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  • 1.
    Björefors, Fredrik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics.
    Petoral Jr, Rodrigo M.
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Uvdal, Kajsa
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Electrochemical impedance spectroscopy for investigations on ion permeation in ?-functionalized self-assembled monolayers2007In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 79, no 21, p. 8391-8398Article in journal (Refereed)
    Abstract [en]

    Electrochemical impedance spectroscopy was employed to explore the possibility of relating the permeation of electrolyte ions in ?-functionalized self-assembled monolayers to structural or polarity changes induced by interaction with metal ions. The monolayers were based on alkanethiols modified with a phosphorylated tyrosine analogue, which from previous work are known to drastically change their organization on gold surfaces upon interaction with aluminum and magnesium ions. The ion permeation was evaluated by using relatively low excitation frequencies, 1000 to 2 Hz, and quantified by an extra resistive component in the equivalent circuit (R SAM). The extent of ion permeation influenced by the dc potential, the electrolyte concentration, the functional group, and the thiol length were also investigated. It was, for example, found that RSAM decreased ~20% when the thiol organization collapsed and that RSAM increased ~4-5 times when the electrolyte concentration was decreased by 1 order of magnitude. Interesting observations were also made regarding the potential dependence of RSAM and the double layer capacitance. The evaluation of the ion permeation can be used to indirectly detect whether the organization of a SAM is influenced by, for example, electric fields or chemical and biological interactions. This analysis can be performed without addition of redox species, but is on the other hand complicated by the fact that other factors also influence the presence of ions within the monolayer. In addition, a second parallel RC process was obtained in some of the impedance spectra when using even lower frequencies, and its resistive component revealed different results compared to RSAM. Such data may be useful for the understanding of complex double layer phenomena at modified electrodes. © 2007 American Chemical Society.

  • 2.
    Bossi, A
    et al.
    Cranfield Institute Technology, Institute Biosci and Technology, Cranfield MK43 0AL, Beds, England; University Verona, Dipartimento Science and Tecnol, I-37134 Verona, Italy; .
    Piletsky, SA
    Cranfield Institute Technology, Institute Biosci and Technology, Cranfield MK43 0AL, Beds, England; University Verona, Dipartimento Science and Tecnol, I-37134 Verona, Italy; .
    Piletska, EV
    Cranfield Institute Technology, Institute Biosci and Technology, Cranfield MK43 0AL, Beds, England; University Verona, Dipartimento Science and Tecnol, I-37134 Verona, Italy; .
    Righetti, PG
    Cranfield Institute Technology, Institute Biosci and Technology, Cranfield MK43 0AL, Beds, England; University Verona, Dipartimento Science and Tecnol, I-37134 Verona, Italy; .
    Turner, APF
    Cranfield University, UK.
    An assay for ascorbic acid based on polyaniline-coated microplates2000In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 72, no 18, p. 4296-4300Article in journal (Refereed)
    Abstract [en]

    A technique for modification of the microtiter reader plates well with a polyaniline (PANI) film sensitive for ascorbic acid is presented. The principle of the analyte detection is based on monitoring the changes in optical absorption of the PANI film resulting from the reduction process initiated by ascorbic acid. The detection limit for ascorbic acid is 1 mg/L. Testing with real samples (soft drinks, fruit juices) gave good correlation of the method with iodimetric titration. High sensitivity, stability, and good reproducibility of the measurements make the proposed system an attractive alternative to traditional assays, used in medicine, ecology and biotechnology.

  • 3.
    Bossi, A
    et al.
    University Verona, Dipartimento Science and Tecnol, I-37134 Verona, Italy; Cranfield University, Institute BioScience and Technology, Cranfield MK43 0AL, Beds, England; .
    Piletsky, SA
    University Verona, Dipartimento Science and Tecnol, I-37134 Verona, Italy; Cranfield University, Institute BioScience and Technology, Cranfield MK43 0AL, Beds, England; .
    Piletska, EV
    University Verona, Dipartimento Science and Tecnol, I-37134 Verona, Italy; Cranfield University, Institute BioScience and Technology, Cranfield MK43 0AL, Beds, England; .
    Righetti, PG
    University Verona, Dipartimento Science and Tecnol, I-37134 Verona, Italy; Cranfield University, Institute BioScience and Technology, Cranfield MK43 0AL, Beds, England; .
    Turner, APF
    Cranfield University, UK.
    Surface-grafted molecularly imprinted polymers for protein recognition2001In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 73, no 21, p. 5281-5286Article in journal (Refereed)
    Abstract [en]

    A technique for coating microplate wells with molecularly imprinted polymers (MIPs) specific for proteins is presented. 3-Aminophenylboronic acid was polymerized in the presence of the following templates: microperoxidase, horseradish peroxidase, lactoperoxidase, and hemoglobin, via oxidation of the monomer by ammonium persulfate. This process resulted in the grafting of a thin polymer layer to the polystyrene surface of the microplates. Imprinting resulted in an increased affinity of the polymer toward the corresponding templates. The influence of the washing procedure, template concentration, and buffer pH on the polymer affinity was analyzed. It was shown that the stabilizing function of the support and spatial orientation of the polymer chains and template functional groups are the major factors affecting the imprint formation and template recognition. Easy preparation of the MIPs, their high stability, and their ability to recognize small and large proteins, as well as to discriminate molecules with small variations in charge, make this approach attractive and broadly applicable in biotechnology, assays and sensors.

