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To discriminate hydrogen sulfide (H2S) from thiol nucleophiles with similar reactivity is always a major challenge in developing new detection methods. In this paper, we report a colorimetric and ratiometric fluorescence probe selectively reactive to H2S, which was synthesized by hybridizing the fluorescent nitro-benz-2-oxa-1,3-diazole (NBD)-based derivative P-NBD with carbon dots (CDs). The selective reaction can be monitored by distinct ratiometric fluorescence or colorimetric variation. The nanohybrid probe exhibited two fluorescence bands centered at 440 nm and 543 nm, respectively. The yellow fluorescence at 543 nm from P-NBD is quenched by H2S, while the blue fluorescence is enhanced by weakening of the Forster resonance energy transfer (FRET) mechanism. It was observed that the apparent fluorescence color evolved from yellow to blue when exposed to different amounts of H2S, accompanied by the color change of the probe solution from yellow to red under natural light. The detection limit was estimated to be 57 nM in aqueous solution. We successfully applied this probe for the detection of H2S in real water samples, suggesting its potential application in environmental monitoring and protection.

Cuprous ion is an essential element for human life activities. However, excessive cuprous can cause dysfunction of the human body system. To help explain this evolving biology, we report a fluorescent probe for detecting unstable Cu(I). Cu(I) undergoes a metal complexation reaction with the sulfur element in the probe, resulting in a photoelectron transfer (PET) effect. The probe fluorescence is greatly suppressed, and rapid and selective visual detection of Cu(I) in the inorganic environment is realized. There is also a good linear relationship between the probe fluorescence intensity and the Cu(I) concentration (R

As new luminescent nanomaterials, carbon dots have superior properties regarding their multi-color emission, chemical stability and biocompatibility, which are important for potential biological and medicine applications. Tuning the photoluminescence of carbon dots using hydroxyl radical through fast chemical reaction can be a simple and cost-effective method to modify their optical properties. Carbon dots of red fluorescence (r-CDs) were first prepared from phenylenediamines by a solvothermal method and subsequently treated with hydroxyl radicals or tert-butyl peroxyl radicals to generate carbon dots with new emission properties. Instead, other reactive oxygen such as singlet oxygen and hypochlorite could mainly quench the fluorescence of the r-CDs. With further investigation, it was found that these oxygen radicals played roles like chemical scissors cutting the surface chain groups of r-CDs to smaller-sized CDs, resulting in blueshift of emission. These findings may be helpful to investigate the mechanism relating to fluorescence properties of carbon dots, and it also provides a new method to control the emission of carbon dots through simple chemical treatment.

Nitrogen doped carbon spheres with wrinkled cages (NCSWCs), which were used for the first time as metal-free catalysts, exhibited high catalytic activity and selectivity in the oxidation of 5-hydroxymethylfurfural (HMF) to 5-formyl-2-furancarboxylic acid (FFCA) under base-free conditions using tert-butyl hydroperoxide (TBHP) as the oxidant. The mechanistic studies found that this reaction was catalyzed by the synergy between NCSWCs and TBHP. The density functional theory (DFT) calculations further suggested that the hydroperoxyl radicals from TBHP adsorbed on the carbon atoms adjacent to the graphitic N atoms are the active sites.

Two-dimensional (2D) bismuth-based semiconductors have aroused intensive concern owing to their prominent photocatalytic activity for organic pollutants removal. In this work, a facile strategy for introducing oxygen vacancy in Bi-based oxyiodides (BixOyIz) sheet-like architectures to activate molecular oxygen was proposed. The structure, photoelectric properties and visible light (λ > 420 nm) induced photocatalytic activities of these samples for decomposition of bisphenol A (BPA) were systematically characterized and evaluated. The as-prepared Bi7O9I3 with a feeding Bi/I molar ratio of 1:1 exhibited the best photocatalytic activity comparable to those of similarly synthesized Bi7O9I3 with other molar ratios and BiOIO3 catalysts. The optimal Bi7O9I3 achieved excellent photocatalytic activity with 99.6 % degradation efficiency of BPA within 20 min and superior structural stability with 95.1 % degradation retention over 5 cycling tests. In addition, the resulting Bi7O9I3 sample displayed a high mineralization efficiency of BPA. Importantly, the plenty of oxygen vacancies (Vos) exsiting in Bi7O9I3 played the dominant role in both accelerating electron transfer and activating molecular oxygen to facilitate the generation of superoxide radical (O2·-) and singlet oxygen (1O2), thereby proceeding oxidative degradation of BPA molecules during photoreactions. The efforts and attempts are also extendable to synthesis other 2D photocatalysts, providing potential for effective charge-carrier separation and molecular oxygen activation.

Fluorescent quantum dots (QDs) of carbon and semiconductors have superior optical properties and show great potential in sensing applications. This paper reports a novel method for rapid detection of uranyl ions via ratiometric fluorescence signals by employing two types of QDs as the key materials. As the most soluble and stable toxic uranium species, uranyl has been recognized as an important index for nuclear industrial wastewater. However, its on-site, rapid, and sensitive determination remains challenging. This work uses the ratiometric fluorescent signal of QDs and combines a smartphone-based handheld device for on-site and rapid detection of uranyl. The ratiometric fluorescent probe is achieved by integrating carbon dots (C-dots) and CdTe QDs (MPA@CdTe QDs) through chemical hybridization. The presence of uranyl ions greatly quenches the red fluorescence of the CdTe QDs, whereas the green fluorescence keeps constant, leading to an obvious color change. An app and a 3D-printed accessory have been developed on a smartphone to analyze and calculate the content of uranyl on the basis of captured fluorescence signals from a test strip with an immobilized probe. This new designed mobile detection system displays good analytical performance for uranyl ions in a wide concentration range of 1 to 150 μM, which shows a great potential application in controlling the nuclear industrial pollution.

