Fluoride detection with a colorimetric and fluorescent dual-mode chemosensor

We designed a colorimetric and fluorescent dual-mode chemosensor ADM ((E)-2-(((2-amino-4,5-dichlorophenyl)imino)methyl)-6-methoxyphenol) for detecting fluoride (F⁻). The sensor ADM can detect F⁻ by colour and fluorescence changes. The colour change is from colourless to yellow, and the fluorescence change is a yellow turn-on. With the results of Job plot and electrospray ionisation mass spectrometry, the reaction of F⁻ and ADM turned out to be a 1:1 binding. The detection limits for F⁻ of ADM were 5.00 μM in ultraviolet–visible and 4.16 μM in fluorescence. The detecting process of F⁻ by ADM was demonstrated by ultraviolet–visible and fluorescent titrations, electrospray ionisation mass spectrometry, proton nuclear magnetic resonance titration and theoretical calculations.     

Stability,structure, and antioxidant activity of astaxanthin crystal from Haematococcus pluvialis

Crystallized anthaxanthin was prepared through the cleaning crystallization method and the stabilities during thermal, lighting, and pH treatment, and antioxidant activities in vitro were evaluated. The structural characterizations of astaxanthin crystal were verified by ¹H, ¹³C NMR, and XRD analysis. The stability data showed that the astaxanthin crystal was more sensitive to heat, light, and pH compared to oleoresin. The sucrose had no outstanding influence on the astaxanthin crystal, while the stability of astaxanthin oleoresin slightly increased with the increase of sugar concentration. The XRD and nuclear magnetic resonance spectra elucidated that the astaxanthin crystal was all trans structure. The astaxanthin crystal showed the dominant 1,1′-diphenyl-2-picrylhydrazyl (IC₅₀ 18.65 μmol L⁻¹), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt˙⁺(21.1 μmol L⁻¹), •OH (IC₅₀ 49.46 μmol L⁻¹) and ferric reducing antioxidant power (IC₅₀ 81.60 μmol L⁻¹) activities. The investigated results would be helpful for improving the development of astaxanthin crystal in food products.     

Comparison of Two Enzyme Sequences for a Novel L-Malate Biosensor

Two novel amperometric biosensors for the determination of L -malic acid in food samples have been compared. Both sensors make use of a Clark-type O₂-electrode but differ in the enzymes used. The first sensor is composed of malate dehydrogenase (decarboxylating), also known as ‘malic enzyme’ (MDH(dec.), EC 1.1.1.40) and pyruvate oxidase (POP, EC 1.2.3.3). It covers a linear detection range from 1 μmol dm⁻³ to 0·9 mmol dm⁻³ L -malate, with a response time of 1·5 min (t₉₀) and a relative standard deviation of 3·5%. Measurements with real samples offered a good correlation with the standard enzymatic assay (difference ±7%). Stored at room temperature, the response of the sensor is constant for 8 days. The second biosensor is based on the three enzyme sequence malate dehydrogenase (MDH, EC 1.1.1.37), oxaloacetate decarboxylase (OAC, EC 4.1.1.3) and pyruvate oxidase (POP, EC 1.2.3.3). It has a non-linear calibration curve. Concentrations from 5 μmol dm⁻³ to 1 mmol dm⁻³ L -malate can be detected, within a response time of 1·5 min and with a relative standard deviation of 20%. The lower detection limit for L -malate is 2 μmol dm⁻³. The response is constant for 10 days when the sensor is stored at room temperature.     

Fluorescence resonance energy transfer sensor between quantum dot donors and neutral red acceptors and its detection of BSA in micelles

Bovine serum albumin in micelles was effectively detected by a fluorescence resonance energy transfer -based molecular sensor using CdTe quantum dots as energy donors and neutral red as energy acceptors. The fluorescence resonance energy transfer efficiency was enhanced by the construction of cetyltrimethylammonium bromide micelles, which significantly reduced the distance between the donor and the acceptor. The results indicated that the addition of the albumin easily leads to the fluorescence quenching of CdTe-neutral red fluorescence resonance energy transfer due to the formation of CdTe-albumin complexes which have weak affinity to CdTe and repels the dyes from CdTe surface. The fluorescence intensity of the CdTe-neutral red sensor quenched with the increasing concentration of albumin. The linear range of albumin was from 0.4 × 10⁻³ to 11.00 × 10⁻³ g L⁻¹. The detection limit was 0.13 g L⁻¹.     