  • 4.
    CASS, AEG
    et al.
    UNIV OXFORD,INORGAN CHEM LAB,OXFORD OX1 3QR,ENGLAND; CRANFIELD INST TECHNOL,CTR BIOTECHNOL,CRANFIELD MK43 0AL,BEDS,ENGLAND; .
    DAVIS, G
    UNIV OXFORD,INORGAN CHEM LAB,OXFORD OX1 3QR,ENGLAND; CRANFIELD INST TECHNOL,CTR BIOTECHNOL,CRANFIELD MK43 0AL,BEDS,ENGLAND; .
    FRANCIS, GD
    UNIV OXFORD,INORGAN CHEM LAB,OXFORD OX1 3QR,ENGLAND; CRANFIELD INST TECHNOL,CTR BIOTECHNOL,CRANFIELD MK43 0AL,BEDS,ENGLAND; .
    HILL, HAO
    UNIV OXFORD,INORGAN CHEM LAB,OXFORD OX1 3QR,ENGLAND; CRANFIELD INST TECHNOL,CTR BIOTECHNOL,CRANFIELD MK43 0AL,BEDS,ENGLAND; .
    ASTON, WJ
    UNIV OXFORD,INORGAN CHEM LAB,OXFORD OX1 3QR,ENGLAND; CRANFIELD INST TECHNOL,CTR BIOTECHNOL,CRANFIELD MK43 0AL,BEDS,ENGLAND; .
    HIGGINS, IJ
    UNIV OXFORD,INORGAN CHEM LAB,OXFORD OX1 3QR,ENGLAND; CRANFIELD INST TECHNOL,CTR BIOTECHNOL,CRANFIELD MK43 0AL,BEDS,ENGLAND; .
    PLOTKIN, EV
    UNIV OXFORD,INORGAN CHEM LAB,OXFORD OX1 3QR,ENGLAND; CRANFIELD INST TECHNOL,CTR BIOTECHNOL,CRANFIELD MK43 0AL,BEDS,ENGLAND; .
    SCOTT, LDL
    UNIV OXFORD,INORGAN CHEM LAB,OXFORD OX1 3QR,ENGLAND; CRANFIELD INST TECHNOL,CTR BIOTECHNOL,CRANFIELD MK43 0AL,BEDS,ENGLAND; .
    TURNER, APF
    Cranfield University, UK.
    FERROCENE-MEDIATED ENZYME ELECTRODE FOR AMPEROMETRIC DETERMINATION OF GLUCOSE1984In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 56, no 4, p. 667-671Article in journal (Refereed)
    Abstract [en]

    n/a

  • 5.
    Chan, Yang-Hsiang
    et al.
    Department of Chemistry, University of Washington, Seattle, USA.
    Gallina, Maria Elena
    Department of Chemistry, University of Washington, Seattle, USA.
    Zhang, Xuanjun
    Department of Chemistry, University of Washington, Seattle, USA.
    Wu, I-Che
    Department of Chemistry, University of Washington, Seattle, USA.
    Jin, Yuhui
    Department of Chemistry, University of Washington, Seattle, USA.
    Sun, Wei
    Department of Chemistry, University of Washington, Seattle, USA.
    Chiu, Daniel T.
    Department of Chemistry, University of Washington, Seattle, USA.
    Reversible Photoswitching of Spiropyran-Conjugated Semiconducting Polymer Dots2012In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 84, no 21, p. 9431-9438Article in journal (Refereed)
    Abstract [en]

    Semiconducting polymer dots (Pdots) recently have emerged as a new class of ultrabright fluorescent probes with promising applications in biological detection and imaging. We developed photoswitchable Pdots by conjugating photochromic spiropyran molecules onto poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,1′-3}-thiadiazole)] (PFBT). The modulation of fluorescence was achieved by ultraviolet irradiation, which converted spiropyran into its visible-absorbing merocyanine form. The merocyanine efficiently quenched the fluorescence of PFBT via Förster resonance energy transfer (FRET). We then reversed the quenching by subsequent irradiation with visible light to get back the fluorescence of PFBT. This FRET-based photomodulation of Pdot fluorescence could be repeated multiple times. We next conjugated biomolecules onto the surface of these photoswitchable Pdots and demonstrated their specific cellular and subcellular labeling to different types of cells without any noticeable nonspecific binding. We anticipate these photoswitchable and biocompatible Pdots will be useful in developing bioimaging techniques in the future.