This paper reported a dual-mode probe for D-penicillamine on the basis of pH-mediated gold nanoparticles aggregation and fluorescence resonance energy transfer (FRET) from carbon dots. D-penicillamine is a zwitterionic compound and has different forms depending on specific pH ranges. The thiol group of D-penicillamine has high affinity towards the surface of gold nanoparticles and can replace other surface ligands. When pH values were close to its isoelectrical point (pH(I)), the D-penicillamine capped gold nanoparticles aggregated through hydrogen bonding or electrostatic interactions, resulting in the releasing of carbon dots from gold nanoparticles. The dual-mode probe consisted of fluorescent carbon dots and gold nanoparticles, and the fluorescence of carbon dots was quenched by the attached gold nanoparticles due to the FRET. Then, the fluorescence can be recovered in presence of D-penicillamine due to the gold nanoparticles aggregation in specific pH range. Under the optimum conditions, the probe has linear response for D-penicillamine in the 0.25-1.5 μM concentration range with a detection limit of 0.085 μM. This method provides a potential application in sensitive detection of D-penicillamine.

Singlet oxygen plays an important role in cancer chemotherapy and biology of reactive oxygen species. In recent years, there are some reports of selective fluorescent probes for detection and imaging of singlet oxygen but the existing probes have some major drawbacks including complicated synthetic routes, poor fluorescence enhancement effects. We report herein that anthracenylmethyl modified non-fluorescent derivatives of fluorescein and rhodamine-6G can reacts with 1O2, which resulted in C C bond cleavage that detach anthracene unit from the fluorophores resulting in strong fluorescence enhancement. These probes exhibit high selectivity and sensitivity in detection and imaging of 1O2 in chemical and in living cells. Our approach makes it simple and flexible for development of reaction-based 1O2 fluorescent probes for broad application in chemical, biomedical, and environmental sciences.

Ozone is widely used in air sterilization, food and medical disinfection in modern society, but high ozone levels in the living environment are considered harmful and have been associated with various respiratory diseases. Therefore, quick detection for ozone of part per million (ppm) levels is significant for living environment and an excited-state intramolecular proton transfer (ESIPT) compound has been synthesized. Due to an intrinsic excited-state intramolecular proton transfer (ESIPT) process, this “off-on” probe can fluoresce in the solid-state. This intrinsic fluorescent property makes it easy to detect lower concentration of ozone since the reaction product of probe can avoid being affected by pH and solubility through luminescence in the solid-state. The limit of gaseous ozone detection can be as low as 0.28 ppm for obviously distinguishable fluorescence colour from blue to cyan, showing that the probe can be useful for detecting ozone without the need of elaborate equipment.

Superoxide anion (O2•−) is one of the most important reactive oxygen species and its sensitive detection is of great significance and challenging in the field of environmental and hazardous chemicals monitoring. Herein, we report an off-on fluorescent probe based on ferric functionalized carbon dots (CDs) which were synthesized using p-phenylenediamine as starting material for the detection of O2•−. The initial green fluorescence of CDs was greatly quenched by Fe3+ based on energy transfer effect on account of the selective formation of ferric complex on the surface of CDs, but not by other metal ions. Interestingly, the fluorescence of CDs could be readily and selectively recovered upon the addition of O2•−, which can be used for the senstivie detection of superoxide. This type of off-on probe exhibited good photostability and high selectivity toward O2•− among other interfering substances including metal ions, reactive oxygen species as well as reductant substances. The probe showed good linearity with the concentration of O2•−, and the limit of detection for O2•− was estimated down to 25 pM in aqueous solution. Moreover, a paper based sensor for O2•− was fabricated with a visual detection limit as low as 4.4 nM, demonstrating a promising application for practical detection of superoxide anion.

The sensitive and selective analytical methods for real-time monitoring of sulfur dioxide and its derivatives are significant for human health, pollution-control and food safety. Herein, we report a new nanocomposite (Hex-FGO-DPS) consisting of cyanine dye and fluorescent graphene oxide with unique reactive properties for ratiometric fluorescent detection of bisulfite. The ratiometric fluorescence of Hex-FGO-DPS in aqueous solution can be sensitively, selectively and efficiently tuned by bisulfite through a specific nucleophilic addition reaction. In the presence of bisulfite, the ratiometric fluorescence intensity of Hex-FGO-DPS (F 470nm /F 580nm ) changes up to 25 folds, accompanied by a distinct color change from yellow to blue which can be visually identified. The detection limit was measured to be 0.44 μM. The probe can be further applied for sensing intracellular bisulfite through the ratiometric fluorescence imaging analysis in living cells. In addition, the probe Hex-FGO-DPS also can be used for selective determination of gaseous sulfur dioxide in atmosphere and aqueous solution. The simple, sensitive and effective strategy reported here could facilitate the development of portable and reliable sensor for visual identification applications.

