Glucose oxidase-functionalized fluorescent gold nanoclusters as probes for glucose

Creation and application of noble metal nanoclusters have received continuous attention. By integrating enzyme activity and fluorescence for potential applications, enzyme-capped metal clusters are more desirable. This work demonstrated a glucose oxidase (an enzyme for glucose)-functionalized gold cluster as probe for glucose. Under physiological conditions, such bioconjugate was successfully prepared by an etching reaction, where tetrakis (hydroxylmethyl) phosphonium-protected gold nanoparticle and thioctic acid-modified glucose oxidase were used as precursor and etchant, respectively. These bioconjugates showed unique fluorescence spectra (λ_{em max} = 650 nm, λ_{ex max} = 507 nm) with an acceptable quantum yield (ca. 7%). Moreover, the conjugated glucose oxidase remained active and catalyzed reaction of glucose and dissolved O₂ to produce H₂O₂, which quenched quantitatively the fluorescence of gold clusters and laid a foundation of glucose detection. A linear range of 2.0 × 10⁻⁶–140 × 10⁻⁶ M and a detection limit of 0.7 × 10⁻⁶ M (S/N = 3) were obtained. Also, another horseradish peroxidase/gold cluster bioconjugate was produced by such general synthesis method. Such enzyme/metal cluster bioconjugates represented a promising class of biosensors for biologically important targets in organelles or cells.     

A study of complexation thermodynamic of humic acid with cadmium (II) and zinc (II) by Schubert's ion-exchange method

The complexation of humic acid from Azraq Oasis with two heavy metal ions Cd(II) and Zn(II) was investigated at pH 4 and 5 under constant ionic strength of 0.1 and at different temperatures (25, 35, 45, 55 and 65 °C). This investigation was done by using Schubert's ion-exchange equilibrium method, and its modified version.The derived conditional stability constants (log β_n) for these two metal-humate complexes were determined; they formed 1:1 and 1:2 complexes. It was found that the conditional stability constants (log β_n) increased by increasing pH and temperatures for all metal-humate complexes. It was found that the conditional stability constant log β₁ for Cd-humate is bigger than Zn-humate at all the desired temperatures and at pH 4 and 5.The derived constants and their temperature dependences have been used to calculate the corresponding thermodynamic parameters ΔG, ΔH, and ΔS, the results indicate that the stability of these complexes derives from very favorable entropy.     

Electrosyntheses of free-standing poly(dibenzo-18-crown-6) films in boron trifluoride diethyl etherate on stainless steel electrode

High-quality free-standing poly(dibenzo-18-crown-6) (PDBC) films with a conductivity of 4.1 × 10⁻² S cm⁻¹ and good thermal stability were synthesized electrochemically on stainless steel electrode by direct anodic oxidation of dibenzo-18-crown-6 (DBC) in pure boron trifluoride diethyl etherate (BFEE). In this medium, the oxidation potential onset of DBC was measured to be only 0.98 V vs. SCE, which was much lower than that in acetonitrile + 0.1 mol L⁻¹ Bu₄NBF₄ (1.45 V vs. SCE). PDBC films obtained from this medium showed good redox activity and stability in BFEE. The structural characterization of PDBC was performed using UV-vis, FTIR spectroscopy. The results of quantum chemistry calculations of DBC monomer and FTIR spectroscopy of PDBC films indicated that the polymerization mainly occurred at C₍₄₎ and C₍₅₎ positions). Fluorescent spectral studies indicated that PDBC was a blue light emitter. To the best of our knowledge, this is the first report on the electrodeposition of free-standing PDBC films.     

