Rational design of fluorescein-based fluorescence probes. Mechanism-based design of a maximum fluorescence probe for singlet oxygen

Selective photoinactivation of protein function through environment-sensitive switching of singlet oxygen generation by photosensitizer

Chromophore-assisted light inactivation is a promising technique to inactivate selected proteins with high spatial and temporal resolution in living cells, but its use has been limited because of the lack of a methodology to prevent nonspecific photodamage in the cell owing to reactive oxygen species generated by the photosensitizer. Here we present a design strategy for photosensitizers with an environment-sensitive off/on switch for singlet oxygen ((1)O(2)) generation, which is switched on by binding to the target, to improve the specificity of protein photoinactivation. (1)O(2) generation in the unbound state is quenched by photoinduced electron transfer, whereas (1)O(2) generation can occur in the hydrophobic environment provided by the target protein, after specific binding. Inositol 1,4,5-trisphosphate receptor, which has been suggested to have a hydrophobic pocket around the ligand binding site, was specifically inactivated by an environment-sensitive photosensitizer-conjugated inositol 1,4,5-trisphosphate receptor ligand without (1)O(2) generation in the cytosol of the target cells, despite light illumination, demonstrating the potential of environment-sensitive photosensitizers to allow high-resolution control of generation of reactive oxygen species in the cell.

Swallow-tailed perylene derivative: a new tool for fluorescent imaging of lipid hydroperoxides

A swallow-tailed perylene derivative including a triphenylphosphine moiety was synthesized and applied to the detection and the live-cell imaging of lipid hydroperoxides. The novel probe, named Spy-LHP, reacted rapidly and quantitatively with lipid hydroperoxides to form the corresponding oxide, Spy-LHPOx, which emits extremely strong fluorescence (Phi approximately 1) in the visible range (lambda(em) = 535 nm, 574 nm). Spy-LHP was highly selective for lipid hydroperoxides, and the addition of other reactive oxygen species (ROS) including hydrogen peroxides, hydroxyl radical, superoxide anion, nitric oxide, peroxynitrite, and alkylperoxyl radical, caused no significant increase in the fluorescence intensity. The probe exhibited good localization to cellular membranes and was successfully applied to the confocal laser scanning microscopy (CLSM) imaging of lipid hydroperoxides in live J774A.1 cells, in which lipid peroxidation was proceeded by the stimulation of 2,2-azobis(2-amidinopropane)dihydrochloride (AAPH). These findings establish Spy-LHP as a promising new tool for investigating the physiology of lipid hydroperoxides.

Investigation of an Acid–Base and Redox Molecular Switch: From Bulk to the Single-Molecule Level

In this work we investigate a new fluorescent molecular switch based on the interconversion between the fluorescent zwitterionic form (ZW1) and the non-fluorescent anionic state (MC2) of a spirocyclic Meisenheimer complex of 1,3,5-trinitrobenzene. Density functional theory molecular orbital calculations reveal that photo-induced electron transfer from a guanidine group to the trinitrocyclohexadiene fluorophore of the complex quenches the emission from MC2. Protonation, as well as coordination of other Lewis acids to the guanidine group, suppress the quenching mechanism and allow the complex to fluoresce. In agreement with the calculations, reversible on-off fluorescence switching of the ZW1-MC2 bulk system occurs by protonation-deprotonation of the guanidine moiety upon acid-base addition. Interestingly, spectroelectrochemical ensemble measurements show that switching of the ZW1-MC2 pair can also be attained electrochemically, thus unraveling the versatile functioning of this system. The ultimate limit of monitoring the reversible on-off operation of individual switch molecules is reached by means of single-molecule fluorescence spectroscopy, which demonstrates the potential of the ZW1-MC2 system to be used as a true single-molecule switch on the nanometer scale.