The sensitive and selective fluorescence probe for hydroxyl radical analysis is of significance because hydroxyl radical plays key roles in many physiological and pathological processes. In this work, a novel organic fluorescence molecular probe OHP for hydroxyl radical is synthesized by a two-step route. The probe employs 4-bora-3a,4a-diaza-s-indacene (difluoroboron dipyrromethene, BODIPY) as the fluorophore and possesses relatively high fluorescence quantum yields (77.14%). Hydroxyl radical can rapidly react with the probe and quench the fluorescence in a good linear relationship (R2=0.9967). The limit of detection is determined to be as low as 11 nM. In addition, it has been demonstrated that the probe has a good stability against pH and light illumination, low cytotoxicity and high biocompatibility. Cell culture experimental results show that the probe OHP is sensitive and selective for imaging and tracking endogenous hydroxyl radical in live cells.

Hydrogen sulfide (H2S) is a biologically relevant molecule that has been newly identified as a gasotransmitter and is also a toxic gaseous pollutant. In this study, we report on a metal complex fluorescent probe to achieve the sensitive detection of H2S in a fluorescent “turn-on” mode. The probe bears a dansyl fluorophore with multidentate ligands for coordination with copper ions. The fluorescent “turn-on” mode is facilitated by the strong bonding between H2S and the Cu(II) ions to form insoluble copper sulfide, which leads to the release of a strongly fluorescent product. The H2S limit of detection (LOD) for the proposed probe is estimated to be 11 nM in the aqueous solution, and the utilization of the probe is demonstrated for detecting H2S in actual lake and mineral water samples with good reproducibility. Furthermore, we designed detector vials and presented their successful application for the visual detection of gaseous H2S.

An improved synthesis of dimethylhomoecoerdianthrone (HOCD), a dye used for singlet oxygen detection, was reported by isolation of a key intermediate followed by cyclization reaction. Moreover, dehydrogenative amination reaction between HOCD and alkyl amines and diamines resulted in amine functionalized HOCD derivatives with good yield. The observed reactivity depends on the nucleophilicity of amine and electrophilicity of HOCD. DFT calculations suggest that the reaction involves 1,4-Michael addition followed by migration of hydrogen atom due to aromatization. Under the aerated conditions, dehydrogenation occurs to restore the ketone structure. This C-N coupling reaction can be utilized to construct molecular materials with near infrared photonic properties. Finally, we illustrated that the HOCD derives, HOCD-SO3−, can be grafted to semiconductor nanocrystals (quantum dots) to give turn-on fluorescent nanoprobe for highly selective detection of singlet oxygen.

This work reports a novel dual-emissive fluorescent probe based on dye hybrid silica nanoparticles for ratiometric measurement of the hydroxyl radical (˙OH). In the probe sensing system, the blue emission of coumarin dye (coumarin-3-carboxylic acid, CCA) immobilized on the nanoparticle surface is selectively enhanced by ˙OH due to the formation of a coumarin hydroxylation product with strong fluorescence, whereas the emission of red fluorescent dye encapsulated in the silica nanoparticle is insensitive to ˙OH as a self-referencing signal, and so the probe provides a good quantitative analysis based on ratiometric fluorescence measurement with a detection limit of 1.65 μM. Moreover, the probe also shows high selectivity for ˙OH determination against metal ions, other reactive oxygen species and biological species. More importantly, it exhibits low cytotoxicity and high biocompatibility in living cells, and has been successfully used for cellular imaging of ˙OH, showing its promising application for monitoring of intracellular ˙OH signaling events.

Formaldehyde, a volatile organic compound that is ubiquitous in gas pollutants, has an indelible hazard to the health system of humans. Development of simple and convenient ways for the visual detection of formaldehyde in air is still of importance and challenging. In this paper, we report a new type of fluorescence enhancement probe (FAP), which directly exhibited fluorescence enhancement response to formaldehyde with high sensitivity and selectivity. The FAP was synthesized through the substitution reaction between hydrazine and NBD (7-nitrobenzo-2-oxa-1, 3-diazolyl) chloride, that the hydrazine group acted as both fluorescence quencher based on the photo-induced electron transfer (PET) pathway and reaction triggering factor for selectively recognizing formaldehyde. When the FAP was incubated with a formaldehyde-containing circumstance, Schiff base compound was produced by means of the aldimine condensation reaction which inhibited the PET pathway from hydrazine group to NBD, and thus turned on the fluorescence of the FAP significantly. It is worth mentioning that the FAP showed more remarkable response to formaldehyde under acid conditions. Under the optimal experimental conditions, the FAP responded linearly toward formaldehyde in a wide range of 0.015–0.8 mg•L−1, while the fluorescence enhancement was close to 30 times. This FAP was successfully used to detect gaseous formaldehyde in indoor air.

Metal-organic framework is an extended coordination compound with repeating coordination entities and voids, which shows potential applications in gas storage, separation, catalysis, and etc. This work reports the synthesis of a new functional metal-organic framework of pyromellitic acid and europium, and its application in fluorescence sensing of doxycycline, a broad-spectrum polyketide antibiotic on the basis of fluorescence turn-on method. The metal-organic framework was initially non-fluorescent, however, with the addition of doxycycline, the system exhibited significant fluorescence enhancement at 526 nm and 617 nm, where both fluorescence intensities showed good linear correlations with the doxycycline concentration, suggesting the possibility for direct two-channel detection without any sensitization materials such as metal particles or surface-modified quantum dots. More interestingly, the unique fluorescence response of the system could discriminate doxycycline from other tetracycline antibiotics with high selectivity, and a limit of detection (LOD) was estimated to be 47 nM. It has been further demonstrated that the material has been successfully applied as sensing materials for selective determination of doxycycline in real samples of fish and urine.