Fabrication of dissolved O2 metric uric acid biosensor using uricase epoxy resin biocomposite membrane

Uricase purified from 20-day-old leaves of cowpea was immobilized on to epoxy resin membrane with 80% retention of initial activity of free enzyme and a conjugation yield of 0.056 mg/cm². The uricase epoxy resin bioconjugate membrane was mounted over the sensing part of the combined electrode of ‘Aqualytic’ dissolved O₂ (DO) meter to construct a uric acid biosensor. The biosensor measures the depletion of dissolved O₂ during the oxidation of uric acid by immobilized uricase, which is directly proportional to uric acid concentration. The biosensor showed optimum response within 10-12 s at a pH 8.5 and 35 °C. A linear relationship was found between uric acid concentration from 0.025 to 0.1 mM and O₂ (mg/l) consumed. The biosensor was employed for measurement of uric acid in serum. The mean value of uric acid in serum was 4.92 mg/dl in apparently healthy males and 3.11 mg/dl in apparently healthy females. The mean analytic recoveries of added uric acid in reaction mixture (8.9 and 9.8 mg/dl) were 93.6 ± 2.34 and 87.18 ± 3.17% respectively. The within and between batch CVs were <6.5 and <5.0%, respectively. The serum uric acid values obtained by present method and standard enzymic colorimetric method, showed a good correlation (r = 0.996) and regression equation being y = 0.984x + 0.0674. Among the various metabolites tested only, glucose (11%), urea (38%), NaCl (25%) and cholesterol (13%) and ascorbic acid (56%) caused decrease, while, MgSO₄ and CaCl₂ had no effect on immobilized enzyme. The enzyme electrode showed only 32% decrease during its use for 100 times over a period of 60 days at 4 °C.     

Electrode modified with a composite film of ZnO nanorods and Ag nanoparticles as a sensor for hydrogen peroxide

A conducting fluorine-doped tin oxide (FTO) electrode, first modified with zinc oxide nanorods (ZnONRs) and subsequently attached with photosynthesized silver nanoparticles (AgNPs), designated as AgNPs/ZnONRs/FTO electrode, was used as an amperometric sensor for the determination of hydrogen peroxide. The first layer (ZnONRs) was obtained by chemical bath deposition (CBD), and was utilized simultaneously as the catalyst for the photoreduction of Ag ions under UV irradiation and as the matrix for the immobilization of AgNPs. The aspect ratio of ZnONRs to be deposited was optimized by controlling the number of their CBDs to render enough surface area for Ag deposition, and the amount of AgNPs to be attached was controlled by adjusting the UV-irradiation time. The immobilized AgNPs showed excellent electrocatalytic response to the reduction of hydrogen peroxide. The resultant amperometric sensor showed 10-fold enhanced sensitivity for the detection of H₂O₂, compared to that without AgNPs, i.e., only with a layer of ZnONRs. Amperometric determination of H₂O₂ at −0.55 V gave a limit of detection of 0.9 μM (S/N = 3) and a sensitivity of 152.1 mA M⁻¹ cm⁻² up to 0.983 mM, with a response time (steady-state, t₉₅) of 30-40 s. The selectivity of the sensor was investigated against ascorbic acid (AA) and uric acid (UA). Energy dispersive X-ray (EDX) analysis, transmission electron microscopic (TEM) image, X-ray diffraction (XRD) patterns, cyclic voltammetry (CV), and scanning electron microscopic (SEM) images were utilized to characterize the modified electrode. Sensing properties of the modified electrode were studied both by CV and amperometric analysis.     

An electrochemical on-field sensor system for the detection of compost maturity

A maturity sensor system was developed, based on the combination of three electrically measured parameters, pH, NH₄⁺ concentration, and phosphatase activity in the water extracts of compost samples. One of these parameters, the apparent phosphatase activity in crude test solutions was determined using screen-printed carbon strips (SPCSs) coated with α-naphthyl phosphate (α-NP) in Nafion film. The phosphatase activity was monitored in connection with differential pulse voltammetry (DPV) with an aliquot (30 μL) of the test solution on SPCS. The phosphatase activity sensor was validated using alkaline phosphatase (ALP) in Tris-HCl buffer (pH 8.0) and acid phosphatase (ACP) in citric acid buffer (pH 5.0). The activity of the spiked enzymes in the water extract of the compost sample could be confirmed with the change of corresponding oxidation peak current signal of the product, α-naphthol. The water extracts of compost samples (n = 24) collected in various composting days were applied to our compost maturity sensor system, and the conventional germination tests. Using multiple regression analysis, the germination index (GI) was expressed by the multi-linear regression equation consisting of pH, NH₄⁺ concentration, and the phosphatase activity. The calculated GI from the regression equation had a good correlation with the measured GI of the corresponding composts (r = 0.873). As a result, we have determined an equation for the determination of the compost stability using our portable sensor system rapidly at the composting site.     