  • 6.
    Chen, Hu
    et al.
    Nanyang Technology University, Singapore; Nanyang Technology University, Singapore; University of Loughborough, England.
    Chen, Peng
    Nanyang Technology University, Singapore; Centre Biomimet Sensor Science, Singapore.
    Huang, Jingfeng
    Nanyang Technology University, Singapore; Nanyang Technology University, Singapore.
    Selegård, Robert
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.
    Platt, Mark
    University of Loughborough, England.
    Palaniappan, Alagappan
    Nanyang Technology University, Singapore; Centre Biomimet Sensor Science, Singapore.
    Aili, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.
    Iing Yoong Tok, Alfred
    Nanyang Technology University, Singapore; Nanyang Technology University, Singapore.
    Liedberg, Bo
    Nanyang Technology University, Singapore; Centre Biomimet Sensor Science, Singapore.
    Detection of Matrilysin Activity Using Polypeptide Functionalized Reduced Graphene Oxide Field-Effect Transistor Sensor2016In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 88, no 6, p. 2994-2998Article in journal (Refereed)
    Abstract [en]

    A novel approach for rapid and sensitive detection of matrilysin (MMP-7, a biomarker involved in the degradation of various macromolecules) based on a polypeptide (JR2EC) functionalized reduced graphene oxide (rGO) field effect transistor (FET) is reported. MMP-7 specifically digests negatively charged JR2EC immobilized on rGO, thereby modulating the conductance of rGO-FET. The proposed assay enabled detection of MMP-7 at clinically relevant concentrations with a limit of detection (LOD) of 10 ng/mL (400 pM), attributed to the significant reduction of the net charge of JR2EC upon digestion by MMP-7. Quantitative detection of MMP-7 in human plasma was further demonstrated with a LOD of 40 ng/mL, illustrating the potential for the proposed methodology for tumor detection and carcinoma diagnostic (e.g., lung cancer and salivary gland cancer). Additionally, excellent specificity of the proposed assay was demonstrated using matrix metallopeptidase 1 (MMP-1), a protease of the same family. With appropriate selection and modification of polypeptides, the proposed assay could be extended for detection of other enzymes with polypeptide digestion capability.

  • 7.
    Chen, Peng
    et al.
    Nanyang Technol Univ, Singapore.
    Liu, Xiaohu
    Nanyang Technol Univ, Singapore; Tsinghua Univ, Peoples R China.
    Goyal, Garima
    Nanyang Technol Univ, Singapore.
    Tran, Nhung Thi
    Nanyang Technol Univ, Singapore; Ho Chi Minh City Univ Technol and Educ, Vietnam.
    Ho, James Chin Shing
    Nanyang Technol Univ, Singapore.
    Wang, Yi
    Nanyang Technol Univ, Singapore; Wenzhou Med Univ, Peoples R China.
    Aili, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.
    Liedbereg, Bo
    Nanyang Technol Univ, Singapore; Nanyang Technol Univ, Singapore.
    Nanoplasmonic Sensing from the Human Vision Perspective2018In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 90, no 7, p. 4916-4924Article in journal (Refereed)
    Abstract [en]

    Localized surface plasmon resonance (LSPR) constitutes a versatile technique for biodetection, exploiting the sensitivity of plasmonic nanostructures to small changes in refractive index. The optical shift in the LSPR band caused by molecular interactions in the vicinity of the nanostructures are typically amp;lt;5 nm and can readily be detected by a spectrophotometer. Widespread use of LSPR-based sensors require cost-effective devices and would benefit from sensing schemes that enables use of very simple spectrophotometers or even naked-eye detection. This paper describes a new strategy facilitating visualization of minute optical responses in nanoplasmonic bioassays by taking into account the physiology of human color vision. We demonstrate, using a set of nine different plasmonic nanoparticles, that the cyan to green transition zone at similar to 500 nm is optimal for naked-eye detection of color changes. In this wavelength range, it is possible to detect a color change corresponding to a wavelength shift of similar to 2-3 nm induced by refractive index changes in the medium or by molecular binding to the surface of the nanoparticles. This strategy also can be utilized to improve the performance of aggregation-based nanoplasmonic colorimetric assays, which enables semiquantitative naked-eye detection of matrix metalloproteinase 7 (MMP7) activity at concentrations that are at least 5 times lower than previously reported assays using spherical gold nanoparticles. We foresee significant potential of this strategy in medical diagnostic and environmental monitoring, especially in situations where basic laboratory infrastructure is sparse or even nonexistent. Finally, we demonstrate that the developed concept can be used in combination with cell phone technology and red-green-blue (RGB) analysis for sensitive and quantitative detection of MMP7.

