Ratiometric fluorescent detection of Cu2+ based on dual‐emission ZIF‐8@rhodamine‐B nanocomposites

Zeolitic imidazolate framework‐8 (ZIF‐8) loading rhodamine‐B (ZIF‐8@rhodamine‐B) nanocomposites was proposed and used as ratiometric fluorescent sensor to detect copper(II) ion (Cu²⁺). Scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray powder diffraction, nitrogen adsorption/desorption isotherms and fluorescence emission spectroscopy were employed to characterize the ZIF‐8@rhodamine‐B nanocomposites. The results showed the rhodamine‐B was successfully assembled on ZIF‐8 based on the π‐π interaction and the hydrogen bond between the nitrogen atom of ZIF‐8 and –COOH of rhodamine‐B. The as‐obtained ZIF‐8@rhodamine‐B nanocomposites were octahedron with size about 150–200 nm, had good water dispersion, and exhibited the characteristic fluorescence emission of ZIF‐8 at 335 nm and rhodamine‐B at 575 nm. The Cu²⁺ could quench fluorescence of ZIF‐8 rather than rhodamine‐B. The ZIF‐8 not only acted as the template to assemble rhodamine‐B, but also was employed as the signal fluorescence together with the fluorescence of rhodamine‐B as the reference to construct a novel ratiometric fluorescent sensor to detect Cu²⁺. The resulted ZIF‐8@rhodamine‐B nanocomposite fluorescence probe showed good linear range (68.4 nM to 125 μM) with a low detection limit (22.8 nM) for Cu²⁺ combined with good sensitivity and selectivity. The work also provides a better way to design ratiometric fluorescent sensors from ZIF‐8 and other fluorescent molecules.     

A coumarin‐based fluorescent turn‐on probe for detection of biothiols in vitro

A novel fluorescent probe (CA‐N) was designed and synthesized for detection of biothiols. CA‐N displayed a strong fluorescence in the presence of biothiols with high sensitivity, and the mechanism for detection biothiols was based on the Michael addition reaction of a thiol group to α,β‐unsaturated ketones. CA‐N showed low detection limit for cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), which were calculated as 3.16, 0.19 and 5.15 μM, respectively. At the same time, CA‐N exhibited high selectivity toward biothiols compared with other biological amino acids. In vitro cell experiments proved that CA‐N had no cytotoxicity, high cell permeability and could be employed in living cell imaging for biothiols. Copyright © 2015 John Wiley & Sons, Ltd.     

Formation mechanism of cross‐linking Maillard compounds in peptide–xylose systems

The formation mechanism of Maillard peptides was explored in Maillard reaction through diglycine/glutathione(GSH)/(Cys‐Glu‐Lys‐His‐Ile‐Met)–xlyose systems by heating at 120 °C for 30–120 min. Maximum fluorescence intensity of Maillard reaction products (MRPs) with an emission wavelength of 420~430 nm in all systems was observed, and the intensity values were proportional to the heating time. Taken diglycine/GSH–[¹³C₅]xylose systems as a control, it was proposed that the compounds with high m/z values of 379 and 616 have the high molecular weight (HMW) products formed by cross‐linking of peptides and sugar. In (Cys‐Glu‐Lys‐His‐Ile‐Met)–xylose system, the m/z value of HMW MRPs was not observed, which might be due to the weak signals of these products. According to the results of gel permeation chromatography, HMW MRPs were formed by Maillard reaction, especially in (Cys‐Glu‐Lys‐His‐Ile‐Met)–xylose system, the percentage of Maillard peptides reached 52.90%. It was concluded that Maillard peptides can be prepared through the cross‐linking of sugar and small peptides with a certain MW range. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Bovine serum albumin‐confined silver nanoclusters as fluorometric probe for detection of biothiols