New selective and sensitive fluorescence probes have always been in great demand for carbon monoxide, an important gasotransmitter molecule, which is involved in critical physiological and pathophysiological processes in the mammalian cardiovascular system. In this work, we synthesized a new palladacycle compound as a fluorescence turn-on probe for selective and quantitative detection of carbon monoxide. The weakly fluorescent probe quickly and selectively reacts with carbon monoxide and releases a highly fluorescent benzimidazole moiety, due to protonolysis of the palladacycle, which greatly enhances the fluorescence intensity. The selective reaction was against interference from other possible coexisting reactive oxygen species, and achieved a detection limit of ∼0.06 μM. Furthermore, the fluorescence turn-on probe was demonstrated with a high cellular uptake rate and was successfully applied for cell imaging of carbon monoxide in living cells.

Mercury is widely used in industry and easily leads to environmental pollution if discharged without proper waste control. On-site visual detection of mercuric ion is thus in demand and remains a great challenge. We herein demonstrate a detection method for rapid and on-site visualization of mercuric ion on the basis of integrating green-emissive imidazol fluorophore (PIPT) and red-emissive quantum dots (QDs) embedded in silica nanospheres. Such a nanohybrid fluorescent probe exhibits dual emissions at 500 nm and 657 nm under a single excitation wavelength. Due to the high chelating ability of PIPT toward mercuric ion, the fluorescence of PIPT could be selectively quenched while the fluorescence of the QDs is almost constant, leading to a distinct fluorescence color change from green to red, which can be applied for the rapid visualization of mercuric ion. This ratiometric fluorescent approach shows high sensitivity, high selectivity and anti-interference toward mercury against other metal ions. The detection limit of this method is determined to be 6.5 nM. The probe has also been successfully demonstrated for the determination of mercuric ion in real water samples.

A novel nanohybrid ratiometric fluorescence probe for on-site and visual determination of nitrogen dioxide (NO2) has been designed. The hybrid probe comprises blue-colored fluorescence carbon nanodots (CDs) and red-colored emission CdTe quantum dots (QDs). Such hybridized probe exhibits dual emission bands centered at 460 and 665 nm, respectively. The blue fluorescence of CDs is insensitive to the analyte, whereas the red emission of QDs is specifically quenched by the analyte, resulting in a distinguishable color change from orange-red to blue upon exposure to NO2. The limit of detection for nitrogen dioxide is estimated to be 19 nM in aqueous solution. More importantly, the nanohybrid probe has been successfully applied in visual detection of gaseous NO2 with a detection limit of 1 ppm, suggesting its potential application for NO2 sensing.

Among various fluorescence nanomaterials, the II-VI semiconductor nanocrystals (usually called quantum dots, QDs) should be very promising in sensing application because of their high quantum yields, capability for surface property manipulation, and unlimited possible chemical reactions. Herein, we present a fluorescence probe for hydrogen sulfide, which was prepared by first encapsulating inorganic cadmium telluride (CdTe) QDs in silica nanospheres, and subsequently engineering the silica surface with functional molecules azidocoumarin-4-acetic acid reactive to hydrogen sulfide. The nanohybrid probe exhibited two fluorescence bands centered at 452 and 657 nm, respectively. The red fluorescence at 657 nm of the nanohybrid probe is stable against H2S, while the blue fluorescence is specifically sensitive to H2S. The probe showed a distinct fluorescence color evolution from light magenta to blue upon exposure to different amounts of H2S, and a detection limit of 7.0 nM was estimated in aqueous solution. We further applied the nanohybrid probe for visual detection of gaseous H2S with a low concentration of 0.5 ppm using glass indicating spots sensors, suggesting its potential application for gaseous H2S sensing. Such an efficient on-site visual determination of gaseous hydrogen sulfide (H2S) is highly demanded in on-site environmental monitoring and protection.

One-dimensional (1D) single-crystalline trigonal selenium nanorods (t-Se NRs) were prepared through a “solid–solution–solid” method by dispersing the prepared amorphous α-Se spheres in ethanol. The single crystal structure of the t-Se NRs could be excited under visible light, with a band gap of 1.56 eV. The t-Se NRs were found for the first time to display noticeable photocatalytic activity under visible light. In addition, the rate of photodegradation of methyl orange (MO) in the visible–Se NRs–H2O2 system (1.7 × 10−1 min−1) is about 17 times greater than that in the visible–Se NRs–HCl system with equal pH (1.0 × 10−2 min−1). Furthermore, we proposed a photocatalysis mechanism of the visible–Se NRs–H2O2 system based on electron paramagnetic resonance (EPR) characterization and studying the effect of different reactive species.

A new fluorescent molecule of an imidazole derivative was synthesized through simple cyclization of a hetero-aromatic compound and successfully applied for the rapid and ratiometric sensing of HOCl with high sensitivity and selectivity. It has also been demonstrated for the bioimaging of HOCl using A549 cells.

The highly fluorescent graphene oxide modified by hexylenediamine was fabricated to determinate the amount of hypochlorous acid (HOCl) in aqueous solution. The fluorescence of graphene oxide was quenched by HOCl based on the intramolecular charge-transfer (ICT) between grapheme oxide and chloramines, which formed through the oxidation of amino groups at the lateral edge of graphene oxide by HOCl. This method shows low interference and high selectivity for HOCl with a limit of detection of 3.5 μM in water. Additionally, the fluorescence graphene oxide with a quantum yield of 11.2% showed a good spike and recovery test for detection of HOCl in tap water, suggesting that the fluorescent probe is a potential strategy for the accurate determination of HOCl in realistic condition.