  • 8.
    Chianella, I
    et al.
    Cranfield University, Institute Biosci and Technology, Bedford MK45 4DT, England; .
    Lotierzo, M
    Cranfield University, Institute Biosci and Technology, Bedford MK45 4DT, England; .
    Piletsky, SA
    Cranfield University, Institute Biosci and Technology, Bedford MK45 4DT, England; .
    Tothill, IE
    Cranfield University, Institute Biosci and Technology, Bedford MK45 4DT, England; .
    Chen, BN
    Cranfield University, Institute Biosci and Technology, Bedford MK45 4DT, England; .
    Karim, K
    Cranfield University, Institute Biosci and Technology, Bedford MK45 4DT, England; .
    Turner, APF
    Cranfield University, UK.
    Rational design of a polymer specific for microcystin-LR using a computational approach2002In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 74, no 6, p. 1288-1293Article in journal (Refereed)
    Abstract [en]

    A computational approach for the design of a molecularly imprinted polymer (MIP) specific for Cyanobacterial toxin microcystin-LR is presented. By using molecular modeling software, a virtual library of functional monomers was designed and screened against the target toxin, employed as a template. The monomers giving the highest binding energy were selected and used in a simulated annealing (molecular dynamics) process to investigate their interaction with the template. The stoichiomettic ratio observed from the simulated annealing study was used in MIP preparation for microcystin-LR. The monomers were copolymerized with a cross-linker in the presence of the template. A control (blank) polymer was prepared under the same conditions but in the absence of template. A competitive assay with microcystin-horseradish peroxidase conjugate was optimized and used to evaluate the affinity and cross-reactivity of the polymer. The performance of the artificial receptor was compared to the performance of monoclonal and polyclonal antibodies raised against the toxin. The results indicate that imprinted polymer has affinity and sensitivity comparable to those of polyclonal antibodies (die detection limit for microcystin-LR using the MIP-based assay was found to be 0.1 mug L-1), while superior chemical and thermal stabilities were obtained. Moreover, cross-reactivity to other toxin analogues was very low for the imprinted polymer, in contrast to the results achieved for antibodies. It is anticipated that the polymer designed could be used in assays, sensors, and solid-phase extraction.

  • 9.
    Dahlin, Andreas B.
    et al.
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Chen, Si
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Jonsson, Magnus P.
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Gunnarsson, Linda
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Kall, Mikael
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Hook, Fredrik
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    High-Resolution Microspectroscopy of Plasmonic Nanostructures for Miniaturized Biosensing2009In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 81, no 16, p. 6572-6580Article in journal (Refereed)
    Abstract [en]

    In this article, we demonstrate how to perform microscale spectroscopy of plasmonic nanostructures in order to minimize the noise when determining the resonance peak wavelength. This is accomplished using an experimental setup containing standard optical components mounted on an ordinary light microscope. We present a detailed comparison between extinction spectroscopy in transmission mode and scattering spectroscopy under dark field illumination, which shows that extinction measurements provide higher signal-to-noise in almost all situations. Furthermore, it is shown that rational selection of nanostructure, hardware components, and data analysis algorithms enables tracking of the particle plasmon resonance wavelength from a 10 mu m x 50 mu m area with a resolution of 10(-3) nm in transmission mode. We investigate how the temporal resolution, which can be improved down to 17 Ins, affects, the noise characteristics. In addition, we show how data can be acquired from an area as small as 2 mu m x 10 mu m (similar to 240 particles) at the expense of higher noise on longer time scales. In comparison with previous work on macroscopic sensor designs, this represents a sensor miniaturization of 5 orders of magnitude, without any loss in signal-to-noise performance. As a model system, we illustrate biomolecular detection using gold nanodisks prepared by colloidal lithography. The microextinction measurements of nanodisks described here provide detection of protein surface coverages as low as 40 pg/cm(2) (less than0.1% of saturated binding). In fact, the miniaturized system provides a detection limit in terms of surface coverage comparable to state of the art macroscopic sensors, while simultaneously being as close to single protein molecule detection as sensors based on a single nanoparticle.

  • 10.
    DENNISON, MJ
    et al.
    CRANFIELD UNIV,CTR BIOTECHNOL,CRANFIELD MK43 0AL,BEDS,ENGLAND; .
    HALL, JM
    CRANFIELD UNIV,CTR BIOTECHNOL,CRANFIELD MK43 0AL,BEDS,ENGLAND; .
    TURNER, APF
    Cranfield University, UK.
    GAS-PHASE MICROBIOSENSOR FOR MONITORING PHENOL VAPOR AT PPB LEVELS1995In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 67, no 21, p. 3922-3927Article in journal (Refereed)
    Abstract [en]

    A microbiosensor capable of measuring very low levels of phenol vapor directly in the gas phase has been constructed. The microbiosensor is based on the enzyme polyphenol oxidase, which catalyzes the oxidation of phenols to catechols and then to quinones, Polyphenol oxidase was immobilized in a glycerol-based gel which did not dehydrate significantly over time. An interdigitated microelectrode array was used as transducer. Phenol vapor partitioned into the glycerol gel, where it was enzymatically oxidized to quinone. Signal amplification was achieved by redox recycling of the quinone/catechol couple, This redox recycling produced a biosensor capable of measuring phenol vapor concentrations of 30 ppb. The biosensor produced a constant signal after 5 days of continuous use at room temperature and has potential application in the held of health and safety monitoring, where its ease of use, selectivity, and realtime monitoring would provide personnel with accurate data.

