A selective, cell-permeable optical probe for hydrogen peroxide in living cells

Reaction-based indicator displacement assay (RIA) for the colorimetric and fluorometric detection of hydrogen peroxide

Reaction-based indicator displacement assay for the optical cycle-monitoring of hydrogen peroxide.

Mesoporous silica nanoparticles for stimuli-responsive controlled drug delivery: advances, challenges, and outlook

With the development of nanotechnology, the application of nanomaterials in the field of drug delivery has attracted much attention in the past decades. Mesoporous silica nanoparticles as promising drug nanocarriers have become a new area of interest in recent years due to their unique properties and capabilities to efficiently entrap cargo molecules. This review describes the latest advances on the application of mesoporous silica nanoparticles in drug delivery. In particular, we focus on the stimuli-responsive controlled release systems that are able to respond to intracellular environmental changes, such as pH, ATP, GSH, enzyme, glucose, and H2O2. Moreover, drug delivery induced by exogenous stimuli including temperature, light, magnetic field, ultrasound, and electricity is also summarized. These advanced technologies demonstrate current challenges, and provide a bright future for precision diagnosis and treatment.

A NIR fluorescent probe: imaging endogenous hydrogen peroxide during an autophagy process induced by rapamycin

In this work, a near-infrared probe (Cy-B) with high sensitivity, and good specificity as well as photo-stability has been developed for monitoring both exogenous and endogenous H₂O₂ in living cells. To the best of our knowledge, it was applied successfully for the first time to monitor spontaneous hydrogen peroxide in an autophagy process induced by the stimulation of rapamycin. The mice imaging experiments indicate that the probe has a good potential to be employed in the imaging of living biological systems.

A non-enzymatic amperometric hydrogen peroxide sensor based on iron nanoparticles decorated reduced graphene oxide nanocomposite

A simple and facile green process was used for the synthesis of iron nanoparticles (FeNPs) decorated reduced graphene oxide (rGO) nanocomposite by using Ipomoea pes-tigridis leaf extract as a reducing and stabilizing agent. The as-prepared rGO/FeNPs nanocomposite was characterized by transmission electron microscopy, X-ray spectroscopy and Fourier transform infrared spectroscopy. The nanocomposite was further modified on the glassy carbon electrode and used for non-enzymatic sensing of hydrogen peroxide (H₂O₂). Cyclic voltammetry results reveal that rGO/FeNPs nanocomposite has excellent electro-reduction behavior to H₂O₂ when compared to the response of FeNPs and rGO modified electrodes. Furthermore, the nanocomposite modified electrode shows 9 and 6 folds enhanced reduction current response to H₂O₂ than that of rGO and FeNPs modified electrodes. Amperometric method was further used to quantify the H₂O₂ using rGO/FeNPs nanocomposite, and the response was linear over the concentration ranging from 0.1μM to 2.15mM. The detection limit and sensitivity of the sensor were estimated as 0.056μM and 0.2085μAμM^-1cm^-2, respectively. The fabricated sensor also utilized for detection of H₂O₂ in the presence of potentially active interfering species, and found high selectivity towards H₂O₂.

Alcohol, Aldehyde, and Ketone Liberation and Intracellular Cargo Release through Peroxide-Mediated α-Boryl Ether Fragmentation

α-Boryl ethers, carbonates, and acetals, readily prepared from the corresponding alcohols that are accessed through ketone diboration, react rapidly with hydrogen peroxide to release alcohols, aldehydes, and ketones through the collapse of hemiacetal intermediates. Experiments with α-boryl acetals containing a latent fluorophore clearly demonstrate that cargo can be released inside cells in the presence of exogenous or endogenous hydrogen peroxide. These experiments show that this protocol can be used for drug activation in an oxidative environment without generating toxic byproducts.