Synthesis of boron suboxide (B6O) with ball milled boron oxide (B2O3) under lower pressure and temperature

Boron reacted with ball milled boron oxide under pressures between 1 and 5 GPa and at temperatures between 1300 and 1700 °C to afford boron suboxide (B₆O). Icosahedral B₆O grains with diameters ranging from 100 nm to 1.3 μm were prepared. The factors that affect the synthesis of B₆O are investigated. The best sample with crystal size up to 1.3 μm is obtained at 2 GPa and 1400 °C for 6 h. The indentation experiment gave an average Vickers hardness of 32.3 GPa for bulk B₆O sample, which is consistent with previous reports. Bulk B₆O sample exhibits oxidation resistance in air up to 1000 °C and mild oxidation in the temperatures of 1000-1200 °C, which is more oxidation resistant than diamond. It is possible that B₆O could be used as a substitute for diamond in industry because of its relatively mild synthesis conditions, high thermal stability and high hardness.     

Synthesis of 6-hydroxy-2-naphthoic acid from 2,6-diisopropylnaphthalene using NHPI as a key catalyst

A new strategy to 6-hydroxy-2-naphthoic acid (HNPA) and 4-hydroxybenzoic acid from 2,6-diisopropylnaphthalene and p-cymene, respectively, was developed using the NHPI-catalyzed aerobic oxidation as a principal reaction. 2,6-Diisopropylnaphthalene was oxidized by the oxidation with O₂ (1 atm) by NHPI (10 mol %) combined with Co(OAc)₂ (0.5 mol %) to give 6-acetyl-2-isopropylnaphthalene, which then was converted to 6-isopropyl-2-naphthoic acid under O₂ (1 atm) in the presence of Co(OAc)₂ (0.5 mol %) and Mn(OAc)₂ (0.5 mol %). Esterification of the resulting acid followed by the aerobic oxidation produced methyl 6-hydroxy-2-naphthoate whose hydrolysis led to the desired HNPA. An alternative route involves the oxidation of 6-acetyl-2-isopropylnaphthalene to 6-acetyl-2-naphthol on which subsequent oxidation and deacetylation gave HNPA. This method was successfully extended to the synthesis of 4-hydroxybenzoic acid from p-cymene.     

Glucose concentration determination based on silica sol-gel encapsulated glucose oxidase optical biosensor arrays

Optical biosensor arrays for rapidly determining the glucose concentrations in a large number of beverage and blood samples were developed by immobilizing glucose oxidase (GOD) on oxygen sensor layer. Glucose oxidase was first encapsulated in silica based gels through sol-gel approach and then immobilized on 96-well microarrays integrated with oxygen sensing film at the bottom. The oxygen sensing film was made of an organically modified silica film (ORMOSIL) doped with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium dichloride (Ru(dpp)₃Cl₂). The oxidation reaction of glucose by glucose oxidase could be monitored through fluorescence intensity enhancement due to the oxygen consumption in the reaction. The luminescence changing rate evaluated by the dynamic transient method (DTM) was correlated with the glucose concentration with the wide linear range from 0.1 to 5.0 mM (Y = 13.28X − 0.128, R = 0.9968) and low detection limit (0.06 mM). The effects of pH and coexisting ions were systemically studied. The results showed that the optical biosensor arrays worked under a wide range of pH value, and normal interfering species such as Na⁺, K⁺, Cl⁻, PO₄³⁻, and ascorbic acid did not cause apparent interference on the measurement. The activity of glucose oxidase was mostly retained even after 2-month storage, indicating their long-term stability.     

