GSH supply in cancerous cells. Subsequently, it catalyzes a Fenton-like reaction with H₂ O₂ in tumor tissues to form hydroxyl radicals, thereby performing a chemodynamic therapy function. The findings show that the developed nanoenzyme is very efficient in the diagnosis and treatment of malignant tumors. This work not only provides a new strategy for the design of TME-induced NIR-II PAI but also presents new insights into enhanced cancer therapy.

Stability and Free Radical Production for CO2 and H2 in Air Nanobubbles in Ethanol Aqueous Solution

In this study, 8% hydrogen (H₂) in argon (Ar) and carbon dioxide (CO₂) gas nanobubbles was produced at 10, 30, and 50 vol.% of ethanol aqueous solution by the high-speed agitation method with gas. They became stable for a long period (for instance, 20 days), having a high negative zeta potential (−40 to −50 mV) at alkaline near pH 9, especially for 10 vol.% of ethanol aqueous solution. The extended Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory was used to evaluate the nanobubble stability. When the nanobubble in ethanol alkaline aqueous solution changed to an acidic pH of around 5, the zeta potential of nanobubbles was almost zero and the decrease in the number of nanobubbles was identified by the particle trajectory method (Nano site). The collapsed nanobubbles at zero charge were detected thanks to the presence of few free radicals using G-CYPMPO spin trap reagent in electron spin resonance (ESR) spectroscopy. The free radicals produced were superoxide anions at collapsed 8%H₂ in Ar nanobubbles and hydroxyl radicals at collapsed CO₂ nanobubbles. On the other hand, the collapse of mixed CO₂ and H₂ in Ar nanobubble showed no free radicals. The possible presence of long-term stable nanobubbles and the absence of free radicals for mixed H₂ and CO₂ nanobubble would be useful to understand the beverage quality.

[Generation, Detection and Bio-protection of Reactive Oxygen Species/Free Radicals]

In the present paper, generation, detection and protection of reactive oxygen species (ROS)/free radicals in relation to the author's research over about 20 years are reviewed. ROS/free radicals are generally generated physically, chemically and biologically, and they are harmful to living organisms by inducing various disorders and diseases. To prevent the harmful effects of ROS/free radicals, antioxidants are believed to be useful. Among many methods to detect ROS/free radicals, ESR technique is a direct method and is described in detail in this review. Several topics such as the production of ROS/free radicals by low temperature atmospheric pressure plasma, the evaluation of antioxidant activity using hemolysis of erythrocytes and the protective effects of antioxidants against X-ray induced damage to mice, are presented.

Activatable Second Near-Infrared Fluorescent Probes: A New Accurate Diagnosis Strategy for Diseases

Recently, second near-infrared (NIR-II) fluorescent imaging has been widely applied in biomedical diagnosis, due to its high spatiotemporal resolution and deep tissue penetration. In contrast to the "always on" NIR-II fluorescent probes, the activatable NIR-II fluorescent probes have specific targeting to biological tissues, showing a higher imaging signal-to-background ratio and a lower detection limit. Therefore, it is of great significance to utilize disease-associated endogenous stimuli (such as pH values, enzyme existence, hypoxia condition and so on) to activate the NIR-II probes and achieve switchable fluorescent signals for specific deep bioimaging. This review introduces recent strategies and mechanisms for activatable NIR-II fluorescent probes and their applications in biosensing and bioimaging. Moreover, the potential challenges and perspectives of activatable NIR-II fluorescent probes are also discussed.

Effects of loading a magnetic field longitudinal to the linear particle-beam track on yields of reactive oxygen species in water

The effects of a magnetic field longitudinal to the ion beam track on the generation of hydroxyl radicals (•OH) and hydrogen peroxide (H₂O₂) in water were investigated. A longitudinal magnetic field was reported to enhance the biological effects of the ion beam. However, the mechanism of the increased cell death by a longitudinal magnetic field has not been clarified. The local density of •OH generation was estimated by a method based on the EPR spin-trapping. A series of reaction mixtures containing varying concentrations (0.76‒2278 mM) of DMPO was irradiated by 16 Gy of carbon- or iron-ion beams at the Heavy-Ion Medical Accelerator in Chiba (HIMAC, NIRS/QST, Chiba, Japan) with or without a longitudinal magnetic field (0.0, 0.3, or 0.6 T). The DMPO-OH yield in the sample solutions was measured by X-band EPR and plotted versus DMPO density. O₂-dependent and O₂-independent H₂O₂ yields were measured. An aliquot of ultra-pure water was irradiated by carbon-ion beams with or without a longitudinal magnetic field. Irradiation experiments were performed under air or hypoxic conditions. H₂O₂ generation in irradiated water samples was quantified by an EPR spin-trapping, which measures •OH synthesized from H₂O₂ by UVB irradiation. Relatively sparse •OH generation caused by particle beams in water were not affected by loading a magnetic field on the beam track. O₂-dependent H₂O₂ generation decreased and oxygen-independent H₂O₂ generation increased after loading a magnetic field parallel to the beam track. Loading a magnetic field to the beam track made •OH generation denser or made dense •OH more reactive.