In situ bismuth-film electrode for square-wave anodic stripping voltammetric determination of tin in biodiesel

A bismuth-film electrode (BiFE) was applied in square-wave anodic stripping voltammetry (SWASV) in order to determine Sn (IV) in biodiesel samples. In situ simultaneous deposition of tin and bismuth at −1.2 V for 90 s was carried out in a supporting electrolyte containing 0.1 mol L⁻¹ acetate buffer (pH 4.5) and 1.73 mmol L⁻¹ caffeic acid as the complexing agent. A single well-defined anodic stripping peak was observed at −0.58 V for the oxidation of Sn to Sn (II), which was used as the analytical signal. The calibration curve was obtained in the concentration range of 0.17–7.83 μmol L⁻¹ with the detection limit being 0.14 μmol L⁻¹ (r = 0.9990). Repeatability and reproducibility for the measurement of the current peak were characterized by relative standard deviations of 3.6% and 4.1%, respectively, for a 5.0 μmol L⁻¹ Sn (IV) solution (n = 10). The method was validated by comparing the results obtained with those provided by application of the atomic absorption spectroscopy technique.     

Effects of AOT reverse micelle extraction on structure and emulsifying properties of soybean protein

The present study aimed to investigate the forward and backward extraction efficiency, structure, and emulsifying properties of soybean proteins obtained through bis (2-ethylhexyl) sulfosuccinate sodium salt (AOT) reverse micelle, as well as their relationship. The results showed that the extraction efficiency was the highest with the forward extraction time of 25 min, pH of 3.0, temperature of 45°C, KCl concentration of 0.0 mol L⁻¹, and the backward extraction time of 10 min, pH of 4.0, temperature of 30°C, KCl concentration of 0.5 mol L⁻¹. Significant changes in the secondary structure and fluorescence intensity of soybean protein after AOT reverse micelle extraction were observed. More β-sheet structure and higher fluorescence intensity corresponded to the higher emulsion stability of soybean protein. The results indicated that reverse micelle extraction shows great application in food industry.     

Phenoxaphosphino‐Modified Xantphos‐Type Ligands in the Rhodium‐Catalysed Hydroformylation of Internal and Terminal Alkenes

The solubility of the modifying ligand is an important parameter for the efficiency of a rhodium‐catalysed hydroformylation system. A facile synthetic procedure for the preparation of well‐defined xanthene‐type ligands was developed in order to study the influence of alkyl substituents at the 2‐, and 7‐positions of the 9,9‐dimethylxanthene backbone and at the 2‐, and 8‐positions of the phenoxaphosphino moiety of ligands 1 – 16 on solubility in toluene and the influence of these substituents on the performance of the ligands in the rhodium‐catalysed hydroformylation. An increase in solubility from 2.3 mmol⋅L⁻¹ to >495 mmol⋅L⁻¹ was observed from the least soluble to the most soluble ligand. A solubility of at least 58 mmol⋅L⁻¹ was estimated to be sufficient for a large‐scale application of these ligands in hydroformylation. Highly active and selective catalysts for the rhodium‐catalysed hydroformylation of 1‐octene and trans‐2‐octene to nonanal, and for the hydroformylation of 2‐pentene to hexanal were obtained by employing these ligands. Average rates of >1600 (mol aldehyde) × (mol Rh)⁻¹×h⁻¹ {conditions: p(CO/H₂) = 20 bar, T = 353 K, [Rh] = 1 mM, [alkene] = 637 mM} and excellent regio‐selectivities of up to 99% toward the linear product were obtained when 1‐octene was used as substrate. For internal olefins average rates of >145 (mol aldehyde)×(mol Rh)⁻¹×h⁻¹ {p(CO/H₂) = 3.6–10 bar, T = 393 K, [Rh] = 1 mM, [alkene] = 640–928 mM} and high regio‐selectivities up to 91% toward the linear product were obtained.     