Simultaneous detection of ascorbate and uric acid using a selectively catalytic surface

The direct and selective detection of ascorbate at conventional carbon or metal electrodes is difficult due to its large overpotential and fouling by oxidation products. Electrode modification by electrochemical reduction of diazonium salts of different aryl derivatives is useful for catalytic, analytical and biotechnological applications. A monolayer of o-aminophenol (o-AP) was grafted on a glassy carbon electrode (GCE) via the electrochemical reduction of its in situ prepared diazonium salts in aqueous solution. The o-aminophenol confined surface was characterized by cyclic voltammetry. The grafted film demonstrated an excellent electrocatalytic activity towards the oxidation of ascorbate in phosphate buffer of pH 7.0 shifting the overpotential from +462 to +263 mV versus Ag/AgCl. Cyclic voltammetry and d.c. amperometric measurements were carried out for the quantitative determination of ascorbate and uric acid. The catalytic oxidation peak current was linearly dependent on the ascorbate concentration and a linear calibration curve was obtained using d.c. amperometry in the range of 2-20 μM of ascorbate with a correlation coefficient 0.9998, and limit of detection 0.3 μM. The effect of H₂O₂ on the electrocatalytic oxidation of ascorbate at o-aminophenol modified GC electrode has been studied, the half-life time and rate constant was estimated as 270 s, and 2.57 × 10⁻³ s⁻¹, respectively. The catalytically selective electrode was applied to the simultaneous detection of ascorbate and uric acid, and used for their determination in real urine samples. This o-AP/GCE showed high stability with time, and was used as a simple and precise amperometric sensor for the selective determination of ascorbate.     

Electrocatalytic oxidation behavior of guanosine at graphene, chitosan and Fe3O4 nanoparticles modified glassy carbon electrode and its determination

A graphene, chitosan and Fe₃O₄ nanoparticles (nano-Fe₃O₄) modified glassy carbon electrode (graphene-chitosan/nano-Fe₃O₄/GCE) was fabricated. The modified electrode was characterized by scanning electron microscope and electrochemical impedance spectroscopy. The electrochemical oxidation behavior of guanosine was investigated in pH 7.0 phosphate buffer solution by cyclic voltammetry and differential pulse voltammetry. The experimental results indicated that the modified electrode exhibited an electrocatalytic and adsorptive activities towards the oxidation of guanosine. The transfer electron number (n), transfer proton number (m) and electrochemically effective surface area (A) were calculated. Under the optimized conditions, the oxidation peak current was proportional to guanosine concentration in the range of 2.0 × 10⁻⁶ to 3.5 × 10⁻⁴ mol L⁻¹ with the correlation coefficient of 0.9939 and the detection limit of 7.5 × 10⁻⁷ mol L⁻¹ (S/N = 3). Moreover, the modified electrode showed good ability to discriminate the electrochemical oxidation response of guanosine, guanine and adenosine. The proposed method was further applied to determine guanosine in spiked urine samples and traditional Chinese medicines with satisfactory results.     

Electrochemical behaviors of guanosine on carbon ionic liquid electrode and its determination

The electrochemical behaviors of guanosine on the ionic liquid of N-butylpyridinium hexafluorophosphate (BPPF₆) modified carbon paste electrode (CPE) was studied in this paper and further used for guanosine detection. Guanosine showed an adsorption irreversible oxidation process on the carbon ionic liquid electrode (CILE) with the oxidation peak potential located at 1.12 V (vs. SCE) in a pH 4.5 Britton-Robinson (B-R) buffer solution. Compared with that on the traditional carbon paste electrode, small shift of the oxidation peak potentials appeared but with a great increment of the oxidation peak current on the CILE, which was due to the presence of ionic liquid in the modified electrode adsorbed the guanosine on the surface and promoted the electrochemical response. The electrochemical parameters such as the electron transfer coefficient (α), the electron transfer number (n), and the electrode reaction standard rate constant (k_s) were calculated as 0.74, 1.9 and 1.26 × 10⁻⁴ s⁻¹, respectively. Under the optimal conditions the oxidation peak current showed a good linear relationship with the guanosine concentration in the range from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol/L by cyclic voltammetry with the detection limit of 2.61 × 10⁻⁷ mol/L (3σ). The common coexisting substances showed no interferences to the guanosine oxidation. The CILE showed good ability to distinguish the electrochemical response of guanosine and guanine in the mixture solution. The urine samples were further detected by the proposed method with satisfactory results.     