Functional quantum dots (QDs) grafted with ferric dithiocarbamate complex layers (QDs-Fe(III)(DTC)3) were fabricated and demonstrated to be selectively reactive to nitric oxide. The dithiocarbamate (DTC) was covalently conjugated to the amine-coated QDs by a condensation reaction of the carboxyl in DTC and the amino polymer in surface of QDs. The weak fluorescence of QDs-Fe(III)(DTC)3 was attributed to the energy transfer between CdSe/ZnS and Fe(III)(DTC)3 complex at the surface of the functionalized quantum dots. Nitric oxide could greatly switch on the fluorescence of QDs-Fe(III)(DTC)3 by displacing the DTC in the Fe(III)(DTC)3 accompanied by reducing Fe(III) to Fe(II), thus shutting off the energy transfer way. The limit of detection for nitric oxide was estimated to be 3.3 μM and the specific detection was not interfered with other reactive oxygen species. Moreover, the probe was demonstrated for the sensing of gaseous nitric oxide, and the visual detection limit was as low as 10 ppm, showing the potential for sensing nitric oxide by the naked eye.

Taking advantage of a nitrogen dioxide (NO2)-selective probe reported by our group previously, we have developed a fluorescent assay for quantifying NO2 absorbance capacity of flavanols and related polyphenolic compounds. A non-fluorescent NiII dithiocarbamate complex containing sulforhodamine fluorophore reacted rapidly and selectively with NO2 and turned on the fluorescence of the rhodamine. In the presence of radical scavengers, such as tea catechins, the rates of the fluorescence turning on by NO2 were suppressed in a dose-dependent manner. When a simple kinetic equation of the initial reaction rates is applied, the rate constants of the antioxidant reaction with NO2 can be derived using epicatechin as a reference standard, and the value is comparable to that obtained by the pulse radiolysis method. The scavenging capacity against NO2 of nine common phenolic compounds was evaluated, and their structure–activity relationship was also established. Additionally, the mechanism behind NO2 scavenging by phe...

Herein, for the detection of highly explosive 2,4,6-trinitrotoluene (TNT) instantly and on-site, a fluorescence ratiometric probe using a dual-emission nanohybrid has been developed. The nanohybrid comprises blue-colored fluorescent graphene oxide (FGO) being conjugated with red-emitting manganese-doped ZnS nanocrystals (ZnS:Mn NCs), the latter being functionalized with hexamethylenediamine. The blue fluorescence of FGO is insensitive to TNT and is used as an internal reference, whereas the red fluorescence of ZnS:Mn NCs can be selectively quenched by TNT through electron transfer, resulting in a unique red-purple-blue color response as the amount of TNT is increased. Thus, the probe could be used for the quantitative measurement of TNT based on the fluorescence ratiometric method. We demonstrated that the nanohybrid probe exhibited high visual detection sensitivity and reliability in comparison with single-color fluorescence quenching probes. A fluorescence test paper was prepared using the nanohybrid probe and was demonstrated to detect TNT residues directly on various surfaces including rubber, a person's fingers and manila envelopes with a visual detection limit as low as 5.68 ng mm(-2), showing its promising application for security screening.

A near-infrared (NIR) fluorescent probe was synthesized and demonstrated to be highly selective in reaction with hypochlorous acid (HOCl), an endogenous reactive oxygen species (ROS) produced by myeloperoxidase in neutrophils. The reaction with HOCl resulted in the NIR fluorescence quenching at 774 nm and the absorbance decreasing at 710 nm, accompanied by the appearance of a new absorption band at 520 nm. The reaction mechanism was carefully examined and proposed to proceed by initial formation of chlorohydrins and subsequent degradation. This NIR fluorescent probe was successfully applied as a selective and sensitive indicator for HOCl on the basis of either colorimetry or fluorometry, which showed detection limits of 0.13 and 0.70 μM, respectively. In addition, the molecular probe was further demonstrated for NIR fluorescence imaging of HOCl in cells and for evaluating the enzymatic activity of myeloperoxidase in the HOCl generation by measuring absorbance change.

We synthesized the Ni(II) complexes with dithiocarbamate ligand derived from ortho and para isomers sulforhodamine B fluorophores and demonstrated they are highly selective in reaction with nitrogen dioxide (NO2). Comparing to the para isomer, the ortho isomer showed much greater fluorescence increase upon reaction with nitrogen dioxide, which led to oxidation and de-complexation of dithiocarbamate ligand from Ni(II). We applied this probe for visual detection of 1 ppm nitrogen dioxide in gas phase and fluorescence imaging of NO2 in macrophage cells treated with nitrogen oxide donor.

The sensitive and selective determination of fluoride ions is particularly significant in environmental protection, food safety, and health care products. In this work, a highly selective turn-on fluorescent probe for fluoride ions has been synthesized by simply functionalizing fluorescent isophthalaldehyde with silicone-oxygen bonding. The selectivity of the probe is based on the specific reactivity of the silyl group toward fluoride ions in aqueous solution. The nucleophilic substitution reaction of fluoride ions triggers the cleavage of the Si-O bond to release a strongly fluorescent product, which can be used for the determination of fluoride ions by fluorescence intensity enhancement. The probe molecules are specifically responsive and highly selective for the fluoride anion over other relevant anions and cations. This fluorescent probe also shows high photostability and exhibits good sensitivity for fluoride ions, and the limit of detection is as low as 67 ppb. We have demonstrated its application for on-site sensitive determination of fluoride ions for environmental monitoring and protection.