Reactive Oxygen Species: A Key Hallmark of Cardiovascular Disease

Cardiovascular diseases (CVDs) have been the prime cause of mortality worldwide for decades. However, the underlying mechanism of their pathogenesis is not fully clear yet. It has been already established that reactive oxygen species (ROS) play a vital role in the progression of CVDs. ROS are chemically unstable reactive free radicals containing oxygen, normally produced by xanthine oxidase, nicotinamide adenine dinucleotide phosphate oxidase, lipoxygenases, or mitochondria or due to the uncoupling of nitric oxide synthase in vascular cells. When the equilibrium between production of free radicals and antioxidant capacity of human physiology gets altered due to several pathophysiological conditions, oxidative stress is induced, which in turn leads to tissue injury. This review focuses on pathways behind the production of ROS, its involvement in various intracellular signaling cascades leading to several cardiovascular disorders (endothelial dysfunction, ischemia-reperfusion, and atherosclerosis), methods for its detection, and therapeutic strategies for treatment of CVDs targeting the sources of ROS. The information generated by this review aims to provide updated insights into the understanding of the mechanisms behind cardiovascular complications mediated by ROS.

Simultaneous fluorescence imaging of hydrogen peroxide in mitochondria and endoplasmic reticulum during apoptosis

Cell apoptosis is a biochemical and molecular pathway essential for maintaining cellular homeostasis. It is an integrated process involving in a series of signal transduction cascades. Moreover, the apoptotic pathways may be initiated inside various subcellular organelles. Increasing evidence indicates that hydrogen peroxide (H2O2) is closely related to cell apoptosis, particularly in the mitochondria. However, during the apoptotic process, the synergetic variation of H2O2 levels in different compartments is seldom explored, particularly in two important organelles: mitochondria and endoplasmic reticulum (ER). To solve this problem, we developed two new organelle-specific fluorescent probes termed MI-H2O2 and ER-H2O2 that can detect H2O2 in mitochondria and ER, respectively or simultaneously. Experimental results demonstrated that MI-H2O2 and ER-H2O2 display distinguishable excitation and emission spectra, as well as excellent organelle targeting capabilities. Therefore, we used MI-H2O2 and ER-H2O2 to successfully image exogenous or endogenous hydrogen peroxide in the mitochondria and ER. Interestingly, during diverse apoptotic stimuli, dual-color fluorescence imaging results revealed that the changes of H2O2 levels in mitochondria and ER are different. The H2O2 levels are enhanced in both the mitochondria and ER during the l-buthionine sulfoximine (BSO)-treated cell apoptosis process. During mitochondria-oriented apoptosis induced by carbonyl cyanide m-chlorophenylhydrazone (CCCP) or rotenone, H2O2 levels prominently and continuously increase in the mitochondria, whereas the ER H2O2 levels were found to rise subsequently after a delay. Moreover, during ER-oriented apoptosis induced by tunicamycin, ER is the major site for overproduction of H2O2, and delayed elevation of the H2O2 levels was found in the mitochondria. Altogether, this dual-probe and multicolor imaging approach may offer a proven methodology for studying molecular communication events on H2O2-related apoptosis and also other physiological and pathological processes within different subcellular organelles.

Integrated High-Content Quantification of Intracellular ROS Levels and Mitochondrial Morphofunction

Oxidative stress arises from an imbalance between the production of reactive oxygen species (ROS) and their removal by cellular antioxidant systems. Especially under pathological conditions, mitochondria constitute a relevant source of cellular ROS. These organelles harbor the electron transport chain, bringing electrons in close vicinity to molecular oxygen. Although a full understanding is still lacking, intracellular ROS generation and mitochondrial function are also linked to changes in mitochondrial morphology. To study the intricate relationships between the different factors that govern cellular redox balance in living cells, we have developed a high-content microscopy-based strategy for simultaneous quantification of intracellular ROS levels and mitochondrial morphofunction. Here, we summarize the principles of intracellular ROS generation and removal, and we explain the major considerations for performing quantitative microscopy analyses of ROS and mitochondrial morphofunction in living cells. Next, we describe our workflow, and finally, we illustrate that a multiparametric readout enables the unambiguous classification of chemically perturbed cells as well as laminopathy patient cells.