Free radical degradation in aqueous solution by blowing hydrogen and carbon dioxide nanobubbles

The main findings are the hydroxyl radical scavenging and the superoxide anion diminishing by mixing the carbon dioxide (CO₂) nanobubbles after hydrogen nanobubble blowing in water and alcohol aqueous solution. The nanobubbles produce the hydroxyl radical by ultrasonic waves, changing the pH and catalyst and so on, while the nanobubble is very reactive to scavenge free radicals. In this research especially hydrogen (4% H₂ in argon) and CO₂ nanobubbles have been blown into hydrogen peroxide (H₂O₂) added pure water, ethanol, and ethylene glycol aqueous solution through a porous ceramic sparger from the gas cylinder. The aqueous solutions with H₂O₂ are irradiated by ultraviolet (UV) light and the produced hydroxyl radical amount is measured with spin trapping reagent and electron spin resonance (ESR). The CO₂ nanobubble blowing extremely has reduced the hydroxyl radical in water, ethanol, and ethylene glycol aqueous solution. On the other hand, when H₂ nanobubbles are brown after CO₂ nanobubble blowing, the hydroxyl radical amount has increased. For the disinfection test, the increase of hydroxyl radicals is useful to reduce the bacteria by the observation in the agar medium. Next, when the superoxide anion solution is mixed with nanobubble containing water, ethanol, and ethylene glycol aqueous solution, H₂ nanobubble has reduced the superoxide anion slightly. The water containing both CO₂ and H₂ nanobubble reduces the superoxide anion. The less than 20% ethanol and the 30% ethylene glycol aqueous solution containing CO₂ nanobubbles generated after H₂ nanobubble blowing can diminish the superoxide anion much more. While the H₂ nanobubble blowing after CO₂ nanobubble blowing scavenges the superoxide anion slightly. The experimental results have been considered using a chemical reaction formula.

Dual-emission copper nanoclusters-based ratiometric fluorescent probe for intracellular detection of hydroxyl and superoxide anion species

A fluorescent nanoprobe based on copper nanoclusters (CuNCs) has been developed for ratiometric detection of hydroxyl radicals (^•OH) and superoxide anion radicals (O₂^•-). Two differently luminescent CuNCs, namely cyan-emissive poly(methacrylic acid)-protected copper nanoclusters (PCuNCs) and orange-emissive bovine serum albumin-protected CuNCs (BCuNCs), were conjugated to obtain a hybrid, dual-emission nanoprobe (PCuNCs-BCuNCs) with the corresponding peaks at 445 nm and 652 nm at an excitation wavelength of 360 nm. In particular, the fluorescence peak at 445 nm gradually enhanced with the incremental addition of ^•OH and O₂^•-. However, the fluorescence emission at 652 nm was greatly quenched in the presence of ^•OH, while in case of O₂^•-, the fluorescence intensity remained constant. The differential response of the PCuNCs-BCuNCs towards ^•OH and O₂^•- formed the basis of ratiometric detection. Under optimal conditions, the PCuNCs-BCuNCs exhibited good sensitivity and linearity towards ^•OH and O₂^•- with limits of detection of 0.15 μM and 1.8 μM, respectively. Moreover, the nanoprobe exhibited high selectivity for ^•OH and O₂^•- over other potential ROS interferences. Besides, PCuNCs-BCuNCs were eventually applied for qualitative and quantitative ratiometric assessment of intracellular ^•OH and O₂^•- in L-132 cells. Therefore, this strategy unveils a new potential for copper nanocluster-based sensing of ROS.

