Comparison of three different configurations of dual ultramicroelectrodes for the decomposition of S-Nitroso-L-glutathione and the direct detection of nitric oxide

Podoplanin (PDP) is a small transmembrane protein and widely present in various specialized cells throughout the human body. It is a specific marker for identification of lymphatic vessel and a candidate marker for cancer stem cells in squamous cell carcinoma of the lung. We report on method for the highly selective determination of PDP by using a surface plasmon resonance imaging (SPRI) that exploits the highly selective interaction between PDP and anti-human PDP monoclonal antibody (IgG). The sensor has a dynamic range between 0.25 and 1.0?ng?mL^?1, and a detection limit of 15?pg?mL^?1. It was applied to the determination of PDP in blood plasma and tissue homogenates from paired normal and lung tumor tissue.

Analysis of dextromethorphan and pseudoephedrine in human plasma and urine samples using hollow fiber-based liquid–liquid–liquid microextraction and corona discharge ion mobility spectrometry

We report on the use of hollow fiber liquid-liquid-liquid microextraction (HF-LLLME) followed by corona discharge ion mobility spectrometry for the determination of dextromethorphan and pseudoephedrine in urine and plasma samples. The effects of pH of the donor phase, stirring rate, ionic strength and extraction time on HF-LLLME were optimized. Under the optimized conditions, the linear range of the calibration curves for dextromethorphan in plasma and urine, respectively, are from 1.5 to 150 and from 1 to 100 ng mL^?1. The ranges for pseudoephedrine, in turn, are from 30 to 300 and from 20 to 200 ng mL^?1. Correlation coefficients are better than 0.9903. The limits of detection are 0.6 and 0.3 ng mL^?1 for dextromethorphan, and 8.6 and 4.2 ng mL^?1 for pseudoephedrine in plasma and urine samples, respectively. The relative standard deviations range from 6 to 8%.

Micro-solid phase extraction of ochratoxin A, and its determination in urine using capillary electrophoresis

We describe a simple, environmentally friendly and selective technique for the determination of ochratoxin A (OTA) in urine. It involves (a) the use of a molecularly imprinted polymer as a sorbent in micro-solid-phase extraction in which the sorbent is contained in a propylene membrane envelope, and (b) separation and detection by capillary electrophoresis (CE). Under optimized conditions, response is linear in the range between 50 and 300 ng mL^?1 (with a correlation coefficient of 0.9989), relative standard deviations range from 4 to 8 %, the detection limit for OTA in urine is 11.2 ng mL^?1 (with a quantification limits of 32.5 ng mL^?1) which is lower than those of previously reported methods for solid-phase extraction combined with CE. The recoveries of OTA from urine spiked at levels of 50, 150 and 300 ng mL^?1 ranged from 93 to 97 %.

Chemiluminescent determination of the activity of caspase-3 using a specific peptide substrate and magnetic beads

We report on a new scheme for the determination of the activity of caspase-3 using a specific peptide labeled with N-(4-aminobutyl)-N-ethylisoluminol (ABEI) as a chemiluminescent (CL) probe and on the development of magnetic separation technology. Firstly, the ABEI-labeled and biotinylated peptide was prepared and conjugated to streptavidin-coated magnetic beads (MBs) to form f-MBs (functionalized magnetic beads). The f-MBs contain a site (DEVD, Asp-Glu-Val-Asp) that is cleaved by caspase-3. Upon cleavage, the terminal residue attached to ABEI can dissociate from the f-MBs and can be used for CL detection. CL intensity is linearly related to the concentration of caspase-3 in the range 1.0 to 600 ng mL^?1, with a detection limit of 0.3 ng mL^?1. The relative standard deviation of the assay is 3.6 % at a level of 50 ng mL^?1 of caspase-3 (for n?=?11). The CL assay has been applied to the determination of caspase-3 in Jurkat cell extract with recoveries between 96.6 % and 106.1 % (n?=?5).

Sorption of platinum on immobilized microorganisms for its on-line preconcentration and chemiluminescent determination in water samples

Fungi of the type Aspergillus sp. were immobilized on a cellulosic resin and used as a biosorbent for the on-line preconcentration and separation of Pt(IV) ions prior to their chemiluminescent determination via flow injection analysis. Biosorption and elution conditions were optimized, and the results compared to biosorbents based on the use of Chlorella vulgaris algae and Saccharomyces cerevisiae yeast in terms of preconcentration and selective retention of Pt(IV). The immobilized fungi presented here have a high potential for use in platinum biosorption. The procedure exhibits the currently lowest limit of detection (0.02 ng mL^?1 of Pt) and very high selectivity. The procedure was applied to the determination of Pt(IV) in river water, road run-off, and wastewater samples.

