Showing papers in "Mikrochimica Acta in 2009"

Controlled Wrinkling as a Novel Method for the Fabrication of Patterned Surfaces

Abstract: This article reviews recent applications of controlled wrinkling for creating structured and/or patterned interfaces, and its use in metrology. We discuss how wrinkles develop as a result of in-plane compression of thin sheets. As the wavelength of wrinkles is only dependent on elastic properties and thickness of the sheets, the phenomenon can be used in metrology for determination of elastic properties. The second aspect is its use for patterning and topographical structuring of surfaces. If mechanical properties and thickness are well controlled, wrinkle orientation and geometry can be tailored. Wavelengths between fractions of a micron and many micrometers are feasible. This process is based on a macroscopic deformation and upscaling to larger areas is possible which provides an attractive alternative to bottom-up or top-down approaches for surface patterning. We describe the formation of stable surface wrinkles in thin sheets of different materials having different surface chemistries, report on applications, and discuss the usefulness of wrinkles for building hierarchical structures.

Electrochemical sensors based on metal and semiconductor nanoparticles

Abstract: Metal and semiconductor nanoparticles exhibit unique optical, electrical, thermal and catalytic properties. Therefore, they have attracted considerable interest and have been employed for construction of various electrochemical sensors. This minireview gives a general view of recent advances in electrochemical sensor development based on metal and semiconductor nanoparticles covering genosensors, protein and enzyme-based sensors, gas sensors and sensor for other organic and inorganic substances. Different assay strategies based on metal and semiconductor nanoparticles for biosensor and bioelectronic applications are presented, including electrochemical, electrical, and magnetic signal transduction techniques. Electrochemical transduction principles provide signal changes in conductance, charge, potential and current. We have paid much attention to the potential-based and current-based sensors herein. Lastly, a brief introduction is given into advances concerning the role of nanoparticles, quantum dots and nanowires for nanomedicine, such as drug delivery and discovery.

Analytical nanotechnology for food analysis

Abstract: Nanotechnology involves the study and use of materials at nanoscale dimensions (nanomaterial sizes of ≤100 nm), exploiting the different physiochemical properties exhibited by these nanomaterials from the same materials at a larger scale. Nanotechnology is being demonstrated to have a large impact on many aspects of food and agricultural systems, from the development of new food packing materials to nano-delivery systems, including the analytical control of the whole food chain. In fact, the need to generate fast, reliable and precise information on the quality and security of foodstuffs and food industry has resulted in an intensive search for more selective and sensitive analytical methods. Nanotechnology is one way to achieve these goals. Although analytical nanotechnology applied to food industry is still an emerging field, chemical sensor and biosensor technology for use in this area has rather early taken advantage of the unique merits of nanotechnology and nanomaterials. This article reviews the recent progress made in analytical nanotechnology as applied to the food industry and to food analysis, with particular emphasis on nano-sensing. A brief description of the various nano-based sensing approaches is given and their capabilities and limitations are discussed. Typical examples are presented for exogenous compounds (e.g. pesticides, toxic anions, ripening gases or vitamin supplements) and endogenous compounds (from microorganisms to vitamins) in food. In addition, selected nanotechnology-based analytical methods other than sensing are described.

Determination of hydrogen peroxide with the aid of peroxidase-like Fe3O4 magnetic nanoparticles as the catalyst

Abstract: As a mimetic peroxidase, Fe3O4 magnetic nanoparticles (MNPs) were prepared and used for the determination of hydrogen peroxide (H2O2) based on their catalytic effect on the oxidation of N,N-diethyl-p-phenylenediamine sulfate (DPD). Fe3O4 MNPs were found to be able to activate H2O2 and oxidize DPD to a colored product with a strong absorption maximum at 550 nm. Under optimized conditions, the absorbance of the product responded linearly to H2O2 concentration in the range from 0.5 to 150 × 10−6 mol L−1 H2O2 with a detection limit as low as 2.5 × 10−7 mol L−1. The method was successfully applied to the determination of H2O2 in rainwater, honey and milk samples.