Dynamic Detection of Endogenous Hydroxyl Radicals at Single-Cell Level with Individual Ag-Au Nanocages

Hydroxyl radicals (•OH) are a type of short-lived radical which is the most aggressive reactive oxygen species due to its high reactivity to biomolecules. Dynamic measurement of •OH level in living cells is critical for understanding cell physiology and pathology. In this manuscript, we prepare individual Ag-Au@PEG/RGD nanocages for in situ determination of endogenous •OH at single-cell level, whose spectral shift rate correlate to the •OH concentration. The high-selective response to •OH relies on the specific oxidization of the conjugated PEG/RGD outside and the silver etching inside the nanocages that resulted in a significant LSPR signal and scattered color changes. The spectral red-shift rate of LSPR has a linear relationship with the logarithm of •OH concentration in range of 100 pM to 1 μM, suitable for the measurement of endogenous •OH. Thus, the individual nanocages were successfully used to monitor the dynamic intracellular •OH level of single tumor cells under oxidative stress. This strategy has great potential in promoting •OH mediated cell homeostasis and injury research.

Indolenine-Based Derivatives as Customizable Two-Photon Fluorescent Probes for pH Bioimaging in Living Cells

Novel pH probes based on 2-(6-methoxynaphthalen-2-yl)-3,3-dimethyl-3H-indole have been synthesized and characterized. These compounds display excellent "off-on" fluorescence responses to acidic pH especially under two-photon (TP) excitation conditions as well as strong selectivity and sensitivity toward H⁺. These features are supported by fluorescence quantum yields over 35%, TP cross sections ∼60 GM, and good resistance to photodegradation under acidic conditions. The synthetic versatility of this model allows subcellular targets to be tuned through minor scaffold modifications without affecting its optical characteristics. The effectiveness of the probes' innate photophysical properties and the structural modifications for different pH-related applications are demonstrated in mouse embryonic fibroblast cells.

A highly selective and sensitive upconversion nanoprobe for monitoring hydroxyl radicals in living cells and the liver

Excessive reactive oxygen species (ROS) would attack living cells and cause a series of oxidative stress related diseases, such as liver damage. Hydroxyl radicals (·OH) are currently known as one of the most toxic and harmful free radicals to organisms. Therefore, studies involving hydroxyl radicals have become important research topics in the fields of biology, biochemistry, and biomedicine. In addition, imaging of analytes using upconversion nanoparticles (UCNPs) possesses significant advantages over that using general fluorescent dyes or nanoparticles due to its high spatial resolution, reduced photodamage, and deep tissue penetration properties. Herein, we designed a highly selective and sensitive hydroxyl radical nanoprobe based on the luminescence resonance energy transfer between upconversion nanoparticles and methylene blue (MB). The concentration of ·OH could be determined by the fluorescence recovery of the UCNPs due to the oxidative damage of MB. Using this nanoprobe, the ·OH in living cells or in liver tissues could be monitored with high sensitivity and selectivity.

In situ detection of hydroxyl radicals in mitochondrial oxidative stress with a nanopipette electrode

A nanopipette sensor was designed for the in situ detection of ˙OH around mitochondria with high selectivity and sensitivity.

A sensitive BODIPY-based fluorescent probe for detecting endogenous hydroxyl radicals in living cells

A novel “turn-on” NIR fluorescent probe was designed and used for monitoring endogenous hydroxyl radical in living cells, which also showed higher selectivity toward hydroxyl radical over other reactive oxygen/nitrogen species.

Removal of Banana Tree Fungi Using Green Tuff Rock Powder Waste Containing Zeolite

Hinai green tuff, which is found in Akita Prefecture, Japan, is used for the production of building materials, etc. About 60% of all stone is emitted as waste powder and therefore it is important to find ways for recycling it. In this work, the characteristics of green tuff powder have been investigated. The results of scanning electron microscope (SEM) and elemental map observations indicate that the green tuff contains TiO2 on zeolite. The green tuff can therefore be used as a natural catalyst for producing hydrogen peroxide with moisture and oxygen with light. The optimum calcined temperature of the green tuff powder is about 800 °C, producing the hydroxyl radical from hydrogen peroxide decomposition without ultraviolet light (UV) and decomposition of the superoxide anion. As the application of green tuff powder, Cavendish banana trees found in the Philippines infected by a new Panama disease were treated with powder suspension in order to remove the fungus (a type of Fusarium wilt) due to the photocatalyst characteristics of powder. The suspension, prepared by using the powder was sprayed on the infected banana trees for about one month. Photograph observation indicated that the so-called 800 °C suspension spray was more effective in growing the infected banana trees.

