Home About us Contact
|
Home About us Contact | ||
|
|
||
Selective Detection (selective + detection)
Selected AbstractsDouble Modification of Electrode Surface for the Selective Detection of Epinephrine and Its Application to Flow Injection Amperometric AnalysisELECTROANALYSIS, Issue 22 2009Guang-Ri Xu Abstract A glassy carbon electrode having two polymer layers has been applied to selectively detect epinephrine. The inner layer formed by electropolymerization of macrocyclic nickel complex functioned as an electrocatalyst for epinephrine oxidation and the outer layer composed of hydrolyzed polyurethane ,-benzyl L -glutamate as a screening layer. Differential pulse voltammetry showed almost 100% recovery of epinephrine even in 100-fold excess of interferents. When applied to a dual glassy carbon electrode as an amperometric detector in flow injection analysis, a linear response over 0.1,,M and 10,,M was obtained. Recovery tested for 5-fold diluted human urine samples was 97.5%. [source] Alkanethiols Modified Gold Electrodes for Selective Detection of Molecules with Different Polarity and Molecular Size.ELECTROANALYSIS, Issue 3-5 2009Application to Vitamin B2 Analysis Abstract The cyclic voltammetry behavior of several molecules with different polarity and molecular size on gold electrodes modified with nonfunctionalized alkanethiols of different chain length, usually employed as chromatographic stationary phases, are studied. The redox systems hexacyanoferrate(II/III), ferrocene/ferrocine and hydroquinone/quinone are chosen as template molecules. As modifiers, ethanethiol, 1-octanethiol and di- n -octadecyldisulfide are selected. We can conclude that polar molecules can reach the electrode surface through channels created by the modifiers. However, when nonpolar compounds are analyzed, the nonpolar interactions between the analyte and the terminal group of the modifier lead to retention of the compound, retarding its arrival to the electrode surface. A molecule with polar and nonpolar part was used for the application of this conclusion. If the gold electrode is modified with di- n -octadecyldisulfide, the electrochemical behavior of vitamin B2 becomes simpler than that observed on a bare one. This result allows a sensitive and selective procedure to be developed for direct determination of vitamin B2 in pharmaceutical formulations. [source] Gold-Nanocluster-Based Fluorescent Sensors for Highly Sensitive and Selective Detection of Cyanide in WaterADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Yanlan Liu Abstract A novel, gold-nanocluster-based fluorescent sensor for cyanide in aqueous solution, which is based on the cyanide etching-induced fluorescence quenching of gold nanoclusters, is reported. In addition to offering high selectivity due to the unique Elsner reaction between cyanide and the gold atoms of gold nanoclusters, this facile, environmentally friendly and cost-effective method provides high sensitivity. With this sensor, the lowest concentration to quantify cyanide ions could be down to 200,×,10,9,M, which is approximately 14 times lower than the maximum level (2.7,×,10,6,M) of cyanide in drinking water permitted by the World Health Organization (WHO). Furthermore, several real water samples spiked with cyanide, including local groundwater, tap water, pond water, and lake water, are analyzed using the sensing system, and experimental results show that this fluorescent sensor exhibits excellent recoveries (over 93%). This gold-nanocluster-based fluorescent sensor could find applications in highly sensitive and selective detection of cyanide in food, soil, water, and biological samples. [source] Selective Detection of Trace Nitroaromatic, Nitramine, and Nitrate Ester Explosive Residues Using a Three-Step Fluorimetric Sensing Process: A Tandem Turn-off, Turn-on Sensor,JOURNAL OF FORENSIC SCIENCES, Issue 6 2007Jason C. Sanchez M.S. Abstract:, Detection of trace quantities of explosive residues plays a key role in military, civilian, and counter-terrorism applications. To advance explosives sensor technology, current methods will need to become cheaper and portable while maintaining sensitivity and selectivity. The detection of common explosives including trinitrotoluene (TNT), cyclotrimethylenetrinitramine, cyclotetramethylene-tetranitramine, pentaerythritol tetranitrate, 2,4,6-trinitrophenyl-N-methylnitramine, and trinitroglycerin may be carried out using a three-step process combining "turn-off" and "turn-on" fluorimetric sensing. This process first detects nitroaromatic explosives by their quenching of green luminescence of polymetalloles (,em , 400,510 nm). The second step places down a thin film of 2,3-diaminonaphthalene (DAN) while "erasing" the polymetallole luminescence. The final step completes the reaction of the nitramines and/or nitrate esters with DAN resulting in the formation of a blue luminescent traizole complex (,em = 450 nm) providing a "turn-on" response for nitramine and nitrate ester-based explosives. Detection limits as low as 2 ng are observed. Solid-state