Biosensor based on laccase and an ionic liquid for determination of rosmarinic acid in plant extracts

Novel biosensors based on laccase from Aspergillus oryzae and the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIPF₆) and 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF₄) were constructed for determination of rosmarinic acid by square-wave voltammetry. The laccase catalyzes the oxidation of rosmarinic acid to the corresponding o-quinone, which is electrochemically reduced back to rosmarinic acid at +0.2 V vs. Ag/AgCl. The biosensor based on BMIPF₆ showed a better performance than that based on BMIBF₄. The best performance was obtained with 50:20:15:15% (w/w/w/w) of the graphite powder:laccase:Nujol:BMIPF₆ composition in 0.1 mol L⁻¹ acetate buffer solution (pH 5.0). The rosmarinic acid concentration was linear in the range of 9.99 × 10⁻⁷ to 6.54 × 10⁻⁵ mol L⁻¹ (r = 0.9996) with a detection limit of 1.88 × 10⁻⁷ mol L⁻¹. The recovery study for rosmarinic acid in plant extract samples gave values from 96.1 to 105.0% and the concentrations determined were in agreement with those obtained using capillary electrophoresis at the 95% confidence level. The BMIPF₆-biosensor demonstrated long-term stability (300 days; 920 determinations) and reproducibility, with a relative standard deviation of 0.56%.     

The use of silver nanoparticles as an effective modifier for the determination of arsenic and antimony by electrothermal atomic absorption spectrometry

Silver nanoparticles (AgNPs) were proposed as a new chemical modifier for the elimination of interferences when determining arsenic and antimony in aqueous NaCl or Na₂SO₄ solutions and in sea-water by electrothermal atomic absorption spectrometry. For this purpose, the AgNPs were prepared simply by reducing silver nitrate with sodium citrate. The effects of pyrolysis and atomization temperatures and the amounts of interferents and modifiers on the sensitivities of these elements were investigated. In the presence of the proposed modifier, a pyrolysis temperature of at least 1100 °C for arsenic and 900 °C for antimony could be applied without the loss of analytes, and the interferences were greatly reduced to allow for interference-free determination. The detection limits (N = 10, 3σ) for arsenic and antimony were 0.022 ng and 0.046 ng, respectively. AgNPs are cheaper and more available compared to many other modifiers. No background was detected, and the blank values were negligible.     

Direct electrochemistry of glucose oxidase entrapped in nano gold particles-ionic liquid-N,N-dimethylformamide composite film on glassy carbon electrode and glucose sensing

The direct electrochemistry of glucose oxidase (GOD) entrapped in nano gold particles (NAs)-N,N-dimethylformamide (DMF)-1-butyl-3-methylimidazolium hexafluophosphate (BMIMPF₆) composite film on a glassy carbon electrode (NAs-DMF-GOD (BMIMPF₆)/GC) has been investigated for first time. The immobilized GOD exhibits a pair of well-defined reversible peaks in 0.050 M pH 5 phosphate solutions (PS), resulting from the redox of flavin adenine dinucleotide (FAD) in GOD. The peak currents are three times as large as those of GOD-NAs-DMF film coated GC electrode (i.e. NAs-DMF-GOD (water)/GC). In addition, the NAs-DMF-GOD (BMIMPF₆) composite material has higher thermal stability than NAs-DMF-GOD (water). Results show that ionic liquid BMIMPF₆, DMF and NAs are requisite for GOD to exhibit a pair of stable and reversible peaks. Without any of them, the peaks of GOD become small and unstable. Upon the addition of glucose, the peak currents of GOD decrease and a new cathodic peak occurs at −0.8 V (versus SCE), which corresponds to the reduction of hydrogen peroxide (H₂O₂) generated by the catalytic oxidation of glucose. The peak current of the new cathodic peak and the glucose concentration show a linear relationship in the ranges of 1.0 × 10⁻⁷ to 1.0 × 10⁻⁶ M and 2.0 × 10⁻⁶ to 2.0 × 10⁻⁵ M. The kinetic parameter I_max of H₂O₂ is estimated to be 1.19 × 10⁻⁶ A and the apparent K_m (Michaelis-Menten constant) for the enzymatic reaction is 3.49 μM. This method has been successfully applied to the determination of glucose in human plasma and beer samples, and the average recoveries are 97.2% and 99%, respectively.     