Simple and sensitive detection method for chromium(VI) in water using glutathione—capped CdTe quantum dots as fluorescent probes

Abstract: Water-soluble and stable CdTe quantum dots (QDs) were synthesized in aqueous solution with glutathione (GSH) as the stabilizer. GSH is employed by nature to detoxify heavy metal ions. As a result of specific interaction, the fluorescence intensity of GSH-capped QDs is selectively reduced in the presence of Cr(VI). Under the optimum conditions, the relative fluorescence intensity decreases linearly with the Cr(VI) concentration in the range from 0.01 to 1.00 µg mL−1, and the detection limit is 0.008 µg mL−1. The luminescence response of the QDs to ions markedly depended on the particle size, and a new strategy for tuning the selectivity of luminescent QDs to certain ions without changing the capping layer of the QDs can be achieved by changing the crystallite size of the QDs.

Uricase based methods for determination of uric acid in serum

Abstract: The most common methods for determination of uric acid in serum are based on the use of the enzyme uricase. Uric acid is enzymatically oxidized by oxygen to produce hydrogen peroxide, allantoin, and carbon dioxide. The four most often applied uricase methods are critically compared in this review.

Electrochemical sensor for formaldehyde based on Pt–Pd nanoparticles and a Nafion-modified glassy carbon electrode

Abstract: A novel electrochemical sensor for the determination of formaldehyde is introduced based on electrodepositing nanostructured platinum–palladium alloy in Nafion film-coated glassy carbon electrode. Bimetallic Pt–Pd nanoparticles are found to be uniformly dispersed in Nafion film, as confirmed by scanning electron microscopic analysis. Energy dispersed X-ray analysis is used to characterize the composition of metal present in the nanoparticle-modified electrodes. The electrocatalytical behavior of the electrode is investigated by cyclic voltammetry and linear sweep voltammetry. Experimental results show that the electrode displays a remarked electrocatalytic activity for the oxidation of formaldehyde and exhibits a linear relationship in the range of 10 μM to 1 mM, with a detection limit of 3 μM in acidic solution. The low detection limit, wide linear range, and high sensitivity of the sensor make it valuable for further application.

Speciation of chromium in water samples using dispersive liquid–liquid microextraction and flame atomic absorption spectrometry

Abstract: A novel method for preconcentration is described for chromium speciation at microgram per liter to sub-microgram per liter levels. It is based on selective complex formation of both Cr(VI) and Cr(III) followed by dispersive liquid–liquid microextraction and determination by microsample introduction-flame atomic absorption spectrometry. Effects influencing complex formation and extraction (such as pH, temperature, time, solvent, salinity and the amount of chelating agent) have been optimized. Enrichment factors up to 275 and 262 were obtained for Cr(VI) and total Cr, respectively. The calibration graph is linear from 0.3 to 20 µg L−1, and detection limits are 0.07 and 0.08 µg L−1 for Cr(VI) and total Cr, respectively. Relative standard deviations (RSDs) were obtained to be 2.0% for Cr(VI) and 2.6% for total Cr (n = 7).

Simultaneous determination of dopamine and serotonin using a carbon nanotubes-ionic liquid gel modified glassy carbon electrode

Abstract: An electrochemical sensor based on carbon nanotubes (CNTs)-ionic liquid (IL) composite has been developed for the simultaneous determination of serotonin (5-HT) and dopamine (DA). The CNTs-IL composite modified electrode presents excellent selectivity and sensitivity towards 5-HT and DA and eliminates the interference of ascorbic acid. The parameters which influence the determination of 5-HT and DA have been investigated. Under optimized conditions, linear calibration graphs were obtained in the range from 20 nM to 7 µM, with a detection of limit of 8 nM, for 5-HT, and in the range from 0.1 to 12 µM, with a detection of limit of 60 nM, for DA. The electrode has been applied to the assay of 5-HT and DA in human blood serum with good results.