  • 11.
    Ekeroth, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Konradsson, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Organic Chemistry. Linköping University, The Institute of Technology.
    Björefors, Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics. Linköping University, The Institute of Technology.
    Lundström, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Liedberg, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics. Linköping University, The Institute of Technology.
    Monitoring the interfacial capacitance at self-assembled phosphate monolayers on gold electrodes upon interaction with calcium and magnesium2002In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 74, no 9, p. 1979-1985Article in journal (Refereed)
    Abstract [en]

    Electrochemical impedance spectroscopy has been used to evaluate the change in interracial capacitance upon calcium and magnesium coordination to a phosphate-modified electrode. The phosphate electrode was prepared via immobilization of phosphorylated, thiol-containing, serine analogues onto gold. Upon subjection to calcium and magnesium, a substantial drop in capacitance was observed. Magnesium displayed the largest influence on the capacitance: a 27% capacitance drop was observed upon introduction of a 1 mM solution of magnesium ions. The lowered capacitance is a result of a change in the potential and charge distribution at the film/electrolyte interface as the cations coordinate to the phosphate groups. Moreover, the relationship between electrode potential and capacitance has been investigated and reveals a significant difference between monovalent and divalent cations. As complementary information, infrared reflection absorption spectra of the phosphorylated monolayer having different counterions are presented. The results reported in this paper indicate that the phosphorylated amino acid analogue monolayers could be used in investigations of the biochemically important coordination of calcium and magnesium to phosphates and phosphorylated amino acids.

  • 12. Hatzinikolaou, DG
    et al.
    Lagesson, Verner
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Occupational and Environmental Medicine . Östergötlands Läns Landsting, Centre for Medicine, Pain and Rehabilitation Centre.
    Stavridou, AJ
    Pouli, AE
    Lagesson-Andrasko, L
    Stavrides, JC
    Analysis of the gas phase of cigarette smoke by gas chromatography coupled with UV-diode array detection2006In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 78, no 13, p. 4509-4516Article in journal (Refereed)
    Abstract [en]

    A gas chromatography method, coupled with diode array photometric spectral detection in the ultraviolet region (167-330 nm), was developed for the analysis of the gas phase of cigarette smoke. The method enabled us to identify more than 20 volatiles present in the vapor phase of cigarette smoke. In that way, all major volatile organic compounds ( including aldehydes, conjugated dienes, ketones, sulfides, furans, and single-ring aromatics), as well as nitric oxide ( NO) and hydrogen sulfide (H2S), can be analyzed in a straightforward manner through a single chromatographic run of < 50-min duration. The method can easily be applied by the introduction of a small volume of the gas-phase stream into the GC injection loop directly through the smoking apparatus exhaust circuit, thus providing an excellent alternative to available methods, which usually require extraction or concentration steps prior to any chromatographic analysis. Furthermore, all problems concerning aging of the gas phase are eliminated. Twelve compounds ( including NO) were chosen for quantification through the use of appropriate calibration standards. Comparison of the vapor phase yields of these compounds for the reference cigarette Kentucky 1R4F with already reported data indicates that this method is very reliable as far as accuracy and reproducibility of the results are concerned. Finally, the proposed methodology was used to compare the concentration of these cigarette smoke gas-phase constituents among individual puffs.

  • 13.
    Jonsson, Magnus P.
    et al.
    Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
    Dahlin, Andreas B.
    Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
    Feuz, Laurent
    Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
    Petronis, Sarunas
    Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
    Hook, Fredrik
    Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden.
    Locally Functionalized Short-Range Ordered Nanoplasmonic Pores for Bioanalytical Sensing2010In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 82, no 5, p. 2087-2094Article in journal (Refereed)
    Abstract [en]

    Nanoplasmonic sensors based on short-range ordered nano-holes in thin metal films and discrete metal nanoparticles are known to provide similar sensing performance. However, a perforated metal film is unique in the sense that the holes can be designed to penetrate through the substrate, thereby also fulfilling the role of nanofluidic channels. This paper presents a bioanalytical sensing concept based on short-range ordered nanoplasmonic pores (diameter 150 nm) penetrating through a thin (around 250 nm) multilayer membrane composed of gold and silicon nitride (SiN) that is Supported on a Si wafer. Also, a fabrication scheme that enables parallel production of multiple (more than 50) separate sensor chips or more than 1000 separate nanoplasmonic membranes on it single wafer is presented. Together with the localization of the sensitivity to within such short-range ordered nanoholes, the structure provides it two-dimensional nanofluidic network, sized in the order of 100 x 100 mu m(2), with nanoplasmon active regions localized to each individual nanochannel. A material-specific surface-modification scheme was developed to promote specific binding of target molecules on the optically active gold regions only, while suppressing nonspecific adsorption on SiN. Using this protocol, and by monitoring the temporal variation in the plasmon resonance of the structure, we demonstrate flow-through nanoplasmonic sensing of specific biorecognition reactions with a signal-to-noise ratio of around 50 at a temporal resolution below 190 ms. With flow, the uptake was demonstrated to be at least 1 order of magnitude faster than under stagnant conditions, while still keeping the sample consumption at a minimum.