It is crucial to monitor intracellular pH values and their fluctuation since the organelles of cells have different pH distribution. Herein we construct a new small molecule fluorescent probe HBT-O for monitoring the subtle pH values within the scope of neutral to acid in living cells. The probe exhibited good water solubility, a marked turquoise to olivine emission color change in response to pH, and tremendous fluorescence hypochromatic shift of ∼50nm (1718cm-1) as well as the increased fluorescence intensity when the pH value changed from neutral to acid. Thus, the probe HBT-O can distinguish the subtle changes in the range of normal pH values from neutral to acid with significant fluorescence changes. These properties can be attributed to the intramolecular charge transfer (ICT) process of the probe upon protonation in buffer solutions at varied pH values. Moreover, the probe was reversible and nearly non-toxic for living cells. Then the probe was successfully used to detect pH fluctuation in living cells by exhibiting different fluorescence colors and intensity. These findings demonstrate that the probe will find useful applications in biology and biomedical research.

Hypochlorous acid (HOCl) is a kind of reactive oxygen species which plays an important role in biological process. HOCl detection is of great importance in disease prevention and treatment. Herein, a cyanine-based near-infrared (NIR) fluorescent probe for HOCl has been designed and synthesized. This probe can react with HOCl in a dose-response manner along with the fluorescence of the probe quenched, the reaction through an electrophilic addition to the double bond and subsequent oxidation reaction. Experiments indicate that the probe can be acted as a selective and sensitive indicator for HOCl and the limit of detection for HOCl is estimated to be 22 nM. What's more, this probe shows a low toxicity to cells and can be applied to visualize HOCl molecules in living cells. Therefore, the proposed method may make a significant contribution to HOCl detection.

In this paper, we report a benzothiazole-functionalized cyanine fluorescence probe and demonstrate that it is selectively reactive to bisulfite, an intermediate indicator for oxidative stress. The selective reaction can be monitored by distinct ratiometric fluorescence variation favorable for cell imaging and visualization. The original probe can be regenerated in high yield through the elimination of bisulfite from the product by peroxides such as hydrogen peroxide, accompanied by fluorescence turning on at 590 nm, showing a potential application for the detection of peroxides. We successfully applied this probe for fluorescence imaging of bisulfite in cancer cells (MCF-7) treated with bisulfite and hydrogen peroxide as well as a selective detection limit of 0.34 μM bisulfite in aqueous solution.

This paper reports a new nanosized anatase particle enhanced chemiluminescence sensor that utilizes the catalytic surface of anatase for sensitive detection of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). This chemiluminescence sensor was composed of anatase nanoparticles grafted with the nitrobenzoxadiazole (NBD) fluorophore, bis(2,4,6-trichlorophenyl)oxalate (TCPO), and hydrogen peroxide (H2O2). The chemiluminescence efficiency of the sensor has been greatly enhanced by 6 times compared with that in the absence of nano-anatase. However, 2,4-D could greatly suppress the chemiluminescence enhancement of anatase nanoparticles probably by adsorbing and competitively reacting with the activated hydrogen peroxide on the anatase surface. The phenomenon has been used to detect 2,4-D by monitoring the quenching of the chemiluminescence of the system. The limit of detection of the chemiluminescence sensor system was estimated to be as low as 0.33 nmol/L. The simple and sensitive sensor reported herein ex...

In this review, we systematically analyzed the complicated interrelationship between photoluminescent quantum dots (QDs) and reactive oxygen species of biological importance. QDs, when photoexcited, generate reactive oxygen species (ROS), which are partially blamed for the cytotoxicity of QDs. On the positive side, the ability of generating ROS by QDs are exploited in photodynamic therapy using QDs alone or in combination with QD-surface bound organic sensitizers via resonance energy transfer from QDs to the organic dyes. Lastly, depending on the chemical composition and the functionalization of the QDs, ROS are known to quench or switch-on the QD photoluminescence. The selectivity and sensitivity toward specific ROS can be achieved through judicious chemical modification of QD surface coating layers by taking into account the reactivity difference among different ROS. The flexible QD surface functionalization opens up the unprecedented possibility of designer-made nanoprobes for sensing and quantifying ROS of biological importance.

Herein, we report a novel approach to the rapid visual detection of gaseous sulfur dioxide (SO2) by manipulating the surface chemistry of 3-aminopropyltriethoxysilane (APTS)-modified quantum dots (QDs) using fluorescent coumarin-3-carboxylic acid (CCA) for specific reaction with SO2. The CCA molecules are attached to the surface amino groups of the QDs through electrostatic attraction, thus the fluorescence of CCA is greatly suppressed because of the formation of an ion-pair complex between the ATPS-modified QDs and CCA. Such an interaction is vulnerable to SO2 because SO2 can readily react with surface amino groups to form strong charge-transfer complexes and subsequently release the strongly fluorescent CCA molecules. The mechanism has been carefully verified through a series of control experiments. Upon exposure to different amounts of SO2, the fluorescent color of the nanoparticle-based sensor displays continuously changes from red to blue. Most importantly, the approach owns high selectivity for SO2 and a tolerance of interference, which enables the sensor to detect SO2 in a practical application. Using this fluorescence-based sensing method, we have achieved a visual detection limit of 6 ppb for gaseous SO2.