Simultaneous determination of dopamine, uric acid and ascorbic acid with LaFeO3 nanoparticles modified electrode

Abstract: LaFeO3 nanoparticles of approximately 22 nm in size were synthesized and characterized by XRD and TEM. A novel glassy carbon electrode modified with LaFeO3 nanoparticles was constructed and characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The modified electrode exhibited strong promoting effect and high stability toward the electrochemical oxidation of dopamine (DA), which gave reversible redox peaks with a formal potential of 0.145 V (vs. Ag/AgCl) in pH 7.0 phosphate buffer solution. The anodic peak current (measured by constant potential amperometry) increased linearly with the concentration of dopamine in the range from 1.5 × 10−7 to 8.0 × 10−4 M. The detection limit was 3.0 × 10−8 M. The relative standard deviation of eight successive scans was 3.47% for 1.0 × 10−6 M DA. The interference by ascorbic acid was eliminated efficiently. The method was used to determine DA in dopamine hydrochloride injections and showed excellent sensitivity and recovery.

Selective solid-phase extraction of lead(II) from biological and natural water samples using surface-grafted lead(II)-imprinted polymers

Abstract: A new Pb(II)-imprinted amino-functionalized silica gel sorbent was synthesized by an easy one-step reaction by combining a surface imprinting technique for selective solid-phase extraction of trace Pb(II) prior to its determination by inductively coupled plasma optical emission spectrometry. The Pb(II)-imprinted amino-functionalized silica gel sorbent was characterized by Fourier transform infrared spectroscopy. Compared to non-imprinted polymer particles, the ion-imprinted polymers had higher selectivity and adsorption capacity for Pb(II). The maximum static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Pb(II) was 19.66 and 6.20 mg g−1, respectively. The largest selectivity coefficient of the Pb(II)-imprinted sorbent for Pb(II) in the presence of Cd(II) was over 450. The relative selectivity (α r) values of Pb(II)/Cd(II) were 49.3 and 46.3, which were greater than 1. The distribution ratio (D) values of Pb(II)-imprinted polymers for Pb(II) were much larger than that for Cd(II). The detection limit (3σ) was 0.20 μg L−1. The relative standard deviation was 2.0% for 11 replicate determinations. The method was validated for the analysis three certified reference materials (GBW 08301, GBW 08504, GBW 08511), and the results are in good agreement with standard values. The method was also successfully applied to the determination of trace lead in plants and water samples with satisfactory results.

Luminescent nanobeads for optical sensing and imaging of dissolved oxygen

Abstract: A variety of luminescent oxygen nanosensors were prepared by addressable staining of poly(styrene-block-vinylpyrrolidone) nanobeads with metal–ligand complexes whose luminescence is quenched by oxygen. They display optimal sensitivity in responding to dissolved oxygen in concentrations from 0 to 100% air saturation. The nanobeads based on cyclometallated iridium(III) complexes with coumarins are especially promising due to excellent brightnesses. The nanosensors respond virtually in real time to altering oxygen concentration and are capable of recording even very rapid changes in oxygen partial pressure. Signals are obtained by determination of luminescence lifetime in the frequency domain and in the time domain, and by ratiometric measurement of luminescence intensity. The nanosensors have been applied to sensing and imaging of dissolved oxygen, to monitor the consumption of oxygen during enzymatic oxidation of glucose, and to monitoring dissolved oxygen in a growing culture of E. coli.

Ionic liquid-based headspace single-drop microextraction coupled to gas chromatography for the determination of chlorobenzene derivatives

Abstract: A novel method, based on the coupling of ionic liquid-based headspace single-drop microextraction (SDME) with gas chromatography (GC), is developed for the determination of chlorobenzene derivatives. For the SDME of five chlorobenzene derivatives, a 1.0 μL 1-octyl-3-methylimidazolium hexafluorophosphate microdrop is exposed for 20 min to the headspace of a 15 ml aqueous sample containing 20% (w/v) NaCl placed in 25 ml vial at 40 °C. Then, the extractant is directly injected into the injector block of the GC instrument. To avoid ionic liquid leaking into the chromatographic column, a small glass tube is placed in the injection block. Under optimized operation conditions, linear relation between peak areas and analyte concentrations up to 1.5 mg L−1 has been obtained The detection limits range from 0.1 to 0.5 μg L−1 for the various analytes. The relative standard deviations at 1.0 μg L−1 range from 7.7 to 12.4%, and the enrichment factors from 41 to 127. The method is simple and sensitive, and does not suffer from the influence of a solvent peak. Its applicability is demonstrated by the determination of chlorobenzenes in wastewater samples.