  • 14.
    Jonsson, Magnus P.
    et al.
    Division of Solid State Physics, Department of Physics, Lund University, Lund, Sweden..
    Jonsson, Peter
    Division of Solid State Physics, Department of Physics, Lund University, Lund, Sweden..
    Hook, Fredrik
    Division of Solid State Physics, Department of Physics, Lund University, Lund, Sweden..
    Simultaneous Nanoplasmonic and Quartz Crystal Microbalance Sensing: Analysis of Biomolecular Conformational Changes and Quantification of the Bound Molecular Mass2008In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 80, no 21, p. 7988-7995Article in journal (Refereed)
    Abstract [en]

    This paper presents a study of supported lipid bilayer (SIB) formation and subsequent protein binding using a sensor that combines localized surface plasmon resonance (LSPR) and quartz crystal microbalance with dissipation (QCM-D) monitoring. The LSPR activity arises from silicon oxide (SiOx) coated nanometric apertures in a thin gold film, which also serves as the active electrode of a QCM-D crystal. Both transducer principles provide signatures for the formation of a SLB upon adsorption and subsequent rupture of adsorbed lipid vesicles. However, the two techniques are sensitive over different regions of the sample: LSPR primarily inside and on the rim of the holes and QCM-D primarily on the planar areas between the holes. Although the dimension of the lipid vesicles is on the same order as the dimension of the nanoholes, it is concluded from the response of the combined system that vesicle rupture in the nanoholes and on the planar region between the holes is synchronized. Furthermore, by determining the thickness of the SLB from the QCM-D response, the characteristic decay length of the LSPR field intensity could be determined. This made it possible not only to determine the mass and refractive index of the homogeneous SLB but also to postulate a generic means to quantify the LSPR response in terms of mass-uptake also for nonhomogeneous films. This is exemplified by measuring the adsorbed lipid mass during vesicle adsorption, yielding the critical lipid vesicle coverage at which spontaneous rupture into a planar bilayer occurs. The generic applicability and versatility of the method is demonstrated from specific protein binding to a functionalized SLB. From the absolute refractive index of the protein, provided from the LSPR data alone, it was possible to determine both the effective thickness of the protein film and the molecular mass (or number) of bound protein.

  • 15.
    Kashefi-Kheyrabadi, Leila
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, The Institute of Technology. University of Isfahan, Iran.
    Mehrgardi, Masoud
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, The Institute of Technology. University of Isfahan, Iran.
    Wiechec, Emilia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Turner, Anthony P.F.
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, The Institute of Technology.
    Tiwari, Ashutosh
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, The Institute of Technology.
    Ultrasensitive detection of human liver hepatocellular carcinoma (HepG2) cells using a label-free aptasensor2014In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 86, no 10, p. 4956-4960Article in journal (Refereed)
    Abstract [en]

    Liver cancer is one of the most common cancers in the world and has no effective cure, especially in later stages. The development of a tangible protocol for early diagnosis of this disease remains a major challenge. In the present manuscript, an aptamer-based, label-free electrochemical biosensor for the sensitive detection of HepG2, a hepatocellular carcinoma cell line, is described. The target cells are captured in a sandwich architecture using TLS11a aptamer covalently attached to a gold surface and a secondary TLS11a aptamer. The application of TLS11a aptamer as a recognition layer resulted in a sensor with high affinity for HepG2 cancer cells in comparison with control cancer cells of human prostate, breast and colon tumours. The aptasensor delivered a wide linear dynamic range over 1 × 102 – 1 × 106 cell/mL, with a detection limit of 2 cell/mL. This protocol provides a precise method for sensitive detection of liver cancer with significant advantages in terms of simplicity, low cost, and stability.

  • 16.
    Kim, Taehoon H.
    et al.
    DGIST, South Korea.
    Hahn, Young Ki
    Samsung Elect, South Korea.
    Lee, Jungmin
    DGIST, South Korea.
    van Noort, Danny
    Linköping University, Department of Physics, Chemistry and Biology, Biotechnology. Linköping University, Faculty of Science & Engineering. DGIST, South Korea.
    Kim, Minseok S.
    DGIST, South Korea.
    Solenoid Driven Pressure Valve System: Toward Versatile Fluidic Control in Paper Microfluidics2018In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 90, no 4, p. 2534-2541Article in journal (Refereed)
    Abstract [en]

    As paper-based diagnostics has become predominantly driven by more advanced microfluidic technology, many of the research efforts are still focused on developing reliable and versatile fluidic control devices, apart from improving sensitivity and reproducibility. In this work, we introduce a novel and robust paper fluidic control system enabling versatile fluidic control. The system comprises a linear push-pull solenoid and an Arduino Uno micro controller. The precisely controlled pressure exerted on the paper stops the flow. We first determined the stroke distance of the solenoid to obtain a constant pressure while examining the fluidic time delay as a function of the pressure. Results showed that strips of grade 1 chromatography paper had superior reproducibility in fluid transport. Next, we characterized the reproducibility of the fluidic velocity which depends on the type and grade of paper used. As such, we were able to control the flow velocity on the paper and also achieve a complete stop of flow with a pressure over 2.0 MPa. Notably, after the actuation of the pressure driven valve (PDV), the previously pressed area regained its original flow properties. This means that, even on a previously pressed area, multiple valve operations can be successfully conducted. To the best of our knowledge, this is the first demonstration of an active and repetitive valve operation in paper microfluidics. As a proof of concept, we have chosen to perform a multistep detection system in the form of an enzyme-linked immunosorbent assay with mouse IgG as the target analyte.