Fluorescent bovine serum albumin‐confined silver nanoclusters (BSA–AgNCs) were demonstrated to be a novel and environmentally friendly probe for the rapid detection of biothiols such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH). The sensing was ascribed to the strong affinity between the mercapto group of the biothiols and the silver nanoclusters. The fluorescence intensity of BSA–AgNCs was quenched efficiently on increasing the concentration of biothiol, corresponding with a red‐shift in emission wavelength. However, the fluorescence of the silver nanoclusters was almost unchanged in the presence of other α‐amino acids at 10‐fold higher concentrations. By virtue of this specific response, a new, simple and rapid fluorescent method for detecting biothiols has been developed. The linear ranges for Cys, Hcy and GSH were 2.0 × 10^‐6 to 9.0 × 10^‐5 M (R² = 0.994), 2.0 × 10^‐6 to 1.2 × 10^‐4 M (R² = 0.996) and 1.0 × 10^‐5 to 8.0 × 10^‐5 M (R² = 0.980), respectively. The detection limits were 8.1 × 10^‐7 M for Cys, 1.0 × 10^‐6 M for Hcy and 1.1 × 10^‐6 M for GSH. Our proposed method was successfully applied to the determination of thiols in human plasma and the recovery was 94.83–105.24%. It is potentially applicable to protein‐stabilized silver nanoclusters in a chemical or biochemical sensing system. Copyright © 2014 John Wiley & Sons, Ltd.     

BSA–AuNPs@Tb–AMP metal–organic frameworks for ratiometric fluorescence detection of DPA and Hg2+

An easy and effective strategy for synthesizing a ratiometric fluorescent nanosensor has been demonstrated in this work. Novel fluorescent BSA–AuNPs@Tb–AMP (BSA, bovine serum albumin; AMP, adenosine 5′‐monophosphate; AuNPs, Au nanoparticles) metal–organic framework (MOF) nanostructures were synthesized by encapsulating BSA–AuNPs into Tb–AMP MOFs for the detection of 2,6‐pyridinedicarboxylic acid (DPA) and Hg²⁺. DPA could strongly co‐ordinate with Tb³⁺ to replace water molecules from the Tb³⁺ center and accordingly enhanced the fluorescence of Tb–AMP MOFs. The fluorescence of BSA–AuNPs at 405 nm remained constant. While the fluorescence of BSA–AuNPs at 635 nm was quenched after Hg²⁺ was added, the fluorescence of Tb–AMP MOFs remained constant. Accordingly, a ratiometric fluorescence nanosensor was constructed for detection of DPA and Hg²⁺. The ratiometric nanosensor exhibited good selectivity to DPA over other substances. The F₅₄₅/F₄₀₅ linearly increased with increase of DPA concentration in the range of 50 nM to 10 μM with a detection limit as low as 17.4 nM. F₆₃₅/F₄₀₅ increased linearly with increase of Hg²⁺ concentration ranging from 50 nM to 1 μM with a detection limit as low as 20.9 nM. Additionally, the nanosensor could be successfully applied for the determination of DPA and Hg²⁺ in running water.     

A new rhodamine‐based fluorescent chemodosimeter for mercuric ions in water media

A new rhodamine–ethylenediamine–nitrothiourea conjugate (RT) was synthesized and its sensing property as a fluorescent chemodosimeter toward metal ions was explored in water media. Analytical results from absorption and fluorescence spectra revealed that the addition of Hg²⁺ ions to the aqueous solution of the chemodosimeter RT caused a distinct fluorescence OFF–ON response with a remarkable visual color change from colorless to pink; however, no clear spectral and color changes were observed from other metal ions including: Zn²⁺, Cu²⁺, Cd²⁺, Pb²⁺, Ag⁺, Fe²⁺, Cr³⁺, Co³⁺, Ni²⁺, Ca²⁺, Mg²⁺, K⁺ and Na⁺. The sensing results and the molecular structure suggested that a Hg²⁺‐induced a desulfurization reaction and cyclic guanylation of the thiourea moiety followed by ring‐opening of the rhodamine spirolactam in RT are responsible for a distinct fluorescence turn‐on signal, indicating that RT is a remarkably sensitive and selective chemodosimeter for Hg²⁺ ions in aqueous solution. Hg²⁺ within a concentration range from 0.1 to 25 μM can be determined using RT as a chemodosimeter and a detection limit of 0.04 μM is achieved. Copyright © 2014 John Wiley & Sons, Ltd.     