Simultaneous determination of dopamine and serotonin by use of covalent modification of 5-hydroxytryptophan on glassy carbon electrode

Abstract: An electrochemical biosensor was fabricated by covalent modification of 5-hydroxytryptophan (5-HTP) on the surface of glassy carbon electrode (GCE). The electrode, denoted as 5-HTP/GCE, was characterized by X-ray photoelectron spectroscopy, cyclic voltammetry and differential pulse voltammetry. For comparison, tryptophan modified GCE (TRP/GCE) and serotonin modified GCE (5-HT/GCE) were prepared by the same method. It was found that electrocatalytic ability of these electrodes was in the order of 5-HTP/GCE > TRP/GCE > 5-HT/GCE for the oxidation of dopamine (DA) and 5-HT. The sensor was effective to simultaneously determine DA and 5-HT in a mixture. It can resolve the overlapping anodic peaks into two well-defined voltammetric peaks at 0.24 and 0.39 V (versus SCE). The linear response is in the range of 5.0 × 10−7–3.5 × 10−5 mol L−1 with a detection limit of 3.1 × 10−7 mol L−1 for DA, and in the range of 5.0 × 10−6–3.5 × 10−5 mol L−1 with a detection limit of 1.7 × 10−6 mol L−1 for 5-HT (s/n = 3), respectively.

A reagentless nitrite biosensor based on direct electron transfer of hemoglobin on a room temperature ionic liquid/carbon nanotube-modified electrode

Abstract: A novel amperometric biosensor for nitrite was developed by immobilization of hemoglobin (Hb) and a room temperature ionic liquid, 1-ethyl-3-methyl imidazolium tetrafluoroborate (EMIT), on a multi-walled carbon nanotubes (MWNTs) modified electrode. Compared with Hb/MWNTs modified electrode, the Hb/RTILs/MWNTs modified electrode showed better electrochemical response, indicating that EMIT can promote direct electron transfer of Hb. A pair of well-defined, quasi-reversible redox peaks of Hb with a formal potential of −0.315 V was observed. The immobilized Hb exhibited remarkable electrocatalytic activity for the reduction of nitrite. The linear response range was from 4.0 × 10−6 to 3.2 × 10−4 M with a detection limit of 8.1 × 10−7 M at a signal-to-noise ratio of 3. The resulting biosensor has been successfully applied to the determination of nitrite in water samples.

Speciation of As(III) and As(V) in water samples by dispersive liquid-liquid microextraction separation and determination by graphite furnace atomic absorption spectrometry

Abstract: A new method for the determination of inorganic arsenic species (As(III) and As(V)) was developed by dispersive liquid-liquid microextraction (DLLME) separation and graphite furnace atomic absorption spectrometry (GFAAS) detection. In the pH range of 3–5, As(III) complexes with ammonium pyrrolidinedithiocarbamate (APDC) and then can be extracted into carbon tetrachloride droplets formed by injecting the binary solution of carbon tetrachloride (extraction solvent) and methanol (dispersive solvent) into the sample solution. As(V) is not extracted at the same pH conditions and remained in the aqueous phase. After extraction and phase separation by centrifugation, the enriched As(III) in the sedimented phase was determined by GFAAS. Total inorganic arsenic was determined after reduction of As(V) to As(III) with sodium thiosulfate and potassium iodide, and As(V) was calculated by difference. Under optimized conditions, the detection limits of this method for As(III) were 36 ng L−1 with an enrichment factor of 45, and the relative standard deviation (R.S.D.%) was 3.1% (n = 11, c = 1.0 ng mL−1). The method has been applied to the speciation of As(III) and As(V) in natural water samples with satisfactory results.

Cadmium sulfide quantum dots modified by chitosan as fluorescence probe for copper (II) ion determination

Abstract: CdS quantum dots (QDs) have been prepared and modified with chitosan. Based on the quenching of fluorescence signals of the functionalized CdS QDs at 531 nm wavelength and enhancement of signals the 400–700 nm wavelength range by Cu2+ at pH 4.2, a simple, rapid and specific method for Cu2+ determination is presented. Under optimum conditions, the relative fluorescence intensity of CdS QDs is linearly proportional to copper concentration from 8.0 nmol L−1 to 3.0 μmol L−1 with a detection limit of 1.2 nmol L−1. The mechanism can be explained in terms of strong binding of Cu2+ onto the surface of CdS, resulting in a chemical displacement of Cd2+ ions and the formation of CuS on the surface of the QDs.