  • 17.
    Klett, Oliver
    et al.
    Uppsala universitet.
    Björefors, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics .
    Nyholm, Leif
    Uppsala universitet.
    Elimination of High-Voltage Field Effects in End Column Electrochemical Detection in Capillary Electrophoresis by Use of On-Chip Microband Electrodes2001In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 73, no 8, p. 1909-1915Article in journal (Refereed)
  • 18.
    Kroger, S
    et al.
    Cranfield University, Cranfield Biotechnol Centre, Cranfield MK43 0AL, Beds, England; .
    Setford, SJ
    Cranfield University, Cranfield Biotechnol Centre, Cranfield MK43 0AL, Beds, England; .
    Turner, APF
    Cranfield University, UK.
    Immunosensor for 2,4-dichlorophenoxyacetic acid in aqueous organic solvent soil extracts1998In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 70, no 23, p. 5047-5053Article in journal (Refereed)
    Abstract [en]

    The development of a simple electrochemical immunoassay procedure for the field-based quantification of the herbicide 2,4-D in methanolic soil extracts is presented. The sensor utilizes a competitive immunoassay format incorporating an immobilized antigen complex at the surface of a disposable screen-printed working electrode element, The extent of glucose oxidase-labeled antibody binding td the antigen-electrode is determined amperometrically and is related to sample analyte concentration. The performance of the sensor is assessed in buffer, 30% methanol, and methanolic soil extracts. The device is capable of quantifying 2,4-D in all three matrixes at the low ppm level with coefficient of variation values of 6.2-33.6%. The causes of the variation observed in the sensor response indifferent soil matrixes are examined and improvements proposed. The sensor, tested in parallel with a commercial 2,4-D immunoassay test kit, yields comparable quantitative data and detection limits while exhibiting greater assay simplicity.

  • 19.
    Kroger, S
    et al.
    Cranfield University, Cranfield Biotechnol Centre, Cranfield MK43 0AL, Beds, England; University Lund, Centre Chemistry, Department Pure and Appl Biochem, S-22100 Lund, Sweden; .
    Turner, APF
    Cranfield University, UK.
    Mosbach, K
    Cranfield University, Cranfield Biotechnol Centre, Cranfield MK43 0AL, Beds, England; University Lund, Centre Chemistry, Department Pure and Appl Biochem, S-22100 Lund, Sweden; .
    Haupt, K
    Cranfield University, Cranfield Biotechnol Centre, Cranfield MK43 0AL, Beds, England; University Lund, Centre Chemistry, Department Pure and Appl Biochem, S-22100 Lund, Sweden; .
    Imprinted polymer based sensor system for herbicides using differential-pulse voltammetry on screen printed electrodes1999In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 71, no 17, p. 3698-3702Article in journal (Refereed)
    Abstract [en]

    A sensor system for the herbicide 2,4-dichlorophenoxyacetic acid has been developed based on specific recognition of the analyte by a molecularly imprinted polymer and electrochemical detection using disposable screen-printed electrodes. The method involves a competitive binding step with a nonrelated electrochemically active probe. For batch binding assays, imprinted polymer particles are incubated in suspension with the analyte and the probe, followed by centrifugation and quantification of the unbound probe in die supernatant. Two different compounds, namely 2,4-dichlorophenol and homogentisic acid, were tested as potential electroactive probes. Both compounds could be conveniently detected by differential-pulse voltammetry on screen-printed, solvent-resistant three-electrode systems having carbon working electrodes. Whereas 2,4-dichlorophenol showed very high nonspecific binding to the polymer, homogentisic acid bound specifically to the imprinted sites and thus allowed calibration curves for the analyte in the micromolar range to be recorded. An integrated sensor was developed by coating the imprinted polymer particles directly onto the working electrode. Following incubation of the modified electrode in a solution containing the analyte and the probe, the bound fraction of the probe is quantified. This system provides a cheap, disposable sensor for rapid determination of environmentally relevant and other analytes.