Voltammetric sensing of thallium at a carbon paste electrode modified with a crown ether

We describe a new method for differential-pulse anodic stripping voltammetric determination of thallium(I) using a carbon paste electrode modified with dicyclohexyl-18-crown-6. The effect of supporting electrolyte (type and pH), accumulation and reduction potential, and of time and amount of modifier were investigated by differential pulse anodic stripping voltammetry. A method was then worked out for the determination of thallium at low levels. Under optimized conditions, the response to Tl(I) is linear in the range from 3.0 to 250 ng mL^?1. The detection limit is 0.86 ng mL^?1. The sensor displays good repeatability (with a relative standard deviation of ±2.70 % for n?=?7) and was applied to the determination of Tl(I) in water, hair samples, and certified reference materials.

Solid-phase microfibers based on modified single-walled carbon nanotubes for extraction of chlorophenols and organochlorine pesticides

Solid-phase microextraction (SPME) based on carboxylated single-walled carbon nanotube fibers was used to extract several chlorophenols (CPs) and organochlorine pesticides (OCPs) from aqueous samples prior to their determination by GC with electron capture detection. The main parameters affecting microextraction (temperature, time, stirring rate and salting-out effect) and the conditions of the thermal desorption in the GC injector were optimized. Compared with commercial SPME fibers, the fiber presented better selectivity and sensitivity. Linear response was found for the concentration range between 2 and 1000 ng L^?1 (20–1000 ng L^?1 for CPs), and the limits of detection were in the range from 0.07 to 4.36 ng L^?1. The repeatability expressed as relative standard deviation ranged from 4.1 % to 8.2 % and the fiber-to-fiber reproducibility for four prepared fibers was between 6.5 % and 10.8 %. The method was successfully applied to the analysis of CPs and OCPs in lake water and waste water samples. Recovery was tested with spiked lake water and waste water samples, with values ranging from 89.7 % to 101.2 % in case of waste water samples.

Solid phase ligand-less extraction of cadmium(II) using a silica gel modified with an amino-functionalized ionic liquid

A method was developed for the determination of cadmium(II) by ligand-less solid phase extraction that is based on the direct retention of Cd(II) in a mini-column filled with a silica gel modified with an amino-functionalized ionic liquid. The effects of pH, sample volume and its flow rate, eluent concentration and its volume, the flow rate of eluent, and of potential interferences on extraction and desorption were optimized. Following its determination by electrothermal atomic absorption spectrometry, the detection limit for Cd(II) is 8.9 ng L^?1, and the relative standard deviation is 2.3 % (at 1.0 ng mL^?1; for n?=?5). The method was applied to the analysis of Cd(II) in a certified reference material (laver; GBW10023), and the recoveries ranged from 97.0 to104.0 %

A nanostructured ion-imprinted polymer for the selective extraction and preconcentration of ultra-trace quantities of nickel ions

We describe a nanostructured ion-imprinted polymer (IIP) for the selective preconcentration of Ni(II) ions. It was obtained by bulk polymerization from 2-vinylpyridine (the functional monomer), ethylene glycol dimethacrylate (the cross-linker), 2,2′-azobisisobutyronitrile (the initiator), alizarin red S (the nickel-binding ligand), and nickel (the template ion) in acetonitrile solution. The IIP particles were characterized by elemental analysis, X-ray diffraction, Fourier transform IR spectroscopy, thermogravimetric and differential thermal analysis, and by scanning electron microscopy. Imprinted Ni(II) ions were removed from the polymeric structure using 5 % HCl as the eluting solvent. The material is capable of selectively binding Ni(II) from solutions at pH values between (pH 8.0 being best). Both the sorption and desorption process occur within 5 min. The maximum sorbent capacity of the ion imprinted polymer is 73 mg g^?1. Following desorption, Ni(II) was determined by FAAS, with relative standard deviation and limit of detection of 3.4 % and 0.15 ng mL^?1, respectively. The method was applied to the determination of nickel in certified reference materials (soil and polymetallic gold ore), fish, vegetables, river sediments, and river water.

Speciation of inorganic arsenic in environmental waters using magnetic solid phase extraction and preconcentration followed by ICP-MS

A new method was developed for the speciation of inorganic arsenic in environmental water by using selective magnetic solid-phase extraction followed by inductively coupled plasma mass spectrometry. It is found that As(V) selectively adsorbed on amino-modified silica-coated magnetic nanoparticles (MNPs) in the pH range from 3 to 8, while As(III) is not be retained. The As(V)-loaded MNPs can be separated easily from the aqueous sample solution by simply applying an external magnetic field. The adsorbed As(V) was quantitatively recovered from the MNPs using using 1 M nitric acid. Total inorganic As was extracted after the permanganate oxidation of As(III) to As(V). Parameters affecting the separation were investigated systematically, and the optimal separation conditions were established. Under the optimal conditions, the limit of detection is 0.21 ng L^?1, and the precision is 6.8% (at 10 ng L^?1, for n?=?7). The method was applied to the speciation of inorganic arsenic in environmental water of tobacco growing area.