Molecular switch based on a biologically important redox reaction

Building on our earlier report of a single-molecule probe, we show how biologically important redox centers, nicotinamide and quinone, incorporated into a fluorophore-spacer-receptor molecular structure, form redox active molecular switches, with the photoinduced electron-transfer behavior of each depending on the oxidation state of the receptor subunit. The switch based on nicotinamide (3/6) is strongly fluorescent in its oxidized state (Phi(F) approximately 1.0) but nonfluorescent in the reduced state (Phi(F) < 0.001) due to electron transfer from the reduced nicotinamide to the photoexcited fluorophore. The fluorescence can be reversibly switched off and on chemically by successive reduction with NaBH(3)CN and oxidation with tetrachlorobenzoquinone and switched electrochemically over 10 cycles without significant degradation. A similar switch based on quinonimine turned out to be nonfluorescent in both reduced and oxidized states: in addition to a similar quenching mechanism in the reduced state, quenching also occurs in the oxidized state, due to electron transfer from the fluorophore to the receptor. Ab initio quantum chemical calculations of orbital energy levels were used to corroborate these quenching mechanisms. Calculations predicted photoinduced electron transfer to be energetically favorable in all cases where quenching was observed and unfavorable in all cases where it was not. Application of the perylene analogue as a biosensor has also been demonstrated by coupling the switch to the catalytic pathway of yeast alcohol dehydrogenase, a common NADH/NAD(+)-utilizing enzyme.

Study of Singlet Oxygen Equilibrium in Dioctadecyldimethylammonium Chloride Vesicles Employing 2-(n-(N,N,N-trimethylamine)-n-alkyl)- 5-alkylfuryl Halides†

Steady state photolysis and time resolved near infrared luminescence detection were employed to study the reaction kinetics of singlet oxygen with three different lipid-soluble probes incorporated in large unilamellar dioctadecyldimethylammonium chloride (DODAC) vesicles. The probes: 2-(4-(N,N,N-trimethylamine)-butyl)-5-dodecylfuryl bromide (DFTA), 2-(12-(N,N,N-trimethylamine)-dodecyl)-5-hexylfuryl bromide (HFDA) and 2-(1-(N,N,N-trimethylamine)-methyl)-5-methylfuryl iodide (MFMA) are useful in studying both singlet oxygen dynamics and its equilibrium in microcompartmentalized systems because they are actinometers in lipidic microphases. These probes contain a reactive furan ring, which will be located at different depths in the bilayer of DODAC vesicles. In the limit of the approximations, the result indicates an inhomogeneous equilibrium distribution of singlet oxygen across the bilayer. The calculated mean partitioning constant of singlet oxygen equals 2.8 and 8.3 at 20 degrees C and 40 degrees C, respectively, in the order of the previously reported constants for other microorganized systems such as sodium dodecylsulfate and cetyltrimethylammonium halide micelles and water/oil microemulsions.

An enzymatically activated fluorescence probe for targeted tumor imaging

Beta-galactosidase is a widely used reporter enzyme, but although several substrates are available for in vitro detection, its application for in vivo optical imaging remains a challenge. To obtain a probe suitable for in vivo use, we modified our previously developed activatable fluorescence probe, TG-betaGal (J. Am. Chem. Soc. 2005, 127, 4888-4894), on the basis of photochemical and photophysical experiments. The new probe, AM-TG-betaGal, provides a dramatic fluorescence enhancement upon reaction with beta-galactosidase, and further hydrolysis of the ester moiety by ubiquitous intracellular esterases affords a hydrophilic product that is well retained within the cells without loss of fluorescence. We used a mouse tumor model to assess the practical utility of AM-TG-betaGal, after confirming that tumors in the model could be labeled with an avidin-beta-galactosidase conjugate. This conjugate was administered to the mice in vivo, followed by AM-TG-betaGal, and subsequent ex vivo fluorescence imaging clearly visualized intraperitoneal tumors as small as 200 microm. This strategy has potential clinical application, for example, in video-assisted laparoscopic tumor resection.