Catalytic activity of iron hexacyanoosmate(II) towards hydrogen peroxide and nicotinamide adenine dinucleotide and its use in amperometric biosensors

Hydrogen peroxide and nicotinamide adenine dinucleotide (NADH) may be determined amperometrically using screen-printed electrodes chemically modified with iron(III) hexacyanoosmate(II) (Osmium purple) in flow injection analysis (FIA). The determination is based on the exploitation of catalytic currents resulting from the oxidation/reduction of the modifier. The performance of the sensor was characterized and optimized by controlling several operational parameters (applied potential, pH and flow rate of the phosphate buffer). Comparison has been made with analogous complexes of ruthenium (Ruthenium purple) and iron (Prussian blue). Taking into account the sensitivity and stability of corresponding sensors, the best results were obtained with the use of Osmium purple. The sensor exhibited a linear increase of the amperometric signal with the concentration of hydrogen peroxide in the range of 0.1-100 mg L⁻¹ with a detection limit (evaluated as 3σ) of 0.024 mg L⁻¹ with a R.S.D. 1.5% for 10 mg L⁻¹ H₂O₂ under optimized flow rate of 0.4 mL min⁻¹ in 0.1 M phosphate buffer carrier (pH 6) and a working potential of +0.15 V versus Ag/AgCl. Afterwards, a biological recognition element - either glucose oxidase or ethanol dehydrogenase - was incorporated to achieve a sensor facilitating the determination of glucose or ethanol, respectively. The glucose sensor gave linearity between current and concentration in the range from 1 to 250 mg L⁻¹ with a R.S.D. 2.4% for 100 mg L⁻¹ glucose, detection limit 0.02 mg L⁻¹ (3σ) and retained its original activity after 3 weeks when stored at 6 °C. Optimal parameters in the determination of ethanol were selected as: applied potential +0.45 V versus Ag/AgCl, flow rate 0.2 mL min⁻¹ in 0.1 M phosphate buffer carrier (pH 7). Different structural designs of the ethanol sensor were tested and linearity obtained was up to 1000 mg L⁻¹ with a maximum R.S.D. of 5.1%. Applications in food analysis were also examined.     

Oxidative condensation and chemiluminescence of 5-amino-2,3-dihydro-1,4-phtalazinedione

The oxidative condensation of (5-amino-2,3-dihydro-1,4-phtalazinedione) luminol was carried out under their oxidation by (NH₄)₂S₂O₈ and KIO₃ in the mixed water-organic (namely dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidinone (MPD)) solvent under the volume ratio 1:9. The structure of the products was studied by IR and Raman spectroscopy, elemental analysis and the derivatographic method. It was determined that oxidation by KIO₃ (E = 1.085 V) occurs on the amide nitrogen atoms, while in the case of (NH₄)₂S₂O₈ (E = 2.05 V) it occurs on the amino-group. The structure and thermal stability of the obtained products is determined by the nature of the oxidant. The active decomposition of luminol begins at t_d = 334.5 °C, while for the specimens of the polyluminols, which were synthesized in the water-DMSO and water-MPD mixtures, t_d equals 356.7 and 409.1 °C respectively. The worst thermal stability has products of luminol oxidation by KIO₃ (t_d = 282.5 °C). The mechanism of the luminol oxidative polymerization by (NH₄)₂S₂O₈ and KIO₃ has been proposed.     