Physical, Chemical, and Biological Structures based on ROS-Sensitive Moieties that are Able to Respond to Oxidative Microenvironments

Reactive oxygen species (ROS) (H2 O2 , OCl(-) , (•) OH, O2 (-) ) are a family of reactive molecules that are generated intracellularly and are engaged in many biological processes. In physiological concentrations, ROS act as signaling molecules to a number of metabolic pathways; however, in excess they can be harmful to living organisms. Overproduction of ROS has been related to many pathophysiological conditions and a number of studies have been reported in elucidating their mechanism in these conditions. With the aim of harnessing this role, a number of imaging tools and therapeutic compounds have been developed. Here these imaging and therapeutic tools are reviewed and particularly those structures with ROS-sensitivity based on their biomedical applications and their functional groups. There is also a brief discussion about the method of preparation as well as the mechanism of action.

A benzo-15-crown-5-modifying ratiometric-absorption and fluorescent OFF-ON chemosensor for Cu(2.)

One new benzo-15-crown-5-modifying fluorene Schiff base (FBC), together with the CN-linked fluorene-3,4-dimethoxybenzene (FBDMO) and fluorene-benzene (FB) references, has been designed and facilely synthesized. The binding of Cu(2+) with nitrogen atom of CN moiety in these three compounds can inhibit the photo-induced electronic transition process and induce the ratiometric-absorption and fluorescent OFF-ON response to Cu(2+). Whereas the employment of benzo-15-crown-5 moiety in FBC as additional binding platform for Cu(2+) not only amplifies the fluorescent enhancement of FBCvia preventing the isomerization of CN moiety, but also endows this compound high selectivity and rapid response towards Cu(2+) over the references FB and FBDMO. These results render FBC highly sensitive ratiometric-absorption and fluorescent OFF-ON detecting potential for Cu(2+) with the detection limit of 3.91 × 10(-6) M.

Selective and Reversible Approaches Toward Imaging Redox Signaling Using Small-Molecule Probes

SIGNIFICANCE

Recent research has identified key roles for reactive oxygen species (ROS)/reactive nitrogen species (RNS) in redox signaling, but much remains to be uncovered. Molecular imaging tools to study these processes must not only be selective to enable identification of the ROS/RNS involved but also reversible to distinguish signaling processes from oxidative stress. Fluorescent sensors offer the potential to image such processes with high spatial and temporal resolution.

RECENT ADVANCES

A broad array of strategies has been developed that enable the selective sensing of ROS/RNS. More recently, attention has turned to the design of reversible small-molecule sensors of global redox state, with a further set of probes capable of reversible sensing of individual ROS/RNS.

CRITICAL ISSUES

In this study, we discuss the key challenges in achieving simultaneous detection of reversible oxidative bursts with unambiguous determination of a particular ROS/RNS.

FUTURE DIRECTIONS

We have highlighted key design features of small-molecule probes that show promise in enabling the study of redox signaling, identifying essential parameters that must be assessed for any new probe. Antioxid. Redox Signal. 24, 713-730.

Characterization of Fluorescein-Based Monoboronate Probe and Its Application to the Detection of Peroxynitrite in Endothelial Cells Treated with Doxorubicin