New noncellular fluorescence microplate screening assay for scavenging activity against singlet oxygen

In the present study, a new fluorescence microplate screening assay for evaluating scavenging activity against singlet oxygen (1O2) was implemented. The chemical generation of 1O2 was promoted using the thermodissociable endoperoxide of disodium 3,3'-(1,4-naphthalene)bispropionate (NDPO2). The detection of 1O2 was achieved using dihydrorhodamine 123 (DHR), a nonfluorescent molecule that is oxidizable to the fluorescent form rhodamine 123 (RH). The combined use of a 1O2-selective generator and a highly sensitive probe (DHR) was then successfully applied to perform a screening assay of the 1O2 scavenging activities of ascorbic acid, penicillamine, cysteine, N-acetylcysteine (NAC), methionine, reduced glutathione (GSH), dihydrolipoic acid, lipoic acid, and sodium azide. All of these antioxidants exhibited concentration-dependent 1O2 scavenging capacities. They could be ranked according to observed activity: ascorbic acid>cysteine>penicillamine>dihydrolipoic acid>GSH>NAC>sodium azide>lipoic acid (IC50 values of 3.0+/-0.2, 8.0+/-0.7, 10.9+/-0.8, 25.2+/-4.5, 57.4+/-5.9, 138+/-13, 1124+/-128, 2775+/-359 microM, mean+/-SEM, respectively)>methionine (35% of scavenging effect at 10 mM). In conclusion, the use of NDPO2 as a selective generator for 1O2 and its fluorescence detection by the highly sensitive probe DHR is shown to be a reliable and resourceful analytical alternative means to implement a microplate screening assay for scavenging activity against 1O2.

[Development and biological applications of various bioimaging probes]

Fluorescence imaging is the most powerful technique currently available for continuous observation of dynamic intracellular processes in living cells. However, only a very limited range of biomolecules can be visualized because of the lack of flexible design strategies for fluorescence probes. In our laboratory, it was elucidated that fluorescein which has been widely employed as a core of fluorescence probes could be understood as a directly linked electron donor/fluorophore acceptor system. Fluorescence properties of fluorescein derivatives could be easily anticipated and modulated by controlling the rate of photoinduced electron transfer (PeT) from the donor moiety to the xanthene fluorophore. Further, we found that the opposite direction of PeT from the singlet excited fluorophore to the electron acceptor moiety could be occurred. More than twenty probes for imaging of nitric oxide, beta-galactosidase, highly reactive oxygen species, zinc ion et al. have been developed according to precise and rational design strategies based on PeT mechanism.

Tunable design strategy for fluorescence probes based on 4-substituted BODIPY chromophore: improvement of highly sensitive fluorescence probe for nitric oxide

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is a well-known fluorophore, with a high molar extinction coefficient and high fluorescence quantum efficiency (Phi(fl)). Furthermore, its structure can be modified to change its excitation and emission wavelengths. However, little work has been done on the structural modification of fluorines at the B-4 position with other functional groups. We synthesized 4-methoxy-substituted BODIPY derivatives in satisfactory yields, and found that they exhibited improved solubility in aqueous solution. Moreover, their oxidation and reduction potentials were greatly decreased without any change in their absorbance and fluorescence properties. These features of 4-substituted BODIPYs may be useful for developing novel fluorescence probes based on the intramolecular photoinduced electron transfer (PeT) mechanism, because it is possible to optimize the PeT process precisely by modulating the electrochemical properties of the fluorophore. The value of this approach is exemplified by its application to the development of a highly sensitive and pH-independent fluorescence probe for nitric oxide.

A new chemiluminescence probe for singlet oxygen based on tetrathiafulvalene-anthracene dyad capable of performing detection in water/alcohol solution

A new tetrathiafulvalene-anthracene dyad 1 with two "tetraethylene glycol" units was synthesized and characterized. Strong chemiluminescence was observed upon reaction of dyad 1 with singlet oxygen (1O2), and this reaction shows fairly good selectivity toward 1O2 over other reactive oxygen species. Due to the introduction of two hydrophilic "tetraethylene glycol" units, the detection of 1O2 with dyad 1 can be performed in alcohol/water solution, which is relatively a mild medium when compared with water/tetrahydrofuran solution required by other tetrathiafulvalene-anthracene dyads. Dyad 1 may have a wider use for detection of 1O2 in biological systems.