Importance of the interaction protein–protein of the CaM–PDE1A and CaM–MLCK complexes in the development of new anti‐CaM drugs

Protein–protein interactions play central roles in physiological and pathological processes. The bases of the mechanisms of drug action are relevant to the discovery of new therapeutic targets. This work focuses on understanding the interactions in protein–protein–ligands complexes, using proteins calmodulin (CaM), human calcium/calmodulin‐dependent 3′,5′‐cyclic nucleotide phosphodiesterase 1A active human (PDE1A), and myosin light chain kinase (MLCK) and ligands αII–spectrin peptide (αII–spec), and two inhibitors of CaM (chlorpromazine (CPZ) and malbrancheamide (MBC)). The interaction was monitored with a fluorescent biosensor of CaM (hCaM M124C–mBBr). The results showed changes in the affinity of CPZ and MBC depending on the CaM–protein complex under analysis. For the Ca²⁺–CaM, Ca²⁺–CaM–PDE1A, and Ca²⁺–CaM–MLCK complexes, CPZ apparent dissociation constants (K_ds) were 1.11, 0.28, and 0.55 μM, respectively; and for MBC K_ds were 1.43, 1.10, and 0.61 μM, respectively. In competition experiments the addition of calmodulin binding peptide 1 (αII–spec) to Ca²⁺–hCaM M124C–mBBr quenched the fluorescence (K_d = 2.55 ± 1.75 pM) and the later addition of MBC (up to 16 μM) did not affect the fluorescent signal. Instead, the additions of αII–spec to a preformed Ca²⁺–hCaM M124C–mBBr–MBC complex modified the fluorescent signal. However, MBC was able to displace the PDE1A and MLCK from its complex with Ca²⁺–CaM. In addition, docking studies were performed for all complexes with both ligands showing an excellent correlation with experimental data. These experiments may help to explain why in vivo many CaM drugs target prefer only a subset of the Ca²⁺–CaM regulated proteins and adds to the understanding of molecular interactions between protein complexes and small ligands. Copyright © 2013 John Wiley & Sons, Ltd.     

Fluorimetric determination of proteins using 4‐chloro‐(2′‐hydroxylophenylazo)rhodanine–Ti(IV) complex as a spectral probe

A novel method for the determination of proteins was developed, based on the enhancement of fluorescence with 4‐chloro‐(2′‐hydroxylophenylazo)rhodanine–Ti(IV) [ClHARP–Ti(IV)] complex as a fluorescence probe. The excitation and emission wavelengths of the system were 335 nm and 376 nm, respectively. The presence of bis(2‐ethylhexyl)sulphosuccinate sodium salt (AOT) microemulsion greatly increased the sensitivity of the system. Under optimal conditions, four kinds of proteins, including bovine serum albumin (BSA), human serum albumin (HSA), egg albumin (Ova), and γ‐globin (γ‐G) were studied. The detection limits were 0.182 µg/mL for BSA, 0.0788 µg/mL for HSA, 0.216 µg/mL for Ova and 0.484 µg/mL for γ‐G. The linear ranges of the calibration were 0–12.0, 0–10.0, 0–18.0 and 0–18.0 µg/mL, respectively. The method possessed high sensitivity, good selectivity and was applied to the analysis of protein in milk powder and cornmeal with satisfactory results. Copyright © 2008 John Wiley & Sons, Ltd.     