Boronate probes have emerged recently as a versatile tool for the detection of reactive oxygen and nitrogen species. Here, we present the characterization of a fluorescein-based monoboronate probe, a 4-(pinacol boronate)benzyl derivative of fluorescein methyl ester (FBBE), that proved to be useful to detect peroxynitrite in cell culture experiments. The reactivity of FBBE toward peroxynitrite as well hypochlorite, hydrogen peroxide, and tyrosyl hydroperoxide was determined. Second-order rate constants of the reactions of FBBE with peroxynitrite, HOCl, and H2O2 at pH 7.4 were equal to (2.8 ± 0.2) × 10(5) M(-1) s(-1), (8.6 ± 0.5) × 10(3) M(-1) s(-1), and (0.96 ± 0.03) M(-1) s(-1), respectively. The presence of glutathione completely blocked the oxidation of the probe by HOCl and significantly inhibited its oxidation by H2O2 and tyrosyl hydroperoxide but not by peroxynitrite. The oxidative conversion of the probe was also studied in the systems generating singlet oxygen, superoxide radical anion, and nitric oxide in the presence and absence of glutathione. Spectroscopic characterization of FBBE and its oxidation product has been also performed. The differences in the reactivity pattern were supported by DFT quantum mechanical calculations. Finally, the FBBE probe was used to study the oxidative stress in endothelial cells (Ea.hy926) incubated with doxorubicin, a quinone anthracycline antibiotic. In endothelial cells pretreated with doxorubicin, FBBE was oxidized, and this effect was reversed by PEG-SOD and L-NAME but not by catalase.

New Dioxaborolane Chemistry Enables [(18)F]-Positron-Emitting, Fluorescent [(18)F]-Multimodality Biomolecule Generation from the Solid Phase

New protecting group chemistry is used to greatly simplify imaging probe production. Temperature and organic solvent-sensitive biomolecules are covalently attached to a biotin-bearing dioxaborolane, which facilitates antibody immobilization on a streptavidin-agarose solid-phase support. Treatment with aqueous fluoride triggers fluoride-labeled antibody release from the solid phase, separated from unlabeled antibody, and creates [(18)F]-trifluoroborate-antibody for positron emission tomography and near-infrared fluorescent (PET/NIRF) multimodality imaging. This dioxaborolane-fluoride reaction is bioorthogonal, does not inhibit antigen binding, and increases [(18)F]-specific activity relative to solution-based radiosyntheses. Two applications are investigated: an anti-epithelial cell adhesion molecule (EpCAM) monoclonal antibody (mAb) that labels prostate tumors and Cetuximab, an anti-epidermal growth factor receptor (EGFR) mAb (FDA approved) that labels lung adenocarcinoma tumors. Colocalized, tumor-specific NIRF and PET imaging confirm utility of the new technology. The described chemistry should allow labeling of many commercial systems, diabodies, nanoparticles, and small molecules for dual modality imaging of many diseases.

Three-dimensional WS2 nanosheet networks for H2O2 produced for cell signaling

Hydrogen peroxide (H2O2) is an important molecular messenger for cellular signal transduction. The capability of direct probing of H2O2 in complex biological systems can offer potential for elucidating its manifold roles in living systems. Here we report the fabrication of three-dimensional (3D) WS2 nanosheet networks with flower-like morphologies on a variety of conducting substrates. The semiconducting WS2 nanosheets with largely exposed edge sites on flexible carbon fibers enable abundant catalytically active sites, excellent charge transfer, and high permeability to chemicals and biomaterials. Thus, the 3D WS2-based nano-bio-interface exhibits a wide detection range, high sensitivity and rapid response time for H2O2, and is capable of visualizing endogenous H2O2 produced in living RAW 264.7 macrophage cells and neurons. First-principles calculations further demonstrate that the enhanced sensitivity of probing H2O2 is attributed to the efficient and spontaneous H2O2 adsorption on WS2 nanosheet edge sites. The combined features of 3D WS2 nanosheet networks suggest attractive new opportunities for exploring the physiological roles of reactive oxygen species like H2O2 in living systems.

Carbazole-based two-photon fluorescent probe for selective imaging of mitochondrial hydrogen peroxide in living cells and tissues

The two-photon imaging in living cells and tissue demonstrated that the prepared probe possessed high specificity for mitochondrial H₂O₂.