Recent advances in fluorescent probes for the detection of reactive oxygen species

Reactive oxygen species (ROS) have captured the interest of many researchers in the chemical, biological, and medical fields since they are thought to be associated with various pathological conditions. Fluorescent probes for the detection of ROS are promising tools with which to enhance our understanding of the physiological roles of ROS, because they provide spatial and temporal information about target biomolecules in in vivo cellular systems. ROS probes, designed to detect specific ROS with a high selectivity, would be desirable, since it is now becoming clear that each ROS has its own unique physiological activity. However, dihydro-compounds such as 2',7'-dichlorodihydrofluorescein (DCFH), which have traditionally been used for detecting ROS, tend to react with a wide variety of ROS and are not completely photostable. Some attractive fluorescent probes that exhibit a high degree of selectivity toward specific ROS have recently been reported, and these selective probes are expected to have great potential for elucidating unknown physiological mechanisms associated with their target ROS. This review focuses on the design, detection mechanism, and performance of fluorescent probes for the detection of singlet oxygen ((1)O(2)), hydrogen peroxide (H(2)O(2)), hydroxyl radicals ((.)OH), or superoxide anion (O(2) (-.)), a field in which remarkable progress has been achieved in the last few years.

A new terbium(III) chelate as an efficient singlet oxygen fluorescence probe

A terbium(III) chelate fluorescence probe for detection of singlet oxygen (1O2) in aqueous media, N,N,N1,N1-[2,6-bis(3'-aminomethyl-1'-pyrazolyl)-4-(9''-anthryl)pyridine] tetrakis (acetate)-Tb3+ (PATA-Tb3+), was designed and synthesized. The new chelate is highly water soluble, is almost nonfluorescent, and can specifically react with 1O2 to yield a strongly fluorescent chelate, the endoperoxide of PATA-Tb3+, accompanied by a remarkable increase in the fluorescence quantum yield from 0.46 to 10.5%. The long fluorescence lifetime of the endoperoxide (2.76 ms) allows the probe to be used favorably for time-resolved fluorescence detection of 1O2. The studies of fluorescence property and reaction specificity indicate that the new probe is highly sensitive and selective for 1O2. The probe was used for quantitative detection of 1O2 generated from a MoO4(2-) -H2O2 system to give a detection limit of 10.8 nM. In addition, the good applicability of the probe was demonstrated by the real-time monitoring of the kinetic process of 1O2 generation in a horseradish peroxidase-catalyzed oxidation system of indole-3-acetic acid in a weakly acidic buffer.

Determination of H2O2-dependent generation of singlet oxygen from human saliva with a novel chemiluminescence probe

Singlet oxygen (1O2) has been shown to play an important role in salivary defense system, but its generation process and level from human saliva remain uncertain due to the lack of a reliable detection method. We have previously reported 4,4'(5')-bis[2-(9-anthryloxy)ethylthio]tetrathiafulvalene (BAET) as a novel chemiluminescence probe for 1O2. In this work, the probe is successfully used to characterize H2O2-dependent generation of 1O2 from saliva in real time. However, the yield of 1O2 is found to be very low, for example, being about 0.13 nmol from 200 microL saliva in the presence of 1 mM of hydrogen peroxide over a 5-s reaction period. The result is also compared with that obtained with another 1O2 probe 2-methyl-6-phenyl-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (CLA), demonstrating that, besides 1O2, the other reactive oxygen species such as hydroxyl radical may also be involved in the reaction of saliva with H2O2. Furthermore, the present study shows that the selectivity of BAET for 1O2 is much higher than that of CLA and thus BAET is highly suited for the detection of 1O2 in the presence of other reactive oxygen species in biological systems.

Time-Resolved Detection of Hot Electron-Induced Electrochemiluminescence of Fluorescein in Aqueous Solution

Strong electrogenerated chemiluminescence (ECL) of fluorescein is generated during cathodic pulse polarization of oxide-covered aluminum electrodes and the resulting decay of emission is so sluggish that time-resolved detection of fluorescein is feasible. The present ECL in aqueous solution is based on the tunnel emission of hot electrons into the aqueous electrolyte solution, which probably results in the generation of hydrated electrons and hydroxyl radicals acting as redox mediators. The successive one-electron redox steps with the primary radicals result in fluorescein in its lowest excited singlet state. The method allows the detection of fluorescein (or its derivatives containing usable linking groups to biomolecules) over several orders of magnitude of concentration with detection limits well below nanomolar concentration level. The detection limits can still be lowered, e.g., by addition of azide or bromide ions as coreactants. The results suggest that the derivatives of fluorescein, such as fluorescein isothiocyanate (FITC), can be detected by time-resolved measurements and thus be efficiently used as electrochemiluminescent labels in bioaffinity assays.