A novel test using dried blood spots for the chromatographic assay of methadone

A novel test has been developed for the analysis of methadone in dried blood spot specimens from patients undergoing methadone maintenance treatment. An isocratic reversed-phase high-performance liquid chromatography method with coulometric detection has been optimized for the determination of methadone. The clean-up of dried blood spots was performed by means of an original microextraction by packed sorbent procedure after microwave-assisted extraction of the drug with a suitable solvent. Extraction yields were satisfactory, always being higher than 90.0 %. The calibration curve was linear over the 4–500 ng mL^-1 concentration range. The method had satisfactory sensitivity (limit of quantitation of 4 ng mL^-1), precision (relative standard deviation less than 5.8 %), selectivity and accuracy (recovery greater than 87.0 %). It was successfully applied to dried blood spot samples collected from heroin-addicted patients undergoing methadone maintenance therapy at dosages between 40 and 240 mg day^-1. The statistical analysis (Bland–Altman plot) showed that the results were in good agreement with those found from the analysis of plasma samples obtained from the same patients. Thus, the method has proved to be suitable for the monitoring of methadone by means of dried blood spots.

Biosensor for bisphenol A leaching from baby bottles using a glassy carbon electrode modified with DNA and single walled carbon nanotubes

We have developed a biosensor for highly sensitive and selective determination of the endocrinic disruptor bisphenol A (BPA). It is based on glassy carbon electrode modified with calf thymus DNA and a composited prepared from single walled carbon nanotubes (SWNT) and Nafion. The interaction between BPA and DNA was studied by voltammetry. The binding constant was determined to be 3.55?×?10³ M^?1, and the binding site has a length of 4.3 base pairs. These electrochemical studies provide further information for a better understanding of the toxicity and carcinogenicity of BPA. Under optimal conditions, the biosensor displays a linear electrochemical response to BPA in the 10 nM to 20 μM concentration range, with a detection limit as low as 5.0 nM (at an S/N of 3). The method was successfully applied to the quantification of BPA in leachates from plastic baby bottles. Recoveries range from 94.0 % to 106.0 % which underpins the excellent performance of this SWNT-based DNA sensor.

Ultrasensitive electrochemiluminescent detection of pentachlorophenol using a multiple amplification strategy based on a hybrid material made from quantum dots,graphene, and carbon nanotubes

We report on a highly sensitive and selective electrochemiluminescence (ECL) based method for the determination of pentachlorophenol (PCP). It is based on a new hybrid material composed of CdS quantum dots (QDs), graphene, and carbon nanotubes (CNTs), and uses peroxodisulfate as the coreactant. The use of this system results in a nearly 18-fold increase in ECL intensity. On interaction between PCP and the QDs, a decrease in ECL intensity is observed at PCP in a concentration as low as 1.0 pM and over a wide linear range (from 1.0 pM to 1.0 nM). The method is hardly affected by other chlorophenols and nitrophenols, and the electrode can be recycled.

Integration of lateral flow and microarray technologies for multiplex immunoassay: application to the determination of drugs of abuse

We report on a lateral flow microarray that combines multi-spot immunochip technology and immunochromatography. It can serve as a tool for the simultaneous detection of multiple analytes. The test zone of the nitrocellulose support comprises a microarray spotted with up to 32 antigens that can capture labeled gold-antibodies after lateral flow. The detection limits and detectable concentration ranges of the assay were characterized. The method was applied to the determination of drugs of abuse (and their metabolites) in urine, specifically of morphine, amphetamine, methamphetamine, and benzoylecgonine. The assay format is rapid (10 min), and has both a low relative standard deviation (< 9 %) and high recoveries (95–114 %). The detection limits (2–20 ng mL^–1 for drugs of abuse) are comparable to those of conventional single-analyte strip methods.

Electrochemical sensor based on a carbon nanotube-modified imprinted sol–gel for selective and sensitive determination of ß2-agonists

We describe a molecularly imprinted electrochemical sensor for selective and sensitive determination of β₂-agonists. It is making use of a combination of single-wall carbon nanotubes (SWNTs) with a molecularly imprinted sol–gel. The SWNTs were introduced in order to enhance electron transport and sensitivity. The imprinted sol–gel film with its specific binding sites acts as a selective recognition element and as a preconcentrator for β₂-agonists. The morphology of the imprinted film was characterized by scanning electron microscopy. The optimized sensor displays high sensitivity and excellent selectivity for the β₂-agonists as shown for their determination in human serum samples.