A novel SERS nanoprobe for the ratiometric imaging of hydrogen peroxide in living cells

Via the assembly of 4-mercaptophenylboronic ester on the gold nanorod's surface, a novel ratiometric SERS nanosensor for H₂O₂ imaging in living cells or cancer tissues has been developed in the present study.

Determination of hypochlorite by quenching the fluorescence of 1-pyrenylboronic acid in tap water

In neutral conditions, a new probe based on the oxidative conversion of 1-pyrenylboronic acid to 1-hydroxypyrene was established for the fluorescence signaling of practical hypochlorite.

A new water-soluble and colorimetric fluorescent probe for highly sensitive detection of organophosphorus pesticides

A new water-soluble fluorescent probe bearing 1,8-naphthalimide dye, a quaternary ammonium salt and a boronate group was developed for the detection of organophosphorus pesticides.

A near-infrared fluorescent aza-bodipy probe for dual-wavelength detection of hydrogen peroxide in living cells

A boronic acid functionalized aza-borondipyrromethene dye (azaBDPBA) was applied to the dual-wavelength detection of hydrogen peroxide with high selectivity, which was loaded into cells to indicate the alteration of intracellular hydrogen peroxide during biological processes.

A novel δ-MnO2 with carbon nanotubes nanocomposite as an enzyme-free sensor for hydrogen peroxide electrosensing

We have reported the synthesis and application of carbon nanotubes supported δ-MnO₂ (δ-MnO₂/CNTs) nanocomposite as enzyme-free sensor for the detection of H₂O₂, where δ-MnO₂ serves as the catalytic center and CNTs as the highly conductive base.

Mimicking vanadium haloperoxidases: vanadium(iii)–carboxylic acid complexes and their application in H2O2 detection

Two vanadium(iii) complexes were synthesized. Hydrogen peroxide was detected by a colorimetric method based on catalytic bromination reactions with the complexes as catalysts.

A dialdehyde–diboronate-functionalized AIE luminogen: design, synthesis and application in the detection of hydrogen peroxide

A dialdehyde–diboronate-functionalized tetraphenylethene (TPE-DABF) was reported as a H₂O₂-specific AIE luminogen.

Chemical approaches to discovery and study of sources and targets of hydrogen peroxide redox signaling through NADPH oxidase proteins

Hydrogen peroxide (H2O2) is a prime member of the reactive oxygen species (ROS) family of molecules produced during normal cell function and in response to various stimuli, but if left unchecked, it can inflict oxidative damage on all types of biological macromolecules and lead to cell death. In this context, a major source of H2O2 for redox signaling purposes is the NADPH oxidase (Nox) family of enzymes, which were classically studied for their roles in phagocytic immune response but have now been found to exist in virtually all mammalian cell types in various isoforms with distinct tissue and subcellular localizations. Downstream of this tightly regulated ROS generation, site-specific, reversible covalent modification of proteins, particularly oxidation of cysteine thiols to sulfenic acids, represents a prominent posttranslational modification akin to phosphorylation as an emerging molecular mechanism for transforming an oxidant signal into a dynamic biological response. We review two complementary types of chemical tools that enable (a) specific detection of H2O2 generated at its sources and (b) mapping of sulfenic acid posttranslational modification targets that mediate its signaling functions, which can be used to study this important chemical signal in biological systems.

A Dual Sensor for pH and Hydrogen Peroxide Using Polymer-Coated Optical Fibre Tips

This paper demonstrates the first single optical fibre tip probe for concurrent detection of both hydrogen peroxide (H₂O₂) concentration and pH of a solution. The sensor is constructed by embedding two fluorophores: carboxyperoxyfluor-1 (CPF1) and seminaphtharhodafluor-2 (SNARF2) within a polymer matrix located on the tip of the optical fibre. The functionalised fibre probe reproducibly measures pH, and is able to accurately detect H₂O₂ over a biologically relevant concentration range. This sensor offers potential for non-invasive detection of pH and H₂O₂ in biological environments using a single optical fibre.