detection of production line explosives demonstrates the applicability of this method to real world situations. This method offers a sensitive and selective detection process for a diverse group of the most common high explosives used in military and terrorist applications today. [source] Selective Detection of Iron(III) by Rhodamine-Modified Fe3O4 Nanoparticles,ANGEWANDTE CHEMIE, Issue 27 2010Baodui Wang Rh-odins Meisterstück: Das Anknüpfen von N -(Rhodamin-6G)lactam-ethylendiamin an Fe3O4 -Nanopartikel über eine Polyethylenglycolkette macht die Rhodamineinheit besser wasserlöslich und geeignet für den empfindlichen und selektiven Nachweis von FeIII in Wasser im 2-ppb-Bereich. Diese Empfindlichkeit gilt auch in HeLa-Zellen, was auf mögliche Anwendungen dieser Nachweismethode in biologischen Systemen hinweist. [source] Use of Gold Nanoparticles in a Simple Colorimetric and Ultrasensitive Dynamic Light Scattering Assay: Selective Detection of Arsenic in Groundwater,ANGEWANDTE CHEMIE, Issue 51 2009Jhansi, Rani Kalluri Ganz wenig genügt: Der Gehalt von Arsen in Brunnenwasser in Bangladesh sowie in käuflichem Trinkwasser und in Leitungswasser im US-Staat Mississippi kann mithilfe eines Assays auf der Basis dynamischer Lichtstreuung (DLS) angezeigt werden. Die hochempfindliche und selektive colorimetrische Analyse (siehe Bild) weist Arsen in Konzentrationen von nur 3,ppt nach. [source] Selective Detection of Phosphotyrosine in the Presence of Various Phosphate-Containing Biomolecules with the Aid of a Terbium(III) ComplexCHEMBIOCHEM, Issue 11 2009Hiroki Akiba Finding phosphotyrosine: Phosphotyrosine (either in its monomeric form or as a component of oligopeptides) was selectively detected by using luminescence in the presence of a specialized terbium(III) complex, without any signals from nonphosphorylated tyrosine, phosphoserine, phosphothreonine, nucleotides, or nucleic acids. Tyrosine phosphorylation could clearly be distinguished even in the presence of single-stranded RNA. [source] ChemInform Abstract: A Red-Emitting Naphthofluorescein-Based Fluorescent Probe for Selective Detection of Hydrogen Peroxide in Living CellsCHEMINFORM, Issue 13 2009Aaron E. Albers Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Dipyrrolyl-Functionalized Bipyridine-Based Anion Receptors for Emission-Based Selective Detection of Dihydrogen PhosphateCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2007Patrick Plitt Dr. Abstract New cationic anion receptors, based on the use of pyrrole-substituted bipyridine and coordinated to transition metals, are described. Specifically, polypyridine,ruthenium and ,rhodium cores have been functionalized to generate an anion binding site. The design was chosen to probe the influence of the pyrrole-to-pyrrole separation on anion-binding affinities and selectivities; this distance is greater in the new systems of this report (receptors 1 and 2) relative to that present in related dipyrrolyl quinoxaline based receptors 3 and 4. Solution-phase anion-binding studies, carried out by means of 1H,NMR spectroscopic titrations in [D6]DMSO and isothermal titration calorimetry (ITC) in DMSO, reveal that 1 and 2 bind most simple anions with substantially higher affinity than either 3 or 4. In the case of chloride anion, structural studies, carried out by means of single-crystal X-ray diffraction analyses, are consistent with the solution-phase results and reveal that receptors 1 and 2 are both able to stabilize complexes with this halide anion in the solid state. [source] A Dual-Electrode Approach for Highly Selective Detection of Glucose Based on Diffusion Layer Theory: Experiments and SimulationCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2005Kang Wang Dr. Abstract A dual-electrode configuration for the highly selective detection of glucose in the diffusion layer of the substrate electrode is presented. In this approach, a glassy carbon electrode (GCE, substrate) modified with a conductive layer of glucose oxidase/Nafion/graphite (GNG) was used to create an interference-free region in its diffusion layer by electrochemical depletion of interfering electroactive species. A Pt microelectrode (tip, 5 ,m in radius) was located in the diffusion layer of the GNG-modified GCE (GNG-G) with the help of scanning electrochemical microscopy. Consequently, the tip of the electrode could sense glucose selectively by detecting the amount of hydrogen peroxide (H2O2) formed from the oxidization of glucose on the glucose oxidase layer. The influences of parameters, including tip,substrate distance, substrate potential, and electrolyzing time, on the interference-removing efficiency of this dual-electrode approach have been investigated systematically. When the electrolyzing time was 30 s, the tip,substrate distance was 1.8,a (9.0 ,m) (where a is the radius of the tip electrode), the potentials of the tip and substrate electrodes were 0.7 V and 0.4 V, respectively, and a mixture of ascorbic acid (0.3,mM), uric acid (0.3,mM), and 4-acetaminophen (0.3,mM) had no influence on the glucose