Buffer medium exchange in continuous cell and particle streams using ultrasonic standing wave focusing

Abstract: A microfluidic strategy to perform buffer exchange of particle and cell suspensions in a continuous flow format on, chip is presented. Ultrasonic standing wave technology is utilized to confine particulate matter to the centre of a buffer exchange channel while particle free buffer is sequentially aspirated via capillaries that branch off from the buffer exchange channel. At each such branch, clean buffer is supplied at an equal flow-rate from a capillary at the opposing channel wall, generating a sideways translation of the original buffer, laminated with a wash buffer stream. Each such junction increases the buffer exchange ratio accordingly. The reported buffer exchange system provides means to adjust buffer exchange conditions on-line by tuning the ratio of the cross-flow wash buffer relative the sample suspension flow, rate. The system performance was evaluated using 5 μm polystyrene microbeads and a dye as the model contaminant. Wash efficiencies up to 96.4% were accomplished with a 0.2% solid content bead suspension, using eight cross-flow junctions, effectively exchanging the carrier buffer twice. The corresponding data for erythrocyte washing was recorded to be 98.3% at a haematocrit of 2%.

Determination of traces of lead and cadmium using dispersive liquid-liquid microextraction followed by electrothermal atomic absorption spectrometry

Abstract: A procedure is presented for the determination of very low concentrations of lead and cadmium in water samples. Dispersive liquid-liquid microextraction with ammonium pyrrolidine dithiocarbamate is applied. The aqueous sample solution (adjusted to pH 6) is based on the rapidly mixed with of a small volume of a mixture of carbon tetrachloride and methanol. The two phases are separated by centrifugation, and the metals determined in the organic layer using electrothermal atomic absorption spectrometry. An effective chemical modification during the heating cycle is achieved by impregnating the graphite atomizer with a sodium tungstate solution. This allows well defined absorbance time profiles and low background values to be obtained during the atomization stage. The detection limits for lead and cadmium are 10 and 4 ng L−1, respectively. The procedure is applied to the determination of both analytes in bottled water, tap waters, and seawaters.

Preconcentration and determination of ultra trace amounts of palladium in water samples by dispersive liquid-liquid microextraction and graphite furnace atomic absorption spectrometry

Abstract: A highly sensitive, simple and rapid method is presented for the determination of palladium using graphite furnace atomic absorption spectrometry after its separation and preconcentration by dispersive liquid-liquid microextraction. Ultra traces of Pd were extracted and preconcentrated in acidic water samples by using 2-amino-1-cyclohexene-1-dithiocarboxylic acid as a suitable chelating agent, and carbon tetrachloride and acetone as extraction and disperser solvents, respectively. The experimental parameters were optimized in order to enhance the extraction efficiency. After optimizing the extraction conditions and various instrumental parameters, an enhancement factor of 350 was obtained. The analytical curve absorbance vs. concentration was linear over the range 0.02–0.6 µg L-1 Pd. The detection limit and relative standard deviation were 0.007 µg L-1 and 4.2%, respectively. The method was successfully applied to the determination of palladium in roadside soil and several aqueous samples.

Determination of Cu, Zn, Mn, and Pb by microcolumn packed with multiwalled carbon nanotubes on-line coupled with flame atomic absorption spectrometry

Abstract: Modified multiwalled carbon nanotubes (MWCNTs) were used as a packing material for flow injection on-line microcolumn preconcentration of trace amounts of the metal ions of Cu, Zn, Mn and Pb, and subsequent flame atomic absorption spectrometry (FAAS) in one run after desorbing the ions with hydrochloric acid and injecting them into the nebulizer of an FAAS. Parameters such as loading time, flow rate, pH, eluent concentration, and flow rate were optimized. Enrichment factors are 20.3, 14.2, 20.6 and 15.4 respectively, and the sample throughput is 25 h−1. The limits of detection (three times the standard deviation of the blank) are 0.59, 0.62, 0.28 and 1.00 µg L−1, respectively, and standard deviations range from 2.6 to 4.6% (n = 7). The method was applied to the analysis of these ions in vegetables, and accuracy assessed via recovery experiments.