Nonesterified Fatty Acid-Induced Endoplasmic Reticulum Stress in Cattle Cumulus Oocyte Complexes Alters Cell Metabolism and Developmental Competence

Reduced oocyte quality has been associated with poor fertility of high-performance dairy cows during peak lactation, due to negative energy balance. We examined the role of nonesterified fatty acids (NEFAs), known to accumulate within follicular fluid during under- and overnutrition scenarios, in causing endoplasmic reticulum (ER) stress of in vitro maturated cattle cumulus-oocyte complexes (COCs). NEFA concentrations were: palmitic acid (150 μM), oleic acid (200 μM), and steric acid (75 μM). Abattoir-derived COCs were randomly matured for 24 h in the presence of NEFAs and/or an ER stress inhibitor, salubrinal. Total and hatched blastocyst yields were negatively impacted by NEFA treatment compared with controls, but this was reversed by salubrinal. ER stress markers, activating transcription factor 4 (Atf4) and heat shock protein 5 (Hspa5), but not Atf6, were significantly up-regulated by NEFA treatment within whole COCs but reversed by coincubation with salubrinal. Likewise, glucose uptake and lactate production, measured in spent medium samples, showed a similar pattern, suggesting that cumulus cell metabolism is sensitive to NEFAs via an ER stress-mediated process. In contrast, while mitochondrial DNA copy number was recovered in NEFA-treated oocytes, oocyte autofluorescence of the respiratory chain cofactor, FAD, was lower following NEFA treatment of COCs, and this was not reversed by salubrinal, suggesting the negative impact was via reduced mitochondrial function. These results reveal the significance of NEFA-induced ER stress on bovine COC developmental competence, revealing a potential therapeutic target for improving oocyte quality during peak lactation.

Synthetic aminopyrrolic receptors have apoptosis inducing activity

We report two synthetic aminopyrrolic compounds that induce apoptotic cell death. These compounds have been previously shown to act as receptors for mannosides. The extent of receptor-induced cell death is greater in cells expressing a high level of high-mannose oligosaccharides than in cells producing lower levels of high-mannose glycans. The ability of synthetic receptors to induce cell death is attenuated in the presence of external mannosides. The present results provide support for the suggestion that the observed cell death reflects an ability of the receptors to bind mannose displayed on the cell surface. Signaling pathway studies indicate that the synthetic receptors of the present study promote JNK activation, induce Bax translocation to the mitochondria, and cause cytochrome c release from the mitochondria into the cytosol, thus promoting caspase-dependent apoptosis. Such effects are also observed in cells treated with mannose-binding ConA. The present results thus serve to highlight what may be an attractive new approach to triggering apoptosis via modes of action that differ from those normally used to promote apoptosis.

A Bioorthogonal Reaction of N-Oxide and Boron Reagents

The development of bioorthogonal reactions has classically focused on bond-forming ligation reactions. In this report, we seek to expand the functional repertoire of such transformations by introducing a new bond-cleaving reaction between N-oxide and boron reagents. The reaction features a large dynamic range of reactivity, showcasing second-order rate constants as high as 2.3×10(3)  M(-1)  s(-1) using diboron reaction partners. Diboron reagents display minimal cell toxicity at millimolar concentrations, penetrate cell membranes, and effectively reduce N-oxides inside mammalian cells. This new bioorthogonal process based on miniscule components is thus well-suited for activating molecules within cells under chemical control. Furthermore, we demonstrate that the metabolic diversity of nature enables the use of naturally occurring functional groups that display inherent biocompatibility alongside abiotic components for organism-specific applications.