detection. In addition, the current,time responses of the tip electrode at different tip,substrate distances in a solution containing interfering species were numerically simulated. The results from the simulation are in good agreement with the experimental data. This research provides a concept of detection in the diffusion layer of a substrate electrode, as an interference-free region, for developing novel microelectrochemical devices. [source] Flow Injection Analysis of Sulfide Using a Cinder/Tetracyano Nikelate Modified Screen-Printed ElectrodeELECTROANALYSIS, Issue 9 2005Jyh-Myng Zen Abstract Flow injection analysis (FIA) of sulfide is presented using a screen-printed carbon electrode modified with a cinder/tetracyano nickelate hybrid (designated as cinder/NiTcSPE). Hybridization of NiTc was achieved in iron-enriched industrial waste cinder material through the bimetallic formation of FeIII[NiII(CN)4]. The electrocatalytic oxidation of sulfide is mediated by the higher oxidation state of Ni in this hybrid-bimetallic complex. The system shows a detection limit (S/N=3) of 0.06,,M and a linear working range up to 1,mM in pH,10, 0.1,M KCl solution. Taking into account the relatively low volatility of the analyte in alkaline conditions, the system is ideally suited for the accurate detection of sulfide. The response of the electrode to sulfide is highly reproducible, thereby offering the potential development of a disposable amperometric sensor for sulfide. Selective detection of sulfide in cigarette smoke is presented in this study as an example of a real sample application. [source] Selective detection of superoxide anion radicals generated from macrophages by using a novel fluorescent probeFEBS JOURNAL, Issue 7 2007Jing Jing Gao Quantitation of superoxide radical (O,2,·) production at the site of radical generation remains challenging. A simple method to detect nanomolar to micromolar levels of superoxide radical in aqueous solution has been developed and optimized. This method is based on the efficient trapping of O2,· using a novel fluorescent probe (2-chloro-1,3-dibenzothiazolinecyclohexene), coupled with a spectra character-signaling increase event. A high-specificity and high-sensitivity fluorescent probe was synthesized in-house and used to image O2,· in living cells. Better selectivity for O2,· over competing cellular reactive oxygen species and some biological compounds illustrates the advantages of our method. Under optimal conditions, the linear calibration range for superoxide anion radicals was 5.03 × 10,9,3.33 × 10,6 m. The detection limit was 1.68 × 10,9 m. Fluorescence images of probe-stained macrophages stimulated with 4,-phorbol 12-myristate 13-acetate were obtained successfully using a confocal laser scanning microscope. [source] Catalytic Voltammetric Determination of Cladribine in Biological SamplesELECTROANALYSIS, Issue 5-6 2003Noemí de-los-Santos-Álvarez Abstract An electrochemical method for the citotoxic prodrug cladribine determination is proposed. Graphite electrodes modified with cladribine showed a redox process with a formal potential of 0.173,V at pH 6, after the oxidation of the adenine moiety of the drug, whose current can be employed as analytical signal with a detection limit of 75,nM by square-wave voltammetry. As these oxidation products exhibit great electrocatalytic activity toward the electro-oxidation of NADH at low potentials, the analytical response can further be amplified. As a result, the detection limit was improved up to 1,nM using differential pulse voltammetry. The method was applied to the determination of cladribine in serum and urine samples after solid-phase extraction. No electroactive interferences were found in both fluids. The method allows the selective detection of the drug in the presence of the main metabolite, 2-chloroadenosine, which is not able to electrocatalize the NADH oxidation. [source] Permeation of tetracyclines through membranes of liposomes and Escherichia coliFEBS JOURNAL, Issue 2 2000Albrecht Sigler Uptake of tetracycline (tc), 2-tetracyclinonitrile (CN-tc), and 9-(N,N -dimethylglycylamido)-6-demethyl-6-deoxytetracycline (DMG-DMDOT) by liposomes containing Tet repressor (TetR) and by Escherichia coli cells overexpressing TetR was examined. TetR specifically binds to tetracyclines, enhances their fluorescence and thereby allows selective detection of tetracyclines that have crossed the membranes. Analysis of the diffusion of tc and DMG-DMDOT into liposomes yielded permeation coefficients of (2.4 ± 0.6) × 10,9 cm·s,1 and (3.3 ± 0.8) × 10,9 cm·s,1, respectively. Similar coefficients were obtained for uptake of these tetracyclines by E. coli, indicating that diffusion through the cytoplasmic membrane is the rate-limiting step. The permeation coefficients translate into half-equilibration times of approximately 35 ± 15 min and explain how efflux pumps can mediate resistance against tetracyclines. Furthermore, diffusion of CN-tc into liposomes was at least 400-fold slower than that of tc, indicating that the carboxamide