Use of Fluorescence Probes for Detection of Reactive Nitrogen Species: A Review

The biological and toxicological effects that have been attributed to reactive nitrogen species (RNS) are increasingly stirring the scientific inquisitiveness about the molecular mechanisms involved. However, RNS present some characteristics that complicate their detection, namely their short lifetime and the normal presence of a variety of endogenous compounds capable of reacting with these reactive species, when the studies are performed in biological matrices. The development of methodologies capable of circumvent these difficulties is thus of fundamental importance. Fluorescence probes are particularly important due to their high sensibility and usefulness in temporal and spatial monitoring of RNS, particularly in microanalysis conditions in biological media akin to cells or tissues. In the present review is given an account of the fluorescence probes that have been used for detection of nitric oxide (*NO), peroxynitrite anion (ONOO-), as well as of some of its derivatives in biological and nonbiological media.

Optical detection of singlet oxygen from single cells

The lowest excited electronic state of molecular oxygen, singlet molecular oxygen, O(2)(a (1)Delta(g)), is a reactive species involved in many chemical and biological processes. To better understand the roles played by singlet oxygen in biological systems, particularly at the sub-cellular level, optical tools have been developed to create and directly detect this transient state in time- and spatially-resolved experiments from single cells. Data obtained indicate that, contrary to common perception, this reactive species can be quite long-lived in a cell and, as such, can diffuse over appreciable distances including across the cell membrane into the extracellular environment. On one hand, these results demonstrate that the behavior of singlet oxygen in an intact cell can be significantly different from that inferred from model bulk studies. More generally, these results provide a new perspective for mechanistic studies of intra- and inter-cellular signaling and events that ultimately lead to photo-induced cell death.

On-Bead Fluorescence Assay for Serine/Threonine Kinases

[chemical reaction: see text]. A novel fluorescence-based assay for serine/threonine kinases is described. Base-mediated beta-elimination of the phosphate moiety and the Michael addition of a thiol-containing fluorescent molecule allows convenient and efficient detection of the enzyme activity. This approach may be broadly applicable to various serine/threonine kinases.

Fluorescence probes used for detection of reactive oxygen species

Endogenously produced pro-oxidant reactive species are essential to life, being involved in several biological functions. However, when overproduced (e.g. due to exogenous stimulation), or when the levels of antioxidants become severely depleted, these reactive species become highly harmful, causing oxidative stress through the oxidation of biomolecules, leading to cellular damage that may become irreversible and cause cell death. The scientific research in the field of reactive oxygen species (ROS) associated biological functions and/or deleterious effects is continuously requiring new sensitive and specific tools in order to enable a deeper insight on its action mechanisms. However, reactive species present some characteristics that make them difficult to detect, namely their very short lifetime and the variety of antioxidants existing in vivo, capable of capturing these reactive species. It is, therefore, essential to develop methodologies capable of overcoming this type of obstacles. Fluorescent probes are excellent sensors of ROS due to their high sensitivity, simplicity in data collection, and high spatial resolution in microscopic imaging techniques. Hence, the main goal of the present paper is to review the fluorescence methodologies that have been used for detecting ROS in biological and non-biological media.

Essential role of singlet oxygen species in cytochrome P450-dependent substrate oxygenation by rat liver microsomes