Hydrogen peroxide-activatable antioxidant prodrug as a targeted therapeutic agent for ischemia-reperfusion injury

Overproduction of hydrogen peroxide (H₂O₂) causes oxidative stress and is the main culprit in the pathogenesis of ischemia/reperfusion (I/R) injury. Suppression of oxidative stress is therefore critical in the treatment of I/R injury. Here, we report H₂O₂-activatable antioxidant prodrug (BRAP) that is capable of specifically targeting the site of oxidative stress and exerting anti-inflammatory and anti-apoptotic activities. BRAP with a self-immolative boronic ester protecting group was designed to scavenge H₂O₂ and release HBA (p-hydroxybenzyl alcohol) with antioxidant and anti-inflammatory activities. BRAP exerted potent antioxidant and anti-inflammatory activity in lipopolysaccharide (LPS)- and H₂O₂-stimulated cells by suppressing the generation of ROS and pro-inflammatory cytokines. In mouse models of hepatic I/R and cardiac I/R, BRAP exerted potent antioxidant, anti-inflammatory and anti-apoptotic activities due to the synergistic effects of H₂O₂-scavenging boronic esters and therapeutic HBA. In addition, administration of high doses of BRAP daily for 7 days showed no renal or hepatic function abnormalities. Therefore BRAP has tremendous therapeutic potential as H₂O₂-activatable antioxidant prodrug for the treatment of I/R injuries.

Multifunctional self-assembled polymeric nanoprobes for FRET-based ratiometric detection of mitochondrial H2O2 in living cells

A ratiometric, multifunctional nanoprobe was prepared consisting of a self-assembled polymeric micelle as the carrier, tetraphenylethene (TPE) as the donor, fluorescent boronate as the H2O2-responsive acceptor, and triphenylphosphonium as a mitochondria-targeted moiety. The assembled nanoparticles could detect both exogenous and endogenous mitochondrial H2O2 changes in living cells.

Fluorescence Ratiometric Assay Strategy for Chemical Transmitter of Living Cells Using H2O2-Sensitive Conjugated Polymers

A new water-soluble conjugated poly(fluorene-co-phenylene) derivative (PFP-FB) modified with boronate-protected fluorescein (peroxyfluor-1) via PEG linker has been designed and synthesized. In the presence of H2O2, the peroxyfluor-1 group can transform into green fluorescent fluorescein by deprotecting the boronate protecting groups. In this case, upon selective excitation of PFP-FB backbone at 380 nm, efficient fluorescence resonance energy transfer (FRET) from PFP-FB backbone to fluorescein occurs, and accordingly, the fluorescence color of PFP-FB changes from blue to green. Furthermore, the emission color of PFP-FB and the FRET ratio change in a concentration-dependent manner. By taking advantage of PFP-FB, ratiometric detection of choline and acetylcholine (ACh) through cascade enzymatic reactions and further dynamic monitoring of the choline consumption process of cancer cells have been successfully realized. Thus, this new polymer probe promotes the development of enzymatic biosensors and provides a simpler and more effective way for detecting the chemical transmitter of living cells.

Selective Modification of Halloysite Nanotubes with 1-Pyrenylboronic Acid: A Novel Fluorescence Probe with Highly Selective and Sensitive Response to Hyperoxide

A novel fluorescence probe based on modified halloysite nanotubes (HNTs) by using 1-pyrenylboronic acid selectively grafted onto the inner surface of lumen was successfully achieved. The solid-state nuclear magnetic resonance ((13)C and (11)B), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) confirmed that the boronic acid group only binds to alumina at the tube lumen and does not bind the tube's outer siloxane surface. The modified HNTs (HNTs-PY) inherit the spectroscopic properties relating to the pyrene units. Interestingly, the established Al-O-B linkage gives the H2O2-sensitivity to pyrene grafted tubes. HNTs-PY exhibits a highly specific "turn-off" response for hyperoxide over other reactive oxygen species (ROS) and oxidative ions owing to their chemoselective boronate-to-phenol switch. The "turn-off" response can even be tracked when the additional amount of H2O2 was limited to 1 × 10(-6) mol. Thus, the selective modification method under mild conditions for the design of novel organic-inorganic hybrid fluorescence probe may open up a broader application as well as for identification and diagnosis.

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.