group at position C2 is required for efficient permeation of tc through lipid membranes and thereby explaining the lack of antibiotic activity of CN-tc. [source] Gold-Nanocluster-Based Fluorescent Sensors for Highly Sensitive and Selective Detection of Cyanide in WaterADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Yanlan Liu Abstract A novel, gold-nanocluster-based fluorescent sensor for cyanide in aqueous solution, which is based on the cyanide etching-induced fluorescence quenching of gold nanoclusters, is reported. In addition to offering high selectivity due to the unique Elsner reaction between cyanide and the gold atoms of gold nanoclusters, this facile, environmentally friendly and cost-effective method provides high sensitivity. With this sensor, the lowest concentration to quantify cyanide ions could be down to 200,×,10,9,M, which is approximately 14 times lower than the maximum level (2.7,×,10,6,M) of cyanide in drinking water permitted by the World Health Organization (WHO). Furthermore, several real water samples spiked with cyanide, including local groundwater, tap water, pond water, and lake water, are analyzed using the sensing system, and experimental results show that this fluorescent sensor exhibits excellent recoveries (over 93%). This gold-nanocluster-based fluorescent sensor could find applications in highly sensitive and selective detection of cyanide in food, soil, water, and biological samples. [source] A Graphene Nanoprobe for Rapid, Sensitive, and Multicolor Fluorescent DNA AnalysisADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Shijiang He Abstract Coupling nanomaterials with biomolecular recognition events represents a new direction in nanotechnology toward the development of novel molecular diagnostic tools. Here a graphene oxide (GO)-based multicolor fluorescent DNA nanoprobe that allows rapid, sensitive, and selective detection of DNA targets in homogeneous solution by exploiting interactions between GO and DNA molecules is reported. Because of the extraordinarily high quenching efficiency of GO, the fluorescent ssDNA probe exhibits minimal background fluorescence, while strong emission is observed when it forms a double helix with the specific targets, leading to a high signal-to-background ratio. Importantly, the large planar surface of GO allows simultaneous quenching of multiple DNA probes labeled with different dyes, leading to a multicolor sensor for the detection of multiple DNA targets in the same solution. It is also demonstrated that this GO-based sensing platform is suitable for the detection of a range of analytes when complemented with the use of functional DNA structures. [source] Synthesis of Indium and Indium Oxide Nanoparticles from Indium Cyclopentadienyl Precursor and Their Application for Gas Sensing,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2003K. Soulantica Abstract Decomposition of the organometallic precursor [In(,5 -C5H5)] in toluene in the presence of methanol (8 vol.-%) at room temperature leads to the immediate formation of aggregates of indium nanoparticles of 15,±,2 nm mean diameter. The aggregates are roughly spherical with a mean size of 400,±,40 nm. The particles were characterized by means of transmission electron and high-resolution transmission electron microscopies (TEM and HRTEM), and X-ray diffraction (XRD) studies indicate that the powder consists of the tetragonal phase of indium. The thermal oxidation in air of these nanoparticles yields well-crystallized nanoparticles of In2O3 with unchanged morphology (aggregates of nanoparticles of 16.6,±,2 nm mean diameter with aggregate mean size of 400,±,40 nm) and without any sign of coalescence. XRD pattern shows that the powder consists of the cubic phase of In2O3. The electrical conductivity measurements demonstrate that this material is highly sensitive to an oxidizing gas such as nitrogen dioxide and barely sensitive to a reducing gas such as carbon monoxide. Its association with SnO2 -based sensors allows the selective detection of carbon monoxide (30 ppm) and sub-ppm amounts of nitrogen dioxide (400 ppb) in a mixture at 21,°C and at a relative humidity of 60,%. [source] Shock tube pyrolysis of thiopheneINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2003Hafeez Ur Rahman Memon Abstract The kinetics of the thermal decomposition of thiophene diluted in argon have been studied behind reflected shock waves in a single pulse shock tube over the temperature range 1598,2022 K and pressures between 2.5 and 3.44 bar. Product yields and composition were determined using capillary column gas chromatography with flame ionization detection and flame photometric sulphur selective detection. The principal hydrocarbon product at all temperatures was ethyne. Ethanethiol was found to be the major sulphur product together with H2S formed in significant concentrations at lower temperatures. Carbon disulphide was also formed at higher temperatures. Additional reaction products were CH4, C2H4, C3H4, C4H3, C4H6, C4H4, C6H6 and C4H2 with some traces were found