Voltammetric determination of imidacloprid insecticide in selected samples using a carbon paste electrode

Abstract: The voltammetry of imidacloprid was investigated by using three kinds of carbon paste electrodes (CPEs) based on tricresyl phosphate, silicone oil, and n-tetradecane. The tricresyl phosphate-based carbon paste electrode exhibited the best analytical performance with respect to peak shape and signal intensity. The method, operated in the differential pulse voltammetric mode, was applied to the determination of imidacloprid in a river water sample and two commercial formulations and works in the concentration range from 1.7 to 30 μg mL−1, with a relative standard deviation not exceeding 2.2%. This appears to be the first application of a CPE to the voltammetric determination of neonicotinoid insecticides.

Solid-phase extraction of sulfonylurea herbicides from water samples with single-walled carbon nanotubes disk

Abstract: This study presents a new, easily made and practical solid-phase extraction disk, a single-walled carbon nanotubes (SWCNTs) disk. The properties of the disk were evaluated by extracting large volumes of aqueous solution (500–3,000 mL) spiked with trace levels of sulfonylurea herbicides, metsulfuron-methyl, chlorsulfuron, bensulfuron-methyl, pyrazosulfuron-ethyl, and chlorimuron-ethyl. The adsorption of analytes on the SWCNTs disk was more favorable at pH 3.0, and the adsorbed sulfonylurea herbicides could be eluted completely with acetonitrile (1% acetic acid) solvent. The disks were stacked to enhance their extraction ability to analytes. The triple layered SWCNTs disks system showed excellent extraction efficiency when the sample volume was up to 3,000 mL. A comparative study was conducted with a commercial C18 disk and an activated carbon disk. The SWCNTs disks showed an adsorption capacity comparable to sulfonylurea herbicides to the C18 disk and activated carbon disk, but the analytes retained on the activated carbon disk were hardly desorbed. Finally, the triple layered SWCNTs disks system was used to pretreat 1,000 mL of several environmental water samples spiked with the analytes, and satisfactory recoveries (79–102%) were obtained. Detection limits of 1.1–7.2 ng L−1 for analytes were achieved under the optimized conditions.

A novel strategy for selective detection of Ag + based on the red-shift of emission wavelength of quantum dots

Abstract: Selective determination of Ag(I) ion was accomplished based on the red-shift of the emission band of quantum dots (QDs). Under optimal conditions, a linear relationship does exist between the red-shift of the emission and the concentration of Ag(I) in the range from 1.0 × 10−7 to 1.5 × 10−5 mol L−1, with a detection limit of 5.0 × 10−8 mol L−1. The method has been successfully applied to the determination of Ag(I) ion in water samples. The possible reaction mechanism was investigated by ultraviolet–visible absorption, fluorescence, Raman spectroscopies and by high resolution transmission electron microscopy. The results suggest that the red-shift in emission be attributed to the stabilization of a charge-transfer state, but not due to the aggregation induced by AgI(I) ion.

Hemoglobin co-immobilized with silver–silver oxide nanoparticles on a bare silver electrode for hydrogen peroxide electroanalysis

Abstract: Hemoglobin (Hb) and silver–silver oxide (Ag–Ag2O) nanoparticles were co-immobilized on a bare silver electrode surface by cyclic voltammetry, and were characterized by UV–vis reflection spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy. The immobilized Hb was shown to maintain its biological activity well. Direct electron transfer between Hb and the resulting electrode was achieved without the aid of any electron mediator. The reduction currents to hydrogen peroxide (H2O2) at co-immobilized electrodes showed a linear relationship with H2O2 concentration over a concentration range from 6.0 × 10−6 to 5.0 × 10−2 mol L−1, and a detection limit of 2.0 × 10−6 mol L−1 (S/N = 3).