Graft polymerization of methyl methacrylate onto polyvinyl alcohol using Ce4+ initiator

Methyl methacrylate (MMA) was graft polymerized onto polyvinyl alcohol (PVA) using ceric ammonium sulfate as an initiator in aqueous medium. The grafting efficiency of MMA was studied as a function of monomer and initiator concentration, time, pH, and temperature. Grafting efficiency was found to be optimum at a particular level of ceric ammonium sulfate (3.16 × 10⁻³ mol L⁻¹), PVA (1.0 g L⁻¹), MMA (0.469 mol L⁻¹), H₂SO₄ (0.188 mol L⁻¹), temperature (45°C), and time (4 h). The probable reasons for the influence of reaction variable on the observed trend of MMA towards grafting have been discussed. Acid hydrolysis and infrared spectroscopy were used for the confirmation of graft copolymer formation. Thermogravimetric analysis of PVA and a representative graft copolymer were studied. The solubility/swellability and the gelatinization characteristics are also reported. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 523–527, 1998     

Influence of different reactor types on Nannochloropsis oculata microalgae culture for lipids and fatty acid production

Greenhouse gases emitted into the atmosphere by burning of fossil fuels cause global warming. One option is obtaining biodiesel. Nannochloropsis oculata was cultured under different light intensities and reactors at 25°C for 21 days with f/2 medium to assess their effects on cell density, lipid, and fatty acids (FAs). N. oculata improved cell density on fed-batch glass tubular reactor (7 L) at 200 μmol E m⁻² s⁻¹, yielding 3.5 × 10⁸ cells ml⁻¹, followed by fed-batch Erlenmeyer flask (1 L) at 650 μmol E m⁻² s⁻¹ with 1.7 × 10⁸ cells ml⁻¹. The highest total lipid contents (% g lipid × g dry biomass⁻¹) were 44.4 ± 0.8% for the reactor (1 L) at 650 μmol E m⁻² s⁻¹ and 35.2 ± 0.2% for the tubular reactor (7 L) at 200 μmol E m⁻² s⁻¹, until twice as high compared with the control culture (Erlenmeyer flask 1 L, 80 μmol E m⁻² s⁻¹) with 21.2 ± 1%. Comparing the total lipid content at 200 μmol E m⁻² s⁻¹, tubular reactor (7 L) and reactor 1 L achieved 35.2 ± 0.2% and 28.3 ± 1%, respectively, indicating the effect of shape reactor. The FAs were affected by high light intensity, decreasing SFAs to 2.5%, and increased monounsaturated fatty acids + polyunsaturated fatty acids to 2.5%. PUFAs (20:5n-3) and (20:4n-3) were affected by reactor shape, decreasing by half in the tubular reactor. In the best culture, fed-batch tubular reactor (7 L) at 200 μmol E m⁻² s⁻¹ contains major FAs (16:0; 38.06 ± 0.16%), (16:1n-7; 30.74 ± 0.58%), and (18:1n-9; 17.15 ± 0.91%).     

A CMP-based [FeFe]-hydrogenase dual-functional biomimetic system for photocatalytic hydrogen evolution coupled with degradation of tetracycline

A novel bio-inspired conjugated microporous polymer (CMP) had been designed, synthesized and characterized. The mimics of [FeFe]-hydrogenase active sites were covalently attached to the CMP skeleton, which facilitates charge transfer between the light-harvesting moiety and active sites, and exhibited high performance in visible-light photocatalytic hydrogen evolution (2120 μmol·h⁻¹·g⁻¹) in an aqueous solution. The flower-like morphology, covalently linked framework and the “single active-site” effect derived from the porous skeleton were deemed to go a long way toward boosting the properties above. Interestingly, when the electron sacrifice agent (triethanolamine) was replaced by tetracycline, the CMP-based photocatalyst maintained the capability of photocatalytic hydrogen production (370 μmol·h⁻¹·g⁻¹) and realized efficient photodegradation of tetracycline simultaneously. This work provides a heuristic green dual-function strategy for constructing a sustainable and efficient photocatalytic system for hydrogen evolution with concurrent antibiotic residue degradation.     