of C5 and C6H5 species. It was concluded that pyrolysis of thiophene is initiated by C,S bond fission to form the C4H4S radical which reacts to give C4H3 + SH together with the reaction giving C3H4 + CS. The rate expression obtained for the pyrolysis reaction was k (C4H4S)=2.2×1011 exp (270 kJ mol,1) s,1. Copyright © 2002 John Wiley & Sons, Ltd. [source] Influence of the metabolic properties of human cells on the kinetic of formation of the major benzo[a]pyrene DNA adductsJOURNAL OF APPLIED TOXICOLOGY, Issue 5 2008Caroline Marie Abstract Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants. Some of them, including benzo[a]pyrene (B[a]P), are tumorigenic due to their ability to generate DNA adducts. In order to define potential biomarkers of B[a]P exposure, the aim of the study was to identify the major stable DNA adducts in B[a]P-treated human cells. The role played by cellular metabolism on the nature and frequency of the DNA lesions was investigated using keratinocytes (HaCat) and actively metabolizing hepatocytes (HepG2) cell lines. Quantification of DNA damage was carried out by HPLC coupled to tandem mass spectrometry, a sensitive method making possible the selective detection of the different potential stable DNA adducts of B[a]P. These include two adducts of the 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) pathway and three adducts of the radical cation pathway. The results indicate that incubation of cells with B[a]P induces almost exclusively the formation of BPDE DNA adducts on purine bases. The amount of DNA adducts generated in hepatocytes was found to be two orders of magnitude higher than that measured in keratinocytes. Interestingly, the level of the DNA adducts produced in the cells incubated with (±)- anti -BPDE was similar in the two cell lines, indicating that the difference observed upon incubation with B[a]P could be attributed to different kinetics of B[a]P metabolism. The repair rate of BPDE DNA adducts was identical in the two cell lines with a half-life estimated to be around 20 h. These data support the use of the stable BPDE DNA adducts, as relevant biomarkers of exposure to B[a]P. Copyright © 2007 John Wiley & Sons, Ltd. [source] Investigation of tyrosine nitration in proteins by mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2001Ann-Sofi Petersson Abstract In vivo nitration of tyrosine residues is a post-translational modification mediated by peroxynitrite that may be involved in a number of diseases. The aim of this study was to evaluate possibilities for site-specific detection of tyrosine nitration by mass spectrometry. Angiotensin II and bovine serum albumin (BSA) nitrated with tetranitromethane (TNM) were used as model compounds. Three strategies were investigated: (i) analysis of single peptides and protein digests by matrix-assisted laser desorption/ionization (MALDI) peptide mass mapping, (ii) peptide mass mapping by electrospray ionization (ESI) mass spectrometry and (iii) screening for nitration by selective detection of the immonium ion of nitrotyrosine by precursor ion scanning with subsequent sequencing of the modified peptides. The MALDI time-of-flight mass spectrum of nitrated angiotensin II showed an unexpected prompt fragmentation involving the nitro group, in contrast to ESI-MS, where no fragmentation of nitrated angiotensin II was observed. The ESI mass spectra showed that mono- and dinitrated angiotensin II were obtained after treatment with TNM. ESI-MS/MS revealed that the mononitrated angiotensin II was nitrated on the side-chain of tyrosine. The dinitrated angiotensin II contained two nitro groups on the tyrosine residue. Nitration of BSA was confirmed by Western blotting with an antibody against nitrotyrosine and the sites for nitration were investigated by peptide mass mapping after in-gel digestion. Direct mass mapping by ESI revealed that two peptides were nitrated. Precursor ion scanning for the immonium ion for nitrotyrosine revealed two additional partially nitrated peptides. Based on the studies with the two model compounds, we suggest that the investigation of in vivo nitration of tyrosine and identification of nitrated peptides might be performed by precursor ion scanning for the specific immonium ion at m/z 181.06 combined with ESI-MS/MS for identification of the specific nitration sites. Copyright © 2001 John Wiley & Sons, Ltd. [source] Surface-enhanced Raman sensors: early history and the development of sensors for quantitative biowarfare agent and glucose detectionJOURNAL OF RAMAN SPECTROSCOPY, Issue 6-7 2005Christy L. Haynes Abstract Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for the sensitive and selective detection of low-concentration analytes. This paper includes a discussion of the early history of SERS, the concepts that must be appreciated to optimize the intensity of SERS and the development of SERS-based sensors. In order to achieve the lowest limits of detection, both the relationship between surface nanostructure and laser excitation wavelength, as well as the analyte/surface binding