Tetrazole derivatives and matrices as novel cobalamin coordinating compounds

Cobalamin (Cbl, vitamin B₁₂) consists of two moieties: (i) the corrin ring with the central Co-ion in the oxidation states Co^3+/2+/1+ and (ii) the nucleotide side chain. The lower position of the ring is typically occupied by the nucleotide base (Bzm), whereas the upper surface coordinates exchangeable ligands. We have found that amino-tetrazole can coordinate to H₂O · Cbl (Co³⁺) with K_d = 10⁻⁵-10⁻⁶ M. A specific group (presumably tetrazole, TZ) can be easily created in CNBr-activated Sepharose by treatment with . The prepared matrix (STZ) contained ≈10 mM of the active groups, which bound H₂O · corrinoids with K_d = 10⁻⁵-10⁻⁶ M. Stability of STZ-Cbl bonds gradually increased and reached K_d = 10⁻⁷ M over 10-20 h (20 °C, pH 6-7). This effect can be ascribed to partial displacement of Bzm and coordination of TZ to the lower position. The binding was most efficient at pH 4-7 and low ionic strength, yet, noticeable adsorption took place even at extreme conditions, pH 1-9 and I = 0-2 M. Reduced corrins (Co²⁺) also exhibited high affinity for STZ. The bound ligands could be eluted as H₂O · Cbl (pH 0), HO · Cbl (pH 14) or diCN · Cbl (pH 9-12, CN⁻). The adsorbent is applicable for one-step purification of corrins from a crude extract; separation of aquo- and diaquo-forms; specific capturing of H₂O · Cbl from a mixture containing organo-Cbls or protein-bound Cbl, analysis of peptide-Cbl dissociation kinetics, etc.     

Preparation and thermal properties of diglycidylether sulfone epoxy

A diglycidylether sulfone monomer (sulfone type epoxy monomer, SEP) was prepared from bis(4-hydroxyphenyl) sulfone (SDOL) and epichlorohydrin without any NaOH or KOH as basic catalyst. FT-IR, ¹H NMR, ¹³C NMR and mass spectroscopic instruments were utilized to determine the structure of the SEP monomer. The cured SEP epoxy material exhibited not only a higher T_g (163.81 °C) but also a higher T_g than pristine DGEBA (from 111.25 °C to 139.17 °C) when the SEP monomer moiety had been introduced into the DGEBA system. The thermal stability of cured epoxy herein was investigated by thermogravimetric analysis (TGA). The results demonstrated that the sulfone group of the cured SEP material decomposed at lower temperatures and formed thermally stable sulfate compounds, improving char yield and enhancing resistance against thermal oxidation. Additionally, the IPDT and char yield of the cured SEP epoxy (IPDT = 1455.75, char yield = 39.67%) exceeded those of conventional DGEBA epoxy (IPDT = 667.27, char yield = 16.25%).     

Gold nanoparticle–antibody conjugates for specific extraction and subsequent analysis by liquid chromatography–tandem mass spectrometry of malondialdehyde-modified low density lipoprotein as biomarker for cardiovascular risk

Oxidized low-density lipoproteins (OxLDLs) like malondialdehyde-modified low-density lipoprotein (MDA-LDL) play a major role in atherosclerosis and have been proposed as useful biomarkers for oxidative stress. In this study, gold-nanoparticles (GNPs) were functionalized via distinct chemistries with anti-MDA-LDL antibodies (Abs) for selective recognition and capture of MDA-LDL from biological matrices. The study focused on optimization of binding affinities and saturation capacities of the antiMDA-LDL-Ab-GNP bioconjugate by exploring distinct random and oriented immobilization approaches, such as (i) direct adsorptive attachment of Abs on the GNP surface, (ii) covalent bonding by amide coupling of Abs to carboxy-terminated-pegylated GNPs, (iii) oriented immobilization via oxidized carbohydrate moiety of the Ab on hydrazide-derivatized GNPs and (iv) cysteine-tagged protein A (cProtA)-bonded GNPs. Depending on immobilization chemistry, up to 3 antibodies per GNP could be immobilized as determined by ELISA. The highest binding capacity was achieved with the GNP-cProtA-Ab bioconjugate which yielded a saturation capacity of 2.24 ± 0.04 μg mL⁻¹ GNP suspension for MDA-LDL with an affinity K_d of 5.25 ± 0.11 × 10⁻¹⁰ M. The GNP-cProtA-antiMDA-LDL bioconjugate revealed high specificity for MDA-LDL over copper(II)-oxidized LDL as well as native human LDL. This clearly demonstrates the usefulness of the new GNP-Ab bioconjugates for specific extraction of MDA-LDL from plasma samples as biomarkers of oxidative stress. Their combination as specific immunoextraction nanomaterials with analysis by LC–MS/MS allows sensitive and selective detection of MDA-LDL in complex samples.