Previously, we reported that singlet oxygen (1O2) was involved in rat liver microsomal P450-dependent substrate oxygenations in such reactions as p-hydroxylation of aniline, O-deethylation of 7-ethoxycoumarin, omega- and (omega-1)-hydroxylations of lauric acid, O-demethylation of p-nitroanisole, and N-demethylation of aminopyrine. In order to confirm the generality of 1O2 involvement, we have further investigated which kinds of reactive oxygen species (ROS) are formed during P450-dependent substrate oxygenation in microsomes. We examined CYP2E1-dependent hydroxylation of p-nitrophenol in rat liver microsomes in the presence of some ROS scavengers, because CYP2E1 has been reported to predominantly generate ROS in the hepatic microsomes and to relate with the oxidative stress in the body. The addition of 1O2 quenchers, beta-carotene, suppressed the hydroxylation of p-nitrophenol. Furthermore, a nonspecific P450 inhibitor, SKF525A, and a ferric chelator, deferoxamine, both suppressed the hydroxylation. No other ROS scavengers such as superoxide dismutase (SOD), catalase, or mannitol altered the reaction. 1O2 was detectable during the reaction in the microsomes as measured by an electron spin resonance (ESR) spin-trapping method when 2,2,6,6-tetramethyl-4-piperidone (TMPD) was used as a spin-trapping reagent. The 1O2 was quenched by additions of beta-carotene, p-nitrophenol, and SKF525A. The reactivity of p-nitrophenol and 1O2 correlated linearly with its hydroxylation rate in the microsomes. On the basis of these results, we conclude that 1O2 contributes to the p-nitrophenol hydroxylation in rat liver microsomes, by adding a new example of 1O2 involvement in the CYP2E1-dependent substrate oxygenations.

A new protein conformation indicator based on biarsenical fluorescein with an extended benzoic acid moiety

We demonstrate herein a new protein conformation indicator based on biarsenical fluorescein with an extended benzoic acid moiety. The present indicator is reactive to a genetically introduced tetracysteine motif (Cys-Cys-Xaa-Xaa-Cys-Cys, where Xaa is a noncysteine amino acid) of proteins. Compared to the original biarsenical fluorescein (FlAsH) and the biarsenical Nile red analogue (BArNile), the present indicator exhibited larger fluorescence intensity changes in response to Ca(2+)-induced conformational rearrangements of calmodulin. A calculation of the highest occupied molecular orbital (HOMO) level of the benzoic acid moiety of the indicator molecule supports possible involvement of a photoinduced electron transfer (PET) process. These results indicate that the present indicator is useful for sensitive detection of protein conformational changes.

Design and development of a fluorescent probe for monitoring hydrogen peroxide using photoinduced electron transfer

A novel fluorescent probe, 7-hydroxy-2-oxo-N-(2-(diphenylphosphino)ethyl)-2H-chromene-3-carboxamide (DPPEA-HC) was developed for use in monitoring hydrogen peroxide (H2O2) production. DPPEA-HC, which consists of a diphenylphosphine moiety and a 7-hydroxycoumarin moiety, reacts with H2O2 to form DPPEA-HC oxide, which is analogous to the reaction of triphenylphosphine with hydroperoxides such as H2O2 to form triphenylphosphine oxide. Photoinduced electron transfer (PET) was applied in the design of DPPEA-HC. Since the diphenylphosphine moiety and the 7-hydroxycoumarin moiety would act as the PET donor and the acceptor, respectively, it would be expected that DPPEA-HC would rationally cancel the PET process via the formation of DPPEA-HC oxide, based on the calculated energy levels of the donor and the acceptor moieties using the B3LYP/6-31G*//AM1 method. The fluorescence intensity of DPPEA-HC increased on the addition of a H2O2 solution in 100 mM sodium phosphate buffer (pH7.4), as predicted from the energy level calculation and a good correlation between increase in the fluorescence of DPPEA-HC and the concentration of H2O2 was observed. DPPEA-HC was also fluoresced by H2O2, which was enzymatically produced in xanthine/xanthine oxidase/superoxide dismutase (XA/XOD/SOD) system. The increase in the fluorescence of DPPEA-HC in the presence of H2O2 immediately ceased on the addition of catalase (CAT), which catalyzes the disproportionation of H2O2. In addition, DPPEA-HC was found to have a much higher selectivity for H2O2 and a greater resistance to autoxidation than 2',7'-dichlorodihydrofluoresein (DCFH). Time-resolved fluorescence measurements of DPPEA-HC and DPPEA-HC oxide confirmed that the fluorescence off/on switching mechanism of DPPEA-HC is based on the PET on/off control.