chemistry, must be carefully optimized. This work exploits the highly tunable nature of nanoparticle optical properties to establish the first set of optimization conditions. The SERS enhancement factor, EFSERS, is optimized when the energy of the localized surface plasmon resonance (LSPR) lies between the energy of the excitation wavelength and the energy of the vibrational band of interest. With the narrow LSPRs used in this work, it is straightforward to achieve EFSERS , 108. These optimization conditions were exploited to develop SERS-based sensors for two important target molecules: a Bacillus anthracis biomarker and glucose in a serum protein mixture. Using these optimized film-over-nanosphere surfaces, an inexpensive, portable Raman spectrometer was used successfully to detect the infectious dose of Bacillus subtilis spores with only a 5-s data collection. The biomarker used to detect the Bacillus subtilis spores binds irreversibly to SERS substrates, whereas other important biomolecules, such as glucose, do not have any measurable binding affinity to a bare silver surface. To overcome this difficulty, a biocompatible partition layer was self-assembled on the SERS substrate before exposure to the analyte solution. Using the partition layer approach to concentrate glucose near the SERS-active substrate, physiological glucose concentrations can be detected even in the presence of interfering serum proteins. Copyright © 2005 John Wiley & Sons, Ltd. [source] Toward direct mapping of neuronal activity: MRI detection of ultraweak, transient magnetic field changes,MAGNETIC RESONANCE IN MEDICINE, Issue 6 2002Jerzy Bodurka Abstract A novel method based on selective detection of rapidly changing ,B0 magnetic fields and suppression of slowly changing ,B0 fields is presented. The ultimate goal of this work is to present a method that may allow detection of transient and subtle changes in B0 in cortical tissue associated with electrical currents produced by neuronal activity. The method involves the detection of NMR phase changes that occur during a single-shot spin-echo (SE) echo-planar sequence (EPI) echo time. SE EPI effectively rephases all changes in B0 that occur on a time scale longer than the echo time (TE) and amplifies all ,B0 changes that occur during TE/2. The method was tested on a phantom that contains wires in which current can be modulated. The sensitivity and flexibility of the technique was demonstrated by modulation of the temporal position and duration of the stimuli-evoked transient magnetic field relative to the 180 RF pulse in the imaging sequence,requiring precise stimulus timing. Currently, with this method magnetic field changes as small as 2 × 10,10 T (200 pT) and lasting for 40 msec can be detected. Implications for direct mapping of brain neuronal activity with MRI are discussed. Magn Reson Med 47:1052,1058, 2002. Published 2002 Wiley-Liss, Inc. [source] Polyphenolic composition of roots and petioles of Rheum rhaponticum L.PHYTOCHEMICAL ANALYSIS, Issue 2 2009Tõnu Püssa Abstract Introduction Various species of the genus Rheum (Polygonaceae) are known for their high content of medicinally important hydroxyanthraquinones. However, little information is available concerning the polyphenolic composition of garden or dietary rhubarb Rheum rhaponticum L. (R. rhaponticum). Objective Determination of further polyphenols in the roots and petioles of R. rhaponticum. Methodology The dried plant material was extracted with 10-fold excess (v/w) of methanol and subsequently diluted five times with methanol,water (1:1) and analysed by reversed-phase liquid chromatography using tandem UV-photodiode array and mass selective detection (RP-HPLC-UV-ESI/MS2). Polyphenols were identified using either HPLC-ESI/MS2 data obtained for respective commercial standards or by comparison of a parent ion fragmentation picture with the respective MS2 spectrum from the literature. Results The roots of R. rhaponticum were very rich in various hydroxystilbenes and contained four main substance groups ,derivatives of trans -piceatannol, trans -resveratrol, trans -rhapontigenin and trans -deoxyrhapontigenin. Additionally, pterostilbene acetylglucosides and a number of hydroxyanthraquinones and their glycosides were identified in the root samples. The profile of polyphenols in the petioles of R. rhaponticum was similar to that of the roots but the content of individual substances was remarkably lower. The petioles of the R. rhaponticum additionally contained significant amounts of derivatives of flavonol quercetin, which is a good antioxidant. Conclusion The study has shown that roots of R. rhaponticum contain a wide variety of hydroxystilbenes and deserve further consideration as a source of medicinally interesting compounds. Copyright © 2008 John Wiley & Sons, Ltd. [source] Quantitative analyses of indoloquinazoline alkaloids in Fructus Evodiae by high-performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2006Yan Zhou Fructus Evodiae (Wuzhuyu), the fruits of Evodia rutaecarpa and related varieties, is