Bisphenol A sensing based on surface molecularly imprinted, ordered mesoporous silica

Molecularly imprinted, ordered mesoporous silica was synthesized using bisphenol A (BPA) as the template and 3-aminopropyltriethoxysilane modified with hexagonally structured mesoporous silica (SBA-15) as the carrier. Carbon paste sensors were constructed by mixing the molecularly imprinted, ordered mesoporous silica with graphite powder and paraffin oil, and they were found to detect bisphenol A (BPA) with enhanced selectivity due to their ordered mesoporous structure and their successful molecular imprinting. The linear range for the proposed sensor was 1.000 × 10⁻⁷ mol L⁻¹ to 5.000 × 10⁻⁴ mol L⁻¹, and the detection limit was determined to be 3.222 × 10⁻⁸ mol L⁻¹. Overall, the sensor detected the water samples with satisfactory results.     

Preparation of polyacryloamidoxime chelating cloth for the extraction of heavy metals from water

Woven polyacryloamidoxime cloth was prepared from the polyacrylonitrile precursor via reaction in methanolic hydroxylamine. Preparation was controllable and reproducible and the reaction conditions were optimized with respect to the time of conversion, the concentration of NH₂OH⋅HCl, and the temperature of conversion. The cloth produced had a large capacity for Cu(II) and Pb(II) of 71.2 and 450 mg g^7minus;1 (1.12 and 2.17 mmol g⁻¹) respectively, and adequate physical properties suitable for rigorous use. Sorption profiles of Pb(II) and Cu(II) were similar to those of chelate ion exchange resins and fibers containing the amidoxime group. The rate of uptake of metals by the cloth was found to be dependent on the percent surface area converted to amidoxime groups, the concentration and type of metal being tested for, and the time of exposure. Anomalous kinetics of sorption for Pb(II) and Cu(II) by cloth of increasing amidoxime group content were explained by a two-part sorption mechanism. Distribution coefficients of 3.5 × 10⁶ and 1.5 × 10⁶ for Cu(II) and Pb(II) were observed, and the average rates of uptake for Cu(II) and Pb(II) were 600 and 200 μg g⁷⁻¹ day⁻¹ (9.4 and 0.96 μmol g⁷⁻¹ day⁻¹), respectively, from dilute solution ([Cu] = 5.9 μg L⁻¹, [Pb] = 2.8 μg L⁻¹). Treatment of the cloth with aqueous NaOH did not improve the capacities for Pb(II) and Cu(II). © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1175–1192, 1997     

Sensitive detection of rutin based on β-cyclodextrin@chemically reduced graphene/Nafion composite film

An electrochemical sensor based on chemically reduced graphene (CRG) was developed for the sensitive detection of rutin. To construct the base of the sensor, a novel composite was initially fabricated and used as the substrate material by combining CRG and β-cyclodextrin (β-CD) via a simple sonication-induced assembly. Due to the high rutin-loading capacity on the electrode surface and the upstanding electric conductivity of graphene, the electrochemical response of the fabricated sensor was greatly enhanced and displayed excellent analytical performance for rutin detection from 6.0 × 10⁻⁹ to 1.0 × 10⁻⁵ mol L⁻¹ with a low detection limit of 2.0 × 10⁻⁹ mol L⁻¹ at 3σ. Moreover, the proposed electrochemical sensor also exhibited good selectivity and acceptable reproducibility and could be used for the detection of rutin in real samples. Therefore, the present work offers a new way to broaden the analytical applications of graphene in pharmaceutical analysis.     