Selective solid-phase extraction and separation of trace gold, palladium and platinum using activated carbon modified with ethyl-3-(2-aminoethylamino)-2-chlorobut-2-enoate

Activated carbon was chemically modified with ethyl-3-(2-aminoethylamino)-2-chlorobut-2-enoate to obtain a material for selective solid-phase extraction of trace Au(III), Pd(II) and Pt(IV) prior to their determination by inductively coupled plasma atomic emission spectrometry. Experimental conditions such as effects of pH, shaking time, sample flow rate and volume, elution and interfering ions were studied. The ions Au(III), Pd(II) and Pt(IV) can be quantitatively adsorbed on the new sorbent from solution of pH 1. The adsorbed ions were then eluted with 0.1 mol L^?1 hydrochloric acid and containing 4% thiourea. Many common ions do not interfere. The adsorption capacity of the material is 305, 92, and 126 mg g^?1 for Au(III), Pd(II) and Pt(IV), respectively, and the detection limits are 5, 11 and 9 ng mL^?1. The relative standard deviation is less than 3.0% (n?=?8) under optimum conditions. The method was validated by analyzing two certified reference materials and successfully applied to the preconcentration and determination of these ions in actual samples with satisfactory results.

Cetyltrimethylammonium-coated magnetic nanoparticles for the extraction of bromate,followed by its spectrophotometric determination

We report on a combination of magnetic solid-phase extraction and spectrophotometric determination of bromate. Cetyltrimethylammonium ion was adsorbed on the surface of phenyl-functionalized silica-coated Fe₃O₄ nanoparticles (Ph-SiO₂@Fe₃O₄), and these materials served as the sorbent. The effects of surfactant and amount of sorbent, the composition of the desorption solution, the extraction time and temperature were optimized. Under optimized conditions, an enrichment factor of 12 was achieved, and the relative standard deviation is 2.9 % (for n?=?5). The calibration plot covers the 1–50 ng mL^?1 range with reasonable linearity (r ²?>?0.998); and the limit of detection is 0.5 ng mL^?1. The method is not interfered by ionic compounds commonly found in environmental water samples. It was successfully applied to the determination of bromate in spiked water samples.

Selective solid-phase extraction of trace mercury(II) using a silica gel modified with diethylenetriamine and thiourea

We describe a solid phase extractor for selective separation and preconcentration of Hg(II) ion. It was prepared by immobilizing the adduct of diethylenetriamine and thiourea on silica gel. The effects of solution acidity, preconcentration time, sample flow rate and volume were optimized. The results show that Hg(II) can be selectively extracted from acidic solutions and in presence of common other metal ions. The adsorbent is stable, can be reused more than 10 times, and the maximum adsorption capacity is 23 mg g^?1. Hg(II) was quantified by inductively coupled plasma optical emission spectrometry. The method has a detection limit of 23 ng L^?1, and the relative standard deviation is <2 %. The procedure was validated by analyzing two standard materials (river sediment and hair powder), and was successfully applied to the preconcentration of Hg(II) in real samples.

A porous silicon immunoassay platform for fluorometric determination of α-synuclein in human cerebrospinal fluid

Levels of total and/or oligomeric α-synuclein may be used as a biomarker tool to aid in the diagnosis and development of new disease-modifying therapies. We report here on a porous silicon antibody microarray for the fluorimetric determination of cerebrospinal fluid levels of total α-synuclein, a protein involved the pathology of Parkinson’s disease. The surface of porous silicon has a 3-dimensional macro- and nanoporous structure, and this offers a large binding capacity for capturing probe molecules. Porous silicon also warrants efficient immobilization of antibodies by surface adsorption, and does not require chemical immobilization. The platform requires 10 μL of cerebrospinal fluid, and each test requires 4 h for assay only (including immobilization of capturing antibody). The limit of detection is 35 pg mL^?1 of α-synuclein in cerebrospinal fluid, and the dynamic analytical range extends from 0.01 to 100 ng·mL^?1.

Detection and quantification of proteins and cells by use of elemental mass spectrometry: progress and challenges

Much progress has been made in identification of the proteins in proteomes, and quantification of these proteins has attracted much interest. In addition to popular tandem mass spectrometric methods based on soft ionization, inductively coupled plasma mass spectrometry (ICPMS), a typical example of mass spectrometry based on hard ionization, usually used for analysis of elements, has unique advantages in absolute quantification of proteins by determination of an element with a definite stoichiometry in a protein or attached to the protein. In this Trends article, we briefly describe state-of-the-art ICPMS-based methods for quantification of proteins, emphasizing protein-labeling and element-tagging strategies developed on the basis of chemically selective reactions and/or biospecific interactions. Recent progress from protein to cell quantification by use of ICPMS is also discussed, and the possibilities and challenges of ICPMS-based protein quantification for universal, selective, or targeted quantification of proteins and cells in a biological sample are also discussed critically. We believe ICPMS-based protein quantification will become ever more important in targeted quantitative proteomics and bioanalysis in the near future.