Micellar‐based spectrofluorimetric method for the selective determination of ledipasvir in the presence of sofosbuvir: application to dosage forms and human plasma

A fast, low‐cost, sensitive, and selective spectrofluorimetric method for the determination of ledipasvir was developed and validated. The method is based on an enhancement in the native fluorescence intensity of ledipasvir by 500% of its original value by the formation of hydrogen bonds between the cited drug and Tween‐20 in the micellar system (pH = 5.0). All fluorescence measurements were carried out at 425 nm and 340 nm for emission and excitation wavelengths, respectively. A linear relationship between the concentration of ledipasvir and the observed fluorescence intensity was achieved in the range of 0.1–2.0 μg ml^?1 with 0.028, 0.084 μg ml^?1, for detection and quantitation limits, respectively. The acquired selectivity and sensitivity using the proposed method facilitate the analysis of ledipasvir in spiked human plasma with sufficient percentage recovery (95.36–99.30%). The proposed method was developed and validated according to International Council for Harmonisation (ICH) guidelines. Moreover, the cited drug was successfully determined in its pharmaceutical dosage form using the proposed method. In addition, the validity of the proposed results was statistically confirmed using Student's t‐test, variance ratio F‐test, and interval hypothesis test.     

Green synthesis of fluorescent carbon dots using chloroplast dispersions as precursors and application for Fe3+ ion sensing

Water‐soluble carbon dots (CDs) were synthesized using a one‐step hydrothermal treatment of chloroplast dispersions extracted from fresh leaves as a green carbon source. The CD solution showed an emission peak centred at 445 nm when excited at 300 nm. The synthesized CDs were uniform and monodispersed with an average size of 5.6 nm. When adding ferric(III) ions (Fe³⁺) to the solution of the original CDs, the fluorescence intensity decreased significantly. Based on the linear relationship between fluorescence intensity and concentration of Fe³⁺ ions, an effective method for rapid, sensitive and selective Fe³⁺ sensing in aqueous solution could be established. Under optimum conditions, the extent of the fluorescence quenching of prepared CDs strongly depended on the Fe³⁺ ions over a wide concentration range 1.0–100.0 μM with a detection limit (3σ/k) of 0.3 μM. Furthermore, the quantitative determination of Fe³⁺ ions in environmental water samples was realized.     

Characterization of the interaction of a mono‐6‐thio‐β‐cyclodextrin‐capped CdTe quantum dots–methylene blue/methylene green system with herring sperm DNA using a spectroscopic approach

Novel, water‐soluble CdTe quantum dots (QDs) capped with β‐cyclodextrin (β‐CD) and ~ 4.0 nm in diameter were synthesized in aqueous solution, and characterized using transmission electron microscopy (TEM). A fluorescence‐sensing system based on the photoinduced electron transfer (PET) of (mono‐6‐thio‐β‐CD)–CdTe QDs was then designed to measure the interaction of phenothiazine dyes [methylene blue (MB) and methylene green (MG)] with herring sperm DNA (hsDNA). This fluorescence‐sensing system was based on a fluorescence “OFF–ON” mode. First, MB/MG adsorbed on the surface of (mono‐6‐thio‐β‐CD)–CdTe QDs effectively quenches the fluorescence of (mono‐6‐thio‐β‐CD)–CdTe QDs through PET. Then, addition of hsDNA restores the fluorescence intensity of (mono‐6‐thio‐β‐CD)–CdTe QDs, because hsDNA can bind with MB/MG and remove it from the as‐prepared (mono‐6‐thio‐β‐CD)–CdTe QDs. In addition, detailed reaction mechanisms of the (mono‐6‐thio‐β‐CD)–CdTe QDs–MB/MG–hsDNA solution system were studied using optical methods, by comparison with the TGA–CdTe QDs–MB/MG–hsDNA solution system. Copyright © 2014 John Wiley & Sons, Ltd.     