widely used in traditional Chinese medicine. The bioactive constituents include the indoloquinazoline alkaloids rutaecarpine, evodiamine and dehydroevodiamine. A new assay based on high-performance liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry (HPLC/UV/APCI-MS/MS) was developed for the measurement of the indoloquinazoline alkaloids in commercial Fructus Evodiae products. Initially, the MS/MS fragmentation pathways of indoloquinazoline alkaloids were investigated to identify fragment ions that might be useful for the sensitive and selective detection of trace indoloquinazoline alkaloids during LC/MS/MS. Then, quantitative MS analysis of five indoloquinazoline alkaloids in 12 commercial Fructus Evodiae products from different geographical sources was performed. Analyte recovery was in the range of 97.5,105.3% for all with relative standard deviations (RSDs) below 6%, the intra-assay and inter-assay RSDs were less than 7%, and good linear relationships were shown with correlation coefficients for the analytes exceeding 0.999. Therefore, this LC/MS/MS assay facilitated the rapid quantitative analysis of rutaecarpine, evodiamine, evodiamide, 14-formyldihydrorutaecarpine and dehydroevodiamine in 12 commercial Fructus Evodiae products with excellent recovery, repeatability, accuracy and sensitivity. This method is simple and specific and can be used for identification and quality control of this traditional Chinese remedy. Copyright © 2006 John Wiley & Sons, Ltd. [source] Determination of perfluorooctane sulfonate in river water by liquid chromatography/atmospheric pressure photoionization mass spectrometry by automated on-line extraction using turbulent flow chromatographyRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2003Masahiko Takino A simple, fast and sensitive liquid chromatography/atmospheric pressure photoionization mass spectrometry (LC/APPI-MS) method, with automated on-line extraction using turbulent flow chromatography (TFC), was developed for the determination of perfluorooctane sulfonate (PFOS) in river water. In this method, following an on-line extraction by injection onto a column under TFC conditions, PFOS is back-flushed onto a reversed-phase column via on-line column switching, and resolved chromatographically at a laminar flow rate of 1,mL min,1. Using this tandem LC-LC/APPI-MS system the extraction, separation and selective detection of PFOS in river water could be achieved with satisfactory selectivity and sensitivity. The limit of detection (LOD) (S/N,=,3) and the limit of quantitation (LOQ) (S/N,=,10)were 5.35 and 17.86,pg,mL,1. The described procedure was very simple since no off-line sample preparation was required, total analysis time being 18.75,min. Copyright © 2003 John Wiley & Sons, Ltd. [source] A Highly Selective FRET-Based Fluorescent Probe for Detection of Cysteine and HomocysteineCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2010Hoi-Yan Shiu Fluorescent probe: A "turn-on" FRET-based fluorescent probe for selective detection of cysteine (Cys) and homocysteine (Hcy) under physiological conditions was synthesised (see figure). The probe features excellent selectivity, fast response times and good linearity towards Cys and Hcy detection. [source] A Dual-Electrode Approach for Highly Selective Detection of Glucose Based on Diffusion Layer Theory: Experiments and SimulationCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2005Kang Wang Dr. Abstract A dual-electrode configuration for the highly selective detection of glucose in the diffusion layer of the substrate electrode is presented. In this approach, a glassy carbon electrode (GCE, substrate) modified with a conductive layer of glucose oxidase/Nafion/graphite (GNG) was used to create an interference-free region in its diffusion layer by electrochemical depletion of interfering electroactive species. A Pt microelectrode (tip, 5 ,m in radius) was located in the diffusion layer of the GNG-modified GCE (GNG-G) with the help of scanning electrochemical microscopy. Consequently, the tip of the electrode could sense glucose selectively by detecting the amount of hydrogen peroxide (H2O2) formed from the oxidization of glucose on the glucose oxidase layer. The influences of parameters, including tip,substrate distance, substrate potential, and electrolyzing time, on the interference-removing efficiency of this dual-electrode approach have been investigated systematically. When the electrolyzing time was 30 s, the tip,substrate distance was 1.8,a (9.0 ,m) (where a is the radius of the tip electrode), the potentials of the tip and substrate electrodes were 0.7 V and 0.4 V, respectively, and a mixture of ascorbic acid (0.3,mM), uric acid (0.3,mM), and 4-acetaminophen (0.3,mM) had no influence on the glucose detection. In addition, the current,time responses of the tip electrode at different tip,substrate distances in a solution containing interfering species were numerically simulated. The results from the simulation are in good agreement with the experimental data. This research provides