A novel electrochemical sensor for determination of hydroxyl radicals in living cells by coupling nanoporous gold layer with self-assembled 6-(Ferrocenyl) hexanethiol

The detection of hydroxyl radicals (•OH) in live cells is significant to study its physiological and pathological roles, while it is full of challenge due to the extremely low concentration and short lifetime of •OH. Herein, we have developed a novel electrochemical sensor based on 6-(Ferrocenyl) hexanethiol (6-FcHT) self-assembled nanoporous gold layer (NPGL) modified GE (6-FcHT/NPGL/GE), which can detect the release of •OH from living cells with high sensitivity and selectivity. The superior sensitivity can stem from the unique porous architecture of NPGL, which enlarged electrode surface area and expedited electron transportation during electrochemical reactions. Additionally, NPGL provides more active binding sites for the assembly of capture agent (6-FcHT) of •OH, thus ensuring high selectivity. For comparison, 6-FcHT/GE was applied to detect •OH, and the obtained sensitivity was 0.0305 mA nM^-1 and detection limit was 0.133 nM in the linear range of 0.4 nM-70 nM. After modification of NPGL, the sensitivity of 6-FcHT/NPGL/GE to the •OH response was increased to 0.1364 mA nM^-1, detection limit was reduced to 0.316 pM and the linear range was extended from 1 pM to 100 nM. It is worth mentioning that a plenty of extra merits has also been validated like reproducibility, repeatability and stability, enabling to direct electrochemical detection of •OH in HepG2 cells.

Production of the Hydroxyl Radical and Removal of Formaldehyde by Calcined Green Tuff Powder and Tile

Waste green tuff powder produced by cutting Towada stone has been utilized to eliminate formaldehyde related to greenhouse gases. The green tuff contains TiO2 on zeolite as observed by scanning electron microscope (SEM)t. The green tuff is a natural catalyst that can produce hydrogen peroxide with moisture and oxygen with light. The optimum temperature for calcination of the green tuff powder has been investigated in order to produce hydroxyl radicals from the decomposition of hydrogen peroxide using ultraviolet light (UV) and no light. The green tuff calcined at 800 °C showed a high decomposition rate of hydrogen peroxide with no UV light under high alkaline conditions when measured by using ESR. With UV light, the optimum temperature for calcination of green tuff powder in order to reduce the hydroxyl radical was also 800 °C. Next, the powder calcined at 800 °C was used to produce the tile by compression and heating, and then the formaldehyde adsorption rate was measured. The green tuff powder calcined at 800 °C showed a high adsorption rate, similar to that of the activated carbon. The tiles formed at 40 MPa and heated at 1100 °C were the strongest and also showed adsorption with respect to formaldehyde. The adsorbed formaldehyde on the green tuff tile and powder was possibility decomposed by the hydroxyl radical produced by photocatalysis.

Novel Cyanostilbene-Based Fluorescent Chemoprobe for Hydroxyl Radicals and Its Two-Photon Bioimaging in Living Cells

A novel cyanostilbene derivative as a selective fluorescent chemoprobe for hydroxyl radicals was synthesized. The chemoprobe shows strong green emission in aqueous solution with the addition of hydroxyl radicals. Conversely, negligible emission changes are observed upon addition of other reactive oxygen species. The chemoprobe 1 shows high sensitivity, having the low detection limit of ∼1.0 × 10^-7 M. Furthermore, the fluorescent chemoprobe exhibits low cytotoxicity and is effectively applied to bioimaging of hydroxyl radicals by two-photon confocal microscopy in HeLa cells. These results indicate that the new chemoprobe has great potential for bioimaging in vivo and in vitro systems.

Double signal amplification through a functionalized nanoporous Au–Ag alloy microwire and Au nanoparticles: development of an electrochemical ˙OH sensor based on a self-assembled layer of 6-(ferrocenyl)hexanethiol

Novel electrochemical sensors were developed based on a FcHT functionalized NPAMW and AuNPs for the analysis of ˙OH released from live cells.

Fluorescent TPA@GQDs Probe for Sensitive Assay and Quantitative Imaging of Hydroxyl Radicals in Living Cells

A fluorescent probe TPA@GQDs is fabricated by the conjugation of terephthalic acid (TPA) on the surface of graphene quantum dots (GQDs). The TPA@GQDs probe not only has favorable dispersibility but also exhibits excellent fluorescence stability over a wide pH range and high ionic strength and favorable antiphotobleaching ability. The great fluorescence enhancement of TPA@GQDs induced by the reaction between TPA and hydroxyl radicals makes the TPA@GQDs a powerful probe for the sensitive assay of hydroxyl radicals, giving rise to a low detection limit down to 12 nmol L^-1. Meanwhile, the obtained fluorescent TPA@GQDs probe shows low cytotoxicity and favorable biocompatibility. Its potential in bioimaging is demonstrated by the quantitative fluorescent imaging of hydroxyl radicals in living HeLa cells under different circumstances, which enables the opportunities to study hydroxyl radicals dynamics in living cells.