Ratiometric Singlet Oxygen Nano-optodes and Their Use for Monitoring Photodynamic Therapy Nanoplatforms

Ratiometric photonic explorers for bioanalysis with biologically localized embedding (PEBBLE) nanoprobes have been developed for singlet oxygen, using organically modified silicate (ORMOSIL) nanoparticles as the matrix. A crucial aspect of these ratiometric singlet-oxygen fluorescent probes is their minute size. The ORMOSIL nanoparticles are prepared via a sol-gel-based process and the average diameter of the resultant particles is about 160 nm. These sensors incorporate the singlet-oxygen-sensitive 9,10-dimethyl anthracene as an indicator dye and a singlet-oxygen-insensitive dye, octaethylporphine, as a reference dye for ratiometric fluorescence-based analysis. We have found experimentally that these nanoprobes have much better sensitivity than does the conventional singlet-oxygen-free dye probe, anthracene-9,10-dipropionic acid disodium salt. The much longer lifetime of singlet oxygen in the ORMOSIL matrix, compared to aqueous solutions, in addition to the relatively high singlet oxygen solubility because of the highly permeable structure and the hydrophobic nature of the outer shell of the ORMOSIL nanoparticles, results in an excellent overall response to singlet oxygen. These nanoprobes have been used to monitor the singlet oxygen produced by "dynamic nanoplatforms" that were developed for photodynamic therapy. The singlet oxygen nanoprobes could potentially be used to quantify the singlet oxygen produced by macrophages.

A new europium chelate-based phosphorescence probe specific for singlet oxygen

The first Eu3+ chelate-based phosphorescence probe specific for singlet oxygen has been designed, synthesized and characterized. The probe is highly sensitive, selective and water soluble for time-resolved luminescence detection of singlet oxygen with a detection limit of 2.8 nM.

Improvement of Fluorescence Characteristics of Coumarins: Syntheses and Fluorescence Properties of 6-Methoxycoumarin and Benzocoumarin Derivatives as Novel Fluorophores Emitting in the Longer Wavelength Region and Their Application to Analytical Reagents

To improve the fluorescence characteristics, especially emission wavelength, of coumarins, various 3-substituted-6-methoxycoumarin derivatives were synthesized, and then benzocoumarin derivatives were also synthesized in expectation of the shift to the longer wavelength region by the extension of the conjugated system. Their fluorescence properties were investigated spectrophotometrically in acetonitrile and evaluated from the viewpoint of the intramolecular charge transfer (ICT) between push- and pull-substituents in the ground and the excited states. Among them, benzocoumarin derivatives especially fluoresced in the longer wavelength around 540 nm with remarkably large Stokes shifts beyond 10,000 cm(-1). Using such fluorophores, some novel fluorescence derivatization reagents for carboxylic acids, alcohols, phenols, and amines were preliminarily prepared as an example, and their derivatized products were also found to fluoresce in the longer wavelength region with large Stokes shifts.

A selective and sensitive chemiluminescence reaction of 4,4′(5′)-bis[2-(9-anthryloxy)ethylthio]tetrathiafulvalene with singlet oxygen

4,4'(5')-Bis[2-(9-anthryloxy)ethylthio]tetrathiafulvalene bearing an electron-rich tetrathiafulvalene unit and a luminophore of anthracene shows a highly selective and sensitive chemiluminescence response to singlet oxygen.

A Novel Fluorescent Probe for Zinc Ion Based on Boron Dipyrromethene (BODIPY) Chromophore

ZnAB has the combined structure of N,N-bis(2-pyridylmethyl)ethylenediamine as a specific chelater for Zn(2+) and 1,3,5,7-tetramethyl-8-phenyl-boron dipyrromethene as a fluorophore. Complexation of ZnAB with Zn(2+) produces a remarkable enhancement of fluorescence intensity. ZnAB has the advantages of less sensitivity to solvent polarity and pH than fluorescein-based Zn(2+) probes. Furthermore, it is not influenced by other cations, such as Na(+), K(+), Ca(2+), and Mg(2+), which exist at high concentrations under physiological conditions, even at 2.5 mM. The results show that ZnAB is a Zn(2+) probe suitable for biological applications.