Tris (2,2′-bipyridil) copper (II) chloride complex: a biomimetic tyrosinase catalyst in the amperometric sensor construction

The use of tris (2,2′-bipyridil) copper (II) chloride complex, [Cu(bipy)₃]Cl₂·6H₂O, as a biomimetic catalyst, is reported in the construction of an amperometric sensor for dopamine. The sensor was prepared modifying a glassy carbon electrode with a Nafion® membrane doped with the complex. The optimized conditions for the sensor response were obtained in 0.25 mol dm⁻³ Pipes buffer (pH 7.0) containing 150 μmol dm⁻³ H₂O₂, with an applied potential of −50 mV versus saturated calomel electrode (SCE). In these conditions, a linear response range between 9 and 230 μmol dm⁻³, with a sensitivity of 1.43±0.01 nA dm³ μmol⁻¹ cm⁻² and a detection limit of 4.8 μmol dm⁻³ were observed for dopamine. The response time for this sensor was about 1 s, presenting the same response for at least 150 successive measurements, with a good repeatability (4.8%) expressed as relative standard deviation for n=13. After its construction, this sensor can be used after 180 days without loss of sensitivity, kept at room temperature. The difference of the sensor response between four preparations was 4.2%. A detailed investigation about the sensor response for other eighteen phenolic compounds and five interfering species was performed. The sensor was applied for dopamine determination in pharmaceutical preparation with success.     

Synthesis of secondary amine-based fluorescent porous organic polymers via Friedel–Crafts polymerization reaction for adsorbing and fluorescent sensing iodine

We present the preparation and characterization of a novel class of secondary amine-based porous organic polymers (POPs: TDPA and TTPBTA), and their iodine adsorption, fluorescence sensing properties for the first time. Two secondary amine-based POPs were synthetized by Friedel−Crafts polymerization reaction catalyzed via methylsulfonic acid with yields of 22.51 and 54.44%. The thermal stability of resulting POPs run up to above 268 and 568°C, and their BET specific surface areas are 56.5 and 2.49 m² g⁻¹, respectively. Their iodine adsorption and fluorescent sensing properties are comparable to that of triphenylamine (TPA)-based (tertiary amine) POPs. The resulting POPs display excellent sorption abilities to iodine molecules with the iodine adsorption capacity of about 3.93 and 1.64 g g⁻¹. Adsorbed iodine is easily desorbed by heating or washing with organic solvents, which make them reusable. They can also adsorb iodine from cyclohexane solution. Moreover, the POPs possess excellent fluorescent sensing property for I₂ with Ksv of 1.85 × 10⁴ and 6.56 × 10⁴ L mol⁻¹, as well as the limits of detection (LODs) of 1.62 × 10⁻¹¹ and 6.86 × 10⁻¹² mol L⁻¹. The performance of adsorbing and fluorescence sensing iodine can be explained by electron transfer mechanism.     

Live-Cell Sensing of Telomerase Activity by Using Hybridization-Sensitive Fluorescent Oligonucleotide Probes

Live-cell sensing of telomerase activity with simple and efficient strategies remains a challenging target. In this work, a strategy for telomerase sensing by using hybridization-sensitive fluorescent oligonucleotide probes is reported. In the presence of telomerase and dNTPs, the designed supporting strand was extended and generated the hairpin structure that catalyzed the next telomerase extending reaction. The special extension mechanism increased the local concentration of another supporting strand and telomerase, which resulted in enhanced telomerase activity. The hybridization-sensitive oligonucleotide probes bound to the hairpin catalyst and generated turn-on fluorescence. This method realized the sensing of telomerase activity in HeLa cell extract with a detection limit below 1.6×10⁻⁶ IU μL⁻¹. The real-time in situ observation of telomerase extension was achieved in living HeLa cells. This strategy has been applied to monitor the efficiency of telomerase-targeting anticancer drugs in situ.     

Zinc ion-imprinted polymer based on silica particles modified carbon paste electrodes for highly selective electrochemical determination of zinc ions

ABSTRACT

In this study, Zn(II) ion-imprinted polymer was prepared on the surface of vinyl silica particles and applied for detection of Zn(II) ions using differential pulse voltametry. The ion- imprinted polymer particles were prepared by free radical polymerization. The prepared particles were characterized by different morphological and elemental techniques. The ion-imprinted particles were used to fabricate the carbon paste electrode as a zinc ions sensor. The modified zinc sensor showed linear response in the concentration range 6.12 × 10^?9 to 4.59 × 10^?8 mol L^?1. The limit of detection and limit of quantification of the electrode were 1.351 × 10^?8 and 4.094 × 10^?8 mol L^?1, respectively.     