Improvement of the method to estimate the relative reaction rate constants of hydroxyl radical with polyphenols using ESR spin trap: X-ray irradiation of water with a flowing system

UV-photolysis of hydrogen peroxide is a useful technique to produce hydroxyl radical. However, it is not an appropriate method to estimate the reactivity of polyphenols with hydroxyl radicals because many of the polyphenol derivatives also absorb the UV-light to generate hydroxyl radicals. In this study, X-ray irradiation of water with a flowing system was applied to estimate the reactivity of hydroxyl radicals with polyphenols using electron spin resonance (ESR) spin trap. The obtained relative reaction rates reasonably agreed with previous data by pulse radiolysis. This method will be a useful technique to estimate the reactivity of antioxidants including polyphenols with hydroxyl radicals.

A Rationally Designed Upconversion Nanoprobe for in Vivo Detection of Hydroxyl Radical

The detection of •OH in live organisms is crucial to the understanding of its physiological and pathological roles; while this is too challenging because of the extremely low concentration and high reactivity of the species in the body. Herein, we report the rational design and fabrication of an NIR-light excited luminescence resonance energy transfer-based nanoprobe, which for the first time realizes the in vivo detection of •OH. The nanoprobe is composed of two moieties: upconversion nanoparticles with sandwich structure and bared surface as the energy donor; and mOG, a modified azo dye with tunable light absorption, as both the energy acceptor and the •OH recognizing ligand. The as-constructed nanoprobe exhibited ultrahigh sensitivity (with the quantification limit down to 1.2 femtomolar, several orders of magnitude lower than that of most previous •OH probes), good biocompatibility, and specificity. It was successfully used for monitoring [•OH] levels in live cells and tissues.

Ratiometric fluorescence probe for monitoring hydroxyl radical in live cells based on gold nanoclusters

Determination of hydroxyl radical ((•)OH) with high sensitivity and accuracy in live cells is a challenge for evaluating the role that (•)OH plays in the physiological and pathological processes. In this work, a ratiometric fluorescence biosensor for (•)OH was developed, in which gold nanocluster (AuNC) protected by bovine serum albumin was employed as a reference fluorophore and the organic molecule 2-[6-(4'-hydroxy)phenoxy-3H-xanthen-3-on-9-yl]benzoic acid (HPF) acted as both the response signal and specific recognition element for (•)OH. In the absence of (•)OH, only one emission peak at 637 nm ascribed to AuNCs was observed, because HPF was almost nonfluorescent. However, fluorescence emission at 515 nm attributed to the HPF product after reaction with (•)OH--dianionic fluorescein--gradually increased with the continuous addition of (•)OH, while the emission at 637 nm stays constant, resulting in a ratiometric determination of (•)OH. The developed fluorescent sensor exhibited high selectivity for (•)OH over other reactive oxygen species (ROS), reactive nitrogen species (RNS), metal ions, and other biological species, as well as high accuracy and sensitivity with low detection limit to ∼0.68 μM, which fulfills the requirements for detection of (•)OH in a biological system. In addition, the AuNC-based inorganic-organic probe showed long-term stability against light illumination and pH, good cell permeability, and low cytotoxicity. As a result, the present ratiometric sensor was successfully used for bioimaging and monitoring of (•)OH changes in live cells upon oxidative stress.

Highly sensitive free radical detection by nitrone-functionalized gold nanoparticles

The detection of free radicals and related species has attracted significant attention in recent years because of their critical roles in physiological and pathological processes. Among the methods for the detection of free radicals, electron spin resonance (ESR) coupled with the use of the spin trapping technique has been an effective approach for characterization and quantification of these species due to its high specificity. However, its application in biological systems, especially in in vivo systems, has been greatly limited partially due to the low reaction rate between the currently available spin traps with biological radicals. To overcome this drawback, we herein report the first example of nitrone functionalized gold nanoparticles (Au@EMPO) as highly efficient spin traps in which the thiolated EMPO (2-(ethoxycarbonyl)-2-methyl-3,4-dihydro-2H-pyrrole 1-oxide) derivative was self-assembled on gold nanoparticles. Kinetic studies showed that Au@EMPO has a 137-fold higher reaction rate constant with ˙OH than PBN (N-tert-butyl-α-phenylnitrone). Owing to the high rate of trapping ˙OH by Au@EMPO as well as the high stability of the resulting spin adduct (t½ ∼ 56 min), Au@EMPO affords 124-fold higher sensitivity for ˙OH than EMPO. Thus, this new nanospin trap shows great potential in trapping the important radicals such as ˙OH in various biological systems and provides a novel strategy to design spin traps with much improved properties.