A weakly fluorescent complex derived from a binaphthol-benzimidazole ligand was designed and synthesized for hydrogen sulfide at different pH conditions. It was demonstrated that the probe showed the same reactivity to various hydrogen sulfide species in a broad range of pH values to generate highly fluorescent product through a displacement reaction mechanism, whereas the product's fluorescence spectrum exhibited a hypsochromic shift of ∼73 nm (2393 cm(-1)) as pH increased from neutral to basic, which can be used for distinguishing the various species of hydrogen sulfide. This turn-on fluorescence probe was highly selective and sensitive to hydrogen sulfide with a detection limit of 0.11 μM. It was then applied for evaluating the total content of sulfide (including hydrogen sulfide, hydrosulfide, and sulfide) as well as for the visual detection of gaseous H2S in air using a simple test paper strip.

Graphene oxide has widely been employed in various fields, but its structure and composition has still not been fully understood. Here we report that freshly prepared graphene oxide exhibits a large number of π-conjugated carbon radicals at its π-network plane, which result from the addition reaction of hydroxyl radicals from H2O2 onto the conjugated double bonds of graphene oxide. The π-conjugated carbon radicals can directly initiate the long-lasting visible chemiluminescence of luminol, which is even stronger than that obtained when horseradish peroxidase and H2O2 are used. Previously, graphene oxide was mainly reported to be a quencher of chemiluminescence instead. Remarkably, the reacted radicals can be regenerated, thereby enabling the repetitive initiation of chemiluminescence by re-treatment of graphene oxide. The results reported here provide a new understanding of the structure, properties, and applications of graphene oxide.

Photoinduced charge transfer and separation in chemically hybridized CdS-PVK nanocomposites is investigated by steady-state and time-resolved photoluminescence as well as photoconductivity measurements. The chemically hybridized CdS-PVK composites display a longer luminescence lifetime than the pure CdS nanoparticles. At the same time, they show an enhanced photoconductivity as compared with PVK. It is also found that the chemically hybridized Cd-PVK nanocomposites exhibit a higher photoconductivity than the CdS/PVK nano-blends at the same molar ratio. The photoluminescence and photoconductivity results are explained by fast interfacial charge transfer between the Q-CdS and PVK.

A fluorescent probe was synthesized and demonstrated to be highly selective and sensitive in the reaction with copper (II) ion, generating a large variation of the fluorescence intensity in a dose-response manner. The probe contains a dansyl moiety as fluorophore and a multidentate ligand for copper (II) ion recognition. The reaction of the molecular probe with copper (II) ion proceeds rapidly and irreversibly in a 1 to 1 stoichiometric way, leading to the production of stable copper (II) complex, which subsequently results in the quenching of fluorescence. The detection limit for copper (II) ion was measured to be about 2ppb. It was also shown that the probe has high selectivity for copper (II) ion and good anti-interference ability against other transition metal ions. The herein reported very simple and reliable fluorescence probe could be employed for copper (II) ion detection in many aspects.

Poly(N-vinylcarbazole) (PVK) was sulfonated with acetyl sulfate. SIMS and XPS measurements of the sulfonated PVK show that the sulfonation occurs on the carbazole moiety and that the degree of sulfonation (DS) increases linearly with the ratio of the sulfonating agent to PVK. The DS of PVK could be controlled within a range from 12% to 28% by varying the reagent ratio. GPC measurements demonstrate that the molecular weight of PVK did not change substantially after sulfonation. UV-vis and photoluminescence spectra indicate that the sulfonation caused little change in the electronic structure of the PVK molecules but reduced significantly its photoluminescence quantum efficiency.

The instant and on-site detection of trace aqueous mercuric ion still remains a challenge for environmental monitoring and protection. This work demonstrates a new analytical method and its utility for visual detection of aqueous Hg(2+) on the basis of a novel water-soluble CdSe-ZnS quantum dots (QDs) functionalized with a bidentate ligand of 2-hydroxyethyldithiocarbamate (HDTC). The fluorescence of the aqueous HDTC modified QDs (HDTC-QDs) could be selectively and efficiently quenched by Hg(2+) through a surface chelating reaction between HDTC and Hg(2+), and the detection limit was measured to be 1 ppb. Most interestingly, the orange fluorescence of the HDTC-QDs gradually changes to red upon the increasing amount of Hg(2+) added besides the decreasing of the fluorescence intensity. By taking advantage of this optical phenomenon, a paper-based sensor for aqueous Hg(2+) detection has been developed by immobilizing the HDTC-QDs on cellulose acetate paper which has low background fluorescence in the wavelength range. The paper-based sensor showed high sensitivity and selectivity for Hg(2+) visual detection. When Hg(2+) was dropped onto the paper-sensor, an obviously distinguishable fluorescence color evolution (from orange to red) could be clearly observed depending on the concentration of Hg(2+). The limit of detection of the visual method for aqueous Hg(2+) detection was as low as 0.2 ppm. The very simple and effective strategy reported here should facilitate the development of portable and reliable fluorescence chemosensors for mercuric pollution control.