Electrochemical behavior and simultaneous determination of dihydroxybenzene isomers at a functionalized SBA-15 mesoporous silica modified carbon paste electrode

The simultaneous voltammetric determination of dihydroxybenzene isomers was investigated using cyclic and differential pulse voltammetries at the amino-functionalized SBA-15 mesoporous silica-modified carbon paste electrode (NH₂-SBA15/CPE) in phosphate buffer solution (pH 6.0). The NH₂-SBA15/CPE showed a larger peak current and higher selectivity for the dihydroxybenzene isomers in comparison with the bare carbon paste electrode (CPE) and SBA-15 mesoporous silica-modified carbon paste electrode (SBA15/CPE). The oxidation peak potential difference between hydroquinone (HQ) and catechol (CC) was 115 mV and was 396 mV between catechol and resorcinol (RC). This indicated that catechol, resorcinol and hydroquinone could be identified entirely at the NH₂-SBA15/CPE. Under the optimized conditions, the amperometric currents were linear over ranges from the following: 0.8–160 μmol L⁻¹ for hydroquinone, 1.0–140 μmol L⁻¹ for catechol and 2.0–160 μmol L⁻¹ for resorcinol. The detection limits were 0.3, 0.5 and 0.8 μmol L⁻¹, respectively. The proposed electrode can be applied to the simultaneous determination of dihydroxybenzene isomers in mixtures without previous chemical or physical separations.     

Surface molecularly imprinted polymers based ZnO quantum dots as fluorescence sensors for detection of diethylhexyl phthalate with high sensitivity and selectivity

This work describes the preparation of molecularly imprinted polymers using ZnO quantum dots, which were used for the selective detection of diethylhexyl phthalate (DEHP). Methacrylic acid, ethylene glycol dimethacrylate, 2,2′‐azobis(2‐methylpropionitrile) and ZnO were used as functional monomer, crosslinker, initiator and optical material, respectively. Molecularly imprinted polymers were successfully synthesized, and the linear relationship between fluorescence intensity and amount was from 0.5 to 40 µmol L^?1 for DEHP. The coefficient of correlation was 0.9923 and the imprinting factor was 11.16. The results were above 97.50% and relative standard deviation below 3.86% for the detection of DEPH in actual water samples. This study could provide a novel method using molecularly imprinted polymers for highly selective and sensitive detection of DEHP. © 2018 Society of Chemical Industry     

Sensitive DNA impedance biosensor for detection of cancer, chronic lymphocytic leukemia, based on gold nanoparticles/gold modified electrode

A simple and sensitive DNA impedance sensor was prepared for the detection of chronic lymphocytic leukemia. The DNA electrochemical biosensor is worked based on the electrochemical impedance spectroscopic (EIS) detection of the sequence-specific DNA related to chronic lymphocytic leukemia. The ssDNA probe was immobilized on the surface of the gold nanoparticles. Compared to the bare gold electrode, the gold nanoparticles-modified electrode could improve the density of the probe DNA attachment and hence the sensitivity of the DNA sensor greatly. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy were performed in a solution containing 1.0 mmol L⁻¹ K₃[Fe(CN)₆]/K₄[Fe(CN)₆] and 50 mmol L⁻¹ phosphate buffer saline pH 6.87 plus 50 mmol L⁻¹ KCl. In the CV studied, the potential was cycled from 0.0 to +0.65 V with a scan rate of 50 mV s⁻¹. Using EIS, the difference of the electron transfer resistance (ΔR_et) was linear with the logarithm of the complementary oligonucleotides sequence concentrations in the range of 7.0 × 10⁻¹²–2.0 × 10⁻⁷ mol L⁻¹, with a detection limit of 1.0 × 10⁻¹² mol L⁻¹. In addition, the DNA sensor showed a good reproducibility and stability during repeated regeneration and hybridization cycles.