Multifunctional organic–inorganic composite luminescent nanospheres

A simple general strategy was successfully developed for the preparation of magnetic–luminescent multifunctional nanocomposites by incorporating fluorescent (pyrene) and magnetic (Fe₃O₄) components simultaneously into a poly(styrene‐co‐methacrylic acid) [poly(St‐co‐MAA)] copolymer matrix. The nanospheres so prepared were characterized using scanning electron microscopy (SEM), powder X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The prepared magnetic–fluorescent inorganic–organic nanocomposites have excellent magnetic and photoluminescent properties. They can be used in magnetic separation of trace amounts of sample, fluorescence detection and imaging applications, including magnetic resonance imaging (MRI) and fluorescence imaging. The fluorescence quenching of the nanospheres in the presence of different amounts of Cu²⁺ ions was also investigated. Under optimal experimental conditions, the relative fluorescence intensity of the composite nanosphere colloidal solution is proportional to the concentration of Cu²⁺ ions, which indicates that these multifunctional nanocomposites can be used for the magnetic separation and fluorescence detection of Cu²⁺ ions. Copyright © 2011 John Wiley & Sons, Ltd.     

Paper mill sludge-based carbon quantum dots as a specifically ratiometric fluorescent probe for the sensitive and selective detection of coptisine

Coptisine (COP), one of the bioactive components in Rhizoma Coptidis, has many pharmacological effects. Meanwhile, the determination of COP is essential in pharmacological and clinical applications. Herein, we prepared carbon quantum dots (CQDs) by one-step oil-thermal method using paper mill sludge (PMS) as precursor, and developed a ratiometric fluorescence method for the determination of COP. The structural and optical properties of PMS-CQDs were evaluated through high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), ultraviolet-visible (UV-vis), fluorescence, zeta potential and fluorescence lifetime experiments. Fluorescence intensity ratio at 550 nm and 425 nm (I₅₅₀/I₄₂₅) was recorded as an index for quantitative detection of COP. The detection concentration of COP ranges from 0.1 to 50 μM in good linear correlation (R² = 0.9974) with a limit of detection of 0.028 μM (3σ/k). The quenching mechanism was deduced to be inner filter effect and static quenching. The ratiometric fluorescent probe showed impressive selectivity and sensitivity towards COP, and was successfully applied to the detection of COP in human urine with expected recoveries (95.22–111.00%) and relative standard deviations (0.46–2.95%), indicating that our developed method has a great application prospect in actual sample detection.     

Ultrafast liquid chromatographic analysis of erdosteine in human plasma based on fluorimetric detection and precolumn derivatization with 4‐bromomethyl‐7‐methoxycoumarin: Application to pharmacokinetic studies

In this study, a new analytical method for erdosteine (ERD) in plasma based on high‐performance liquid chromatography and a fluorimetric detector, is presented. Precolumn derivatization of ERD with 4‐bromomethyl‐7‐methoxy coumarin (BrMmC) and dibenzo‐18‐crown‐6‐ether as a reaction catalyst led to the production of a fluorescent compound. ERD was monitored by fluorescence with an excitation wavelength λ_ext. = 325 nm and emission wavelength λ_em. = 390 nm. Optimum reaction conditions were carefully studied and optimized. A chromatographic procedure was performed using a C18 column of 150 × 4.6 mm and 3 μm particle size and a mobile phase consisting of methanol:acetonitrile:water (30:30:40, v/v/v) under a flow rate of 0.5 ml min^?1. A calibration plot was established covering analyte concentration range 0.2–3.0 μg ml^?1; the detection limit was 0.015 μg ml^?1 and quantification limit was 0.05 μg ml^?1. Mean recovery was 87.33% and relative standard deviation was calculated to be less than 4.4%. The developed method was successfully used to determine pharmacokinetic preparations of ERD subsequent to administration of a 900 mg dose capsule to a healthy 40‐year‐old woman volunteer.     