Fluorometric determination of water in organic solvents using europium ion-based luminescent nanospheres

Abstract: Luminescent nanospheres with strong red fluorescence were prepared from a europium(III) mixed complex with 2-thenoyltrifluoroacetone and 1,10-phenanthroline, and characterized by scanning electron microscopy and Fourier-transform infrared spectroscopy. The fluorescence of the nanospheres is quenched by traces of water, resulting in a method for determination of water in organic solvents. If excitated at 386 nm, the fluorescence intensity at 618 nm decreases linearly with the water content (vol % in ethanol) in the range 0.05 to 6.0%. The detection limit (S/N = 3) is as low as 0.002%.

Gold nanoparticles-carbon nanotubes modified sensor for electrochemical determination of organophosphate pesticides

Abstract: An electrochemical sensor was developed for the detection of organophosphate pesticides based on electrodeposition of gold nanoparticles on a multi-walled carbon nanotubes modified glassy carbon electrode. Cyclic voltammetry was employed in the process of electrodeposition. Field emission scanning electron microscope and X-ray diffraction techniques were used for characterization of the composite. Organophosphate pesticides (e.g. parathion) were determined using linear scan voltammetry. A highly linear response to parathion in the concentration range from 6.0 × 10−5 to 5.0 × 10−7 M was observed, with a detection limit of 1.0 × 10−7 M estimated at a signal-to-noise ratio of 3. The method has been applied to the analysis of parathion in real samples.

Monitoring cell cultivation in microfluidic segments by optical pH sensing with a micro flow-through fluorometer using dye-doped polymer particles

Abstract: Polymer microparticles containing an immobilized pH-sensitive dye are used for determination of pH inside microfluidic segments. The particles possess a hydrophilic surface in order to get a homogenous distribution inside the aqueous phase of microfluidic segments. The dye is coupled to the polymer matrix by a covalent bond. The pH can be determined by the read-out of fluorescence intensity. In contrast to dissolved indicator dyes, the chemical interference of the sensor particles with the surrounding solution is negligible. So, the particle-based sensing can easily be applied to the determination of pH changes during the cultivation of cells inside the microfluidic segments. The typical change of pH during cell cultivation can be used for monitoring the kinetic of cell cultivation inside single volumes in the nanoliter range, so that information about the metabolic activity of the organism can be obtained. An LED-based miniaturized flow-through fluorometer was developed to determine the fluorescence directly inside microtubes of an inner diameter of 0.5 mm. It allows measurement frequencies up to 60 Hz and is suited for characterization of fast moving large sequences of microfluidic segments.

Leaching characteristics of metals in fly ash from coal-fired power plant by sequential extraction procedure

Abstract: A modified sequential extraction procedure was developed and applied to characterize the species of metals in fly ash Two fly ash samples were collected from a coal-fired thermal power plant located in the north of China A sample was collected from the conventional pulverized coal (PC) combustor and another from the circulating fluidized bed (CFB) combustor After extraction by the proposed sequential extraction procedure, the elements in the fly ash samples were divided into a water-extractable fraction (F1), an acid-soluble fraction (F2), a reducible fraction (F3), an oxidizable fraction (F4) and a residual fraction (F5) Except for Cu, V, Cd in the PC sample and V, Zn in the CFB sample, most of the other metals were present in the residual fraction (F5), which was very difficult to release into the environment The fraction distribution patterns in the two samples were also compared The results indicated that the distribution of metals in different fractions in fly ash samples were probably impacted by different combustion processes

Electrocatalytic oxidation of bilirubin at ferrocenecarboxamide modified MWCNT–gold nanocomposite electrodes

Abstract: A glassy carbon electrode (GCE) modified with ferrocenecarboxamide, gold nanoparticles and multiwall carbon nanotubes was constructed and characterized by field emission scanning electron microscopy and cyclic voltammetry. The electrochemical behavior of bilirubin (BR) on the modified electrode was investigated and it was found that the modified electrode had an obvious electrocatalytic effect on bilirubin. Compared with a bare GCE, the modified electrode exhibited a marked enhancement in the current response for bilirubin. Amperometry was employed to investigate the electrocatalytical oxidation of bilirubin on the modified electrode. As a result, it exhibits an excellent electrocatalytic response to bilirubin with a response time of less than 5 s, a broad linear range of 1 to 100 μmol L−1, as well as good long-term stability and reproducibility.