a concept of detection in the diffusion layer of a substrate electrode, as an interference-free region, for developing novel microelectrochemical devices. [source] SERS Microscopy: Nanoparticle Probes and Biomedical ApplicationsCHEMPHYSCHEM, Issue 9-10 2009Sebastian Schlücker Prof. Abstract Microspectroscopic imaging: Surface-enhanced Raman scattering (SERS) microscopy is a novel method of vibrational microspectroscopic imaging for the selective detection of biomolecules in targeted research. This review summarizes current designs of nanoparticle-based SERS probes (see figure) and highlights first biomedical applications of SERS microscopy for protein localization ex and in vivo. Surface-enhanced Raman scattering (SERS) microscopy is a novel method of vibrational microspectroscopic imaging for the selective detection of biomolecules in targeted research. This technique combines the advantages of biofunctionalized metal nanoparticles and Raman microspectroscopy for visualizing and quantifying the distribution of target molecules such as proteins in cells and tissues. Advantages of SERS over existing labeling approaches include the tremendous multiplexing capacity, quantification using the characteristic SERS signatures and high photostability. This review summarizes current designs of nanoparticle-based SERS probes and highlights first biomedical applications of SERS microscopy for protein localization ex and in vivo. [source] Highly selective single nucleotide polymorphism recogniton by a chiral (5S) PNA beacon,CHIRALITY, Issue 1 2009Filbert Totsingan Abstract A chiral peptide nucleic acid (PNA) beacon containing a C-5 modified monomer based on L-lysine was synthesized. The terminal amino group of the lysine side chain was linked to a spacer for future applications on surfaces. The PNA beacon bears a carboxyfluorescein fluorophore and a dabcyl quencher at opposite ends. The DNA binding properties were compared with those of a homologous PNA beacon containing only achiral monomers. Both beacons underwent a fluorescence increase in the presence of complementary DNA, with higher efficiency and higher selectivity (evaluated using single mismatched DNA sequences) observed for the chiral monomer containing PNA. Ion exchange (IE) HPLC with fluorimetric detection was used in combination with the beacon for the selective detection of complementary DNA. A fluorescent peak corresponding to the PNA beacon:DNA duplex was observed at a very low detection limit (1 nM). The discriminating capacity of the chiral PNA beacon for a single mismatch was found to be superior to those observed with the unmodified one, thus confirming the potency of chirality for increasing the affinity and specificity of DNA recognition. Chirality, 2009. © 2008 Wiley-Liss, Inc. [source] Chlorin,Bacteriochlorin Energy-transfer Dyads as Prototypes for Near-infrared Molecular Imaging Probes: Controlling Charge-transfer and Fluorescence Properties in Polar MediaPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Hooi Ling Kee The photophysical properties of two energy-transfer dyads that are potential candidates for near-infrared (NIR) imaging probes are investigated as a function of solvent polarity. The dyads (FbC-FbB and ZnC-FbB) contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. The dyads were studied in toluene, chlorobenzene, 1,2-dichlorobenzene, acetone, acetonitrile and dimethylsulfoxide (DMSO). In both dyads, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of ,(5,10 ps),1 and a yield of >99% in nonpolar and polar media. In toluene, the fluorescence yields (,f = 0.19) and singlet excited-state lifetimes (,,5.5 ns) are comparable to those of the benchmark bacteriochlorin. The fluorescence yield and excited-state lifetime decrease as the solvent polarity increases, with quenching by intramolecular electron (or hole) transfer being greater for FbC-FbB than for ZnC-FbB in a given solvent. For example, the ,f and , values for FbC-FbB in acetone are 0.055 and 1.5 ns and in DMSO are 0.019 and 0.28 ns, whereas those for ZnC-FbB in acetone are 0.12 and 4.5 ns and in DMSO are 0.072 and 2.4 ns. The difference in fluorescence properties of the two dyads in a given polar solvent is due to the relative energies of the lowest energy charge-transfer states, as assessed by ground-state redox potentials and supported by molecular-orbital energies derived from density functional theory calculations. Controlling the extent of excited-state quenching in polar media will allow the favorable photophysical properties of the chlorin,bacteriochlorin dyads to be exploited in vivo. These properties include very large Stokes shifts (85 nm for FbC-FbB, 110 nm for ZnC-FbB) between the red-region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (,f = 760 nm), long bacteriochlorin excited-state lifetime (,5.5 ns), and narrow (,20 nm) absorption and fluorescence bands. The latter will facilitate selective excitation/detection and multiprobe applications using both intensity- and lifetime-imaging techniques. [source] | |||||||||||||||||||||||||