Synthesis,characterization and fluorescent properties of cerium(III) glutathione complex

The cerium (III) glutathione complex was synthesized by the redox reaction of cerium (IV) with glutathione reduced (GSH) in aqueous solution. The Job‐plots indicate an ML (L = GSSG) stoichiometry of the complex. The fluorescent properties of the compound were investigated. The as‐prepared complex showed the characteristic maximum emission spectra of Ce(III) at 350 nm (λ_ex = 255 nm). The fluorescence results show that the Ce(IV) ions are first reduced to Ce(III), and then form Ce(III) complex after reacting with GSH. The complex was characterized by element analysis and FT‐IR spectra; the stability of the complex was analyzed by cyclic voltammeters and DSC‐TG as well. Finally, Ce(IV) was successfully employed to determine the concentrations of GSH in the presence of GSSG, in which the fluorescence intensities are proportional to the concentrations of GSH in the range of 1–100 nM with the detection limit of 0.05 nM of GSH, without interference from the presence of GSSG. Copyright © 2009 John Wiley & Sons, Ltd.     

Application of Exchangeable Biochemical Reactors with Oxidase‐Catalase‐Co‐immobilizates and Immobilized Microorganisms in a Microfluidic Chip‐Calorimeter

Several methods for the quantitative detection of different compounds, e.g., L‐amino acids, sugars or alcohols in liquid media were developed by application of an automatic measuring unit including a fluid chip‐calorimeter FCC‐21. For this purpose, enzymes were immobilized covalently on the inner and outer surface of CPG (controlled porous glass)‐spherules with an outer diameter of 100 μm and filled into a micro flow‐through reaction chamber (V_R = 20 μL). The design of the measuring cell allows for easy insertion into the calorimeter device of a stored series of comfortably pre‐fabricated measuring cells. These cells can be filled with different enzyme immobilizates. Different oxidases were used and co‐immobilized with catalase for the improvement of the detection sensitivity. A signal amplification could be achieved up to a factor of 3.5 with this configuration. β‐D‐glucose, ethanol and L‐lysine could be detected in a range of 0.25–1.75 mM using glucose oxidase, alcohol oxidase and lysine oxidase. The group of oxidases in combination with the enzymatic catalysis of the intermediate H₂O₂ allows the quantitative detection of a large number of analytes. A good measurement and storage stability could be achieved for several weeks by this immobilization method. In addition to enzyme‐based detection reactions, it was shown that living microorganisms can be immobilized in the reaction chamber. Thus, the system can be used as a whole‐cell biosensor. The quantitative detection of phenol in the range of 10–100 μM could be performed using the actinomycete Rhodococcus sp. immobilized on glass beads by means of embedding into polymers.     

Enantiomeric assay of escitalopram S(+)‐enantiomer and its “in‐process impurities” using two different techniques

The enantiomeric purity of escitalopram oxalate ESC and its “in‐process impurities,” namely, ESC‐N‐oxide, ESC‐citadiol, and R(?)‐enantiomer were studied in drug substance and products using high‐performance liquid chromatography (HPLC)‐UV (Method I), synchronous fluorescence spectroscopy (SFS) (Method IIA), and first derivative SFS (Method IIB). Method I describes as an isocratic HPLC‐UV for the direct resolution and determination of enantiomeric purity of ESC and its “in‐process impurities.” The proposed method involved the use of α_l‐acid glycoprotein (AGP) chiral stationary phase. The regression plots revealed good linear relationships of concentration range of 0.25 to 100 and 0.25 to 10 μg mL^?1 for ESC and its impurities. The limits of detection and quantifications for ESC were 0.075 and 0.235 μg mL^?1, respectively. Method II involves the significant enhancement of the fluorescence intensities of ESC and its impurities through inclusion complexes formation with hydroxyl propyl‐β‐cyclodextrin as a chiral selector in Micliavain buffer. Method IIA describes SFS technique for assay of ESC at 225 nm in presence of its impurities: R(?)‐enantiomer, citadiol, and N‐oxide at ?λ of 100 nm. This method was extended to (Method IIB) to apply first derivative SFS for the simultaneous determination of ESC at 236 nm and its impurities: the R(?)‐enantiomer, citadiol, and N‐oxide at 308, 275, and 280 nm, respectively. Linearity ranges were found to be 0.01 to 1.0 μg mL^?1 for ESC and its impurities with lower detection and quantification limits of 0.033/0.011 and 0.038/0.013 μg mL^?1 for SFS and first derivative synchronous fluorescence spectra (FDSFS), respectively. The methods were used to investigate the enantiomeric purity of escitalopram.     