To detect trace trinitrotoluene (TNT) explosives deposited on various surfaces instantly and on-site still remains a challenge for homeland security needs against terrorism. This work demonstrates a new concept and its utility for visual detection of TNT particulates on various package materials. The concept takes advantages of the superior fluorescent properties of quantum dots (QDs) for visual signal output via ratiometric fluorescence, the feasibility of surface grafting of QDs for chemical recognition of TNT, and the ease of operation of the fingerprint lifting technique. Two differently sized CdTe QDs emitting red and green fluorescences, respectively, have been hybridized by embedding the red-emitting one in silica nanoparticles and covalently linking the green-emitting one to the silica surface, respectively, to form a dual-emissive fluorescent hybrid nanoparticle. The fluorescence of red QDs in the silica nanoparticles stays constant, whereas the green QDs functionalized with polyamine can selectively bind TNT by the formation of Meisenheimer complex, leading to the green fluorescence quenching due to resonance energy transfer. The variations of the two fluorescence intensity ratios display continuous color changes from yellow-green to red upon exposure to different amounts of TNT. By immobilization of the probes on a piece of filter paper, a fingerprint lifting technique has been innovated to visualize trace TNT particulates on various surfaces by the appearance of a different color against a yellow-green background under a UV lamp. This method shows high selectivity and sensitivity with a detection limit as low as 5 ng/mm(2) on a manila envelope and the attribute of being seen with the naked eye.

The development of a simple and on-site assay for the detection of organophosphorus pesticed residues is very important for food safety and exosystem protection. This paper reports the surface coordination-originated fluorescence resonance energy transfer (FRET) of CdTe quantum dots (QDs) and a simple ligand-replacement turn-on mechanism for the highly sensitive and selective detection of organophosphorothioate pesticides. It has been demonstrated that coordination of dithizone at the surface of CdTe QDs in basic media can strongly quench the green emission of CdTe QDs by a FRET mechanism. Upon the addition of organophosphorothioate pesticides, the dithizone ligands at the CdTe QD surface are replaced by the hydrolyzate of the organophosphorothioate, and hence the fluorescence is turned on. The fluorescence turn on is immediate, and the limit of detection for chlorpyrifos is as low as ∼0.1 nM. Two consecutive linear ranges allow a wide determination of chlorpyrifos concentrations from 0.1 nM to 10 μM. Importantly, the fluorescence turn-on chemosensor can directly detect chlorpyrifos residues in apples at a limit of 5.5 ppb, which is under the maximum residue limit allowed by the U.S. Environmental Protection Agency. The very simple strategy reported here should facilitate the development of fluorescence turn-on chemosensors for chemo/biodetection.

The photoluminescence of nonfluorescent molecularly engineered quantum dots (QDs) with iron(III) dithiocarbamates was selectively switched on by nitric oxide. Such functional QDs consisted of CdSe-ZnS nanocrystals as fluorophores and surface bound tris(N-(dithiocarboxy)sarcosine)iron(III) as reactive centers for nitric oxide. The fluorescence of the QDs was quenched by energy transfer between the excited QD cores and the surface bound iron(III) dithiocarbamates due to their optical energy overlapping. Nitric oxide restored the fluorescence of the QDs through reduction of the surface bound iron(III) complexes to iron(I)-NO adducts and thus shutting down the energy transfer pathway. The fluorescence of the iron(III) complex engineered QDs was selectively and quantitatively restored by nitric oxide but not by other reactive oxygen species. Such a property of the functional QDs could be used for sensing nitric oxide based on the fluorescence "turn on" mechanism.

Highly photoluminescent graphene oxides with various amino acid functionalities (GO–AAs) were synthesized through surface grafting reactions. The quantum yields were measured to be up to 21%. We demonstrated that their photoluminescence was highly stable against photobleaching by continuous ultraviolet (UV) light irradiation. The fluorescence decay time of GO–AAs was measured up to 9.6 ns with excitation at 375 nm. We further applied the functional graphene oxides in cell culture experiments and found that they could be readily taken up by A549 cells. MTT viability assay of GO–glutamic acid on A549 cells was also carried out to show its low cytotoxicity. Such stained cells were alive and fluoresced even after incubating for three weeks, suggesting that the graphene oxides with amino acid functionalities had high biocompatibility and low cytotoxicity.

A novel nanohybrid ratiometric fluorescence probe comprised of fluorescent graphene oxide and quantum dots (QDs) has been prepared by bringing CdTe QDs of red fluorescence and fluorescent graphene oxide (FGO) of blue fluorescence together through electrostatic attraction and hydrogen bonding interaction between their surface functional groups including carboxyl and amine groups. The nanohybrid ratiometric fluorescence probe exhibits dual emissions at 450 and 650 nm under a single excitation wavelength and shows high sensitivity for the detection of ferrous ions in the presence of H₂O₂. Ferrous ions reacts with H₂O₂ to generate very reactive hydroxyl radicals which possess a strong oxidizing nature and easily capture the electrons from the surfaces of the CdTe QDs, leading to fluorescence quenching of the QDs and no effect on the fluorescence of the graphene oxide, which hence results in a great change of the fluorescence ratio. Moreover, the ratiometric fluorescence probe is not only extremely sensitive to ferrous ions, but is also selective over other biologically relevant metal cations. The changes of fluorescence colour ratios can be used for visual sensing applications for ferrous ions in the presence of hydrogen peroxide, and can also be used for the indication of the existence of hydrogen peroxide.

We report on the effect of hypochlorous acid (HClO) in the fluorescence emission of a fluorescent graphene oxide modified by hexylenediamine (GO-C6NH2). The synthesis process and the optical property of GO-C6NH2 were also introduced in detail. We found a strong quenching effect by HClO on the fluorescence emission of the fluorescent graphene oxide. The fluorescent quenching efficiency of GO-C6NH2 establish as a function of the amount of HClO, which the fluorescence intensity ratio is proportional to the different concentrations of HClO employed for the measurement. The results show that this fluorescent naomaterials are a promising tool for sensing trace HClO in tap water.