Interaction of glucose‐derived carbon quantum dots with silver and gold nanoparticles and its application for the fluorescence detection of 6‐thioguanine

The interaction of glucose‐derived carbon quantum dots (CQDs) with silver (Ag) and gold (Au) nanoparticles (NPs) was explored by fluorescence spectroscopy. Both metal NPs cause an efficient quenching of CQD fluorescence, which is likely due to the energy transfer process between CQDs as donors and metal NPs as acceptors. The Stern–Volmer plots were evaluated and corresponding quenching constants were found to be 1.9 × 10¹⁰ and 2.2 × 10⁸ M^?1 for AgNPs and AuNPs, respectively. The analytical applicability of these systems was demonstrated for turn‐on fluorescence detection of the anti‐cancer drug, 6‐thioguanine. Because the CQD–AgNP system had much higher sensitivity than the CQD–AuNP system, we used it as a selective fluorescence probe in a turn‐on assay of 6‐thioguanine. Under optimum conditions, the calibration graph was linear from 0.03 to 1.0 μM with a detection limit of 0.01 μM. The developed method was applied to the analysis of human plasma samples with satisfactory results.     

A highly sensitive and selective fluorescent probe for fluoride anions based on intramolecular charge transfer

Currently, there is a great need to develop methods for the selective detection of fluoride anions (F^–) owing to their toxicity in the environment and biological function in living systems. In this study, we developed a new fluorescent probe (probe 1) employing a Si–O bond as a highly selective recognition receptor for detecting F^– via intramolecular charge transfer. Probe 1 could detect F^– quantitatively using the turn‐on fluorescence spectroscopy method with excellent sensitivity in the range of 4–38 μM and a detection limit of 0.26 μM; the detection time was < 17 min. We anticipate that probe 1 would be used widely to monitor F^– in the environment. Copyright © 2015 John Wiley & Sons, Ltd.     

Development of surface‐engineered yeast cells displaying phytochelatin synthase and their application to cadmium biosensors by the combined use of pyrene‐excimer fluorescence

The development of simple, portable, inexpensive, and rapid analytical methods for detecting and monitoring toxic heavy metals are important for the safety and security of humans and their environment. Herein, we describe the application of phytochelatin (PC) synthase, which plays a critical role in heavy metal responses in higher plants and green algae, in a novel fluorescent sensing platform for cadmium (Cd). We first created surface‐engineered yeast cells on which the PC synthase from Arabidopsis (AtPCS1) was displayed with retention of enzymatic activity. The general concept for the sensor is based on the Cd level‐dependent synthesis of PC₂ from glutathiones by AtPCS1‐displaying yeast cells, followed by simple discriminative detection of PC₂ via sensing of excimer fluorescence of thiol‐labeling pyrene probes. The intensity of excimer fluorescence increased in the presence of Cd up to 1.0 μM in an approximately dose‐dependent manner. This novel biosensor achieved a detection limit of as low as 0.2 μM (22.5 μg/L) for Cd. Although its use may be limited by the fact that Cu and Pb can induce cross‐reaction, the proposed simple biosensor holds promise as a method useful for cost‐effective screening of Cd contamination in environmental and food samples. The AtPCS1‐displaying yeast cells also might be attractive tools for dissection of the catalytic mechanisms of PCS. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1197–1202, 2013