  • 20.
    Lestremau, F.
    et al.
    Lab. Genie Environnement Industriel, Ecole des Mines d'Alès, 6, Avenue de Clavières, 30319 Alès Cedex, France.
    Andersson, F.A.T.
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Desauziers, V.
    Lab. Genie Environnement Industriel, Ecole des Mines d'Alès, 6, Avenue de Clavières, 30319 Alès Cedex, France.
    Fanlo, J.-L.
    Lab. Genie Environnement Industriel, Ecole des Mines d'Alès, 6, Avenue de Clavières, 30319 Alès Cedex, France.
    Evaluation of solid-phase microextraction for time-weighted average sampling of volatile sulfur compounds at ppb concentrations2003In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 75, no 11, p. 2626-2632Article in journal (Refereed)
    Abstract [en]

    The potential of solid-phase microextraction (SPME) for time-weighted average (TWA) sampling of volatile sulfur compounds in air at ppb concentrations was investigated. The target compounds (hydrogen sulfide, methanethiol (MeSH), ethanethiol (EtSH), dimethyl sulfide (Me2S), and dimethyl disulfide (Me2S2)) were extracted using SPME with a Carboxen-poly(dimethylsiloxane) fiber coating, and diffusion was controlled by keeping the fiber retracted within the needle of the sampling device. The effects of several important experimental variables (air velocity, direction of air flow, analyte concentration, humidity, temperature, extraction time) were studied. The uptake by the fiber was not affected by the direction of the air flow or the air velocity. The effects of concentration, humidity, temperature, and extraction time were examined in experiments with a central composite face design. The results showed that all or most of the investigated parameters had a significant impact on the uptake rates of H2S, MeSH, EtSH, and Me2S, which invalidated time-weighted average sampling of these compounds by SPME under the tested conditions. Moreover, reverse diffusion of H2S, MeSH, and EtSH occurred at 40% relative humidity. For Me2S2, the uptake rate had a variation of only 8% within the whole experimental domain, and the experimental value derived for the uptake rate was consistent with the theoretical value. This result was confirmed by comparative analyses of industrial samples by the standard addition method. Therefore, SPME appears to be a suitable technique for TWA sampling of Me2S2 using the Carboxen-poly(dimethylsiloxane) fiber coating. Finally, in an investigation of potential losses during storage of the fiber, no significant losses of the target compounds were detected after 3 days at -80 °C.

  • 21.
    Liu, Xiaohu
    et al.
    Nanyang Technology University, Singapore .
    Wang, Yi
    Nanyang Technology University, Singapore .
    Chen, Peng
    Nanyang Technology University, Singapore .
    Wang, Yusong
    Nanyang Technology University, Singapore .
    Mang, Jinling
    Nanyang Technology University, Singapore .
    Aili, Daniel
    Nanyang Technology University, Singapore .
    Liedberg, Bo
    Nanyang Technology University, Singapore .
    Biofunctionalized Gold Nanoparticles for Colorimetric Sensing of Botulinum Neurotoxin A Light Chain2014In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 86, no 5, p. 2345-2352Article in journal (Refereed)
    Abstract [en]

    Botulinum neurotoxin is considered as one of the most toxic food-borne substances and is a potential bioweapon accessible to terrorists. The development of an accurate, convenient, and rapid assay for botulinum neurotoxins is therefore highly desirable for addressing biosafety concerns. Herein, novel biotinylated peptide substrates designed to mimic synaptosomal-associated protein 25 (SNAP-25) are utilized in gold nanoparticle-based assays for colorimetric detection of botulinum neurotoxin serotype A light chain (BoLcA). In these proteolytic assays, biotinylated peptides serve as triggers for the aggregation of gold nanoparticles, while the cleavage of these peptides by BoLcA prevents nanoparticle aggregation. Two different assay strategies are described, demonstrating limits of detection ranging from 5 to 0.1 nM of BoLcA with an overall assay time of 4 h. These hybrid enzyme-responsive nanomaterials provide rapid and sensitive detection for one of the most toxic substances known to man.

  • 22.
    Lopez-Alonso, Ana
    et al.
    Royal Coll Surgeons Ireland, Ireland .
    Jose, Bincy
    Dublin City University, Ireland .
    Somers, Martin
    Dublin City University, Ireland .
    Egan, Karl
    Royal Coll Surgeons Ireland, Ireland .
    Foley, David P.
    Beaumont Hospital, Ireland .
    Ricco, Antonio J.
    Dublin City University, Ireland .
    Ramstrom, Sofia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences. Royal Coll Surgeons Ireland, Ireland .
    Basabe-Desmonts, Lourdes
    Dublin City University, Ireland .
    Kenny, Dermot
    Royal Coll Surgeons Ireland, Ireland .
    Individual Platelet Adhesion Assay: Measuring Platelet Function and Antiplatelet Therapies in Whole Blood via Digital Quantification of Cell Adhesion2013In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 85, no 13, p. 6497-6504Article in journal (Refereed)
    Abstract [en]

    Widespread monitoring of platelet function and the effect of antiplatelet drugs will improve outcomes in cardiovascular patients, but platelet function testing is not routine in clinical practice. We report a rapid, accurate methodology to quantify platelet-protein interactions: a microarray of contact-printed 6-mu m fibrinogen dots on a transparent substrate binds platelets from whole blood, one platelet per dot. The fractional occupancy of an array of fibrinogen dots after a predefined incubation time quantitatively assays platelet adhesion to the protein matrix. We demonstrate this technique by measurement of platelet adhesion to fibrinogen as a means to quantify the effect of the P2Y(12) and alpha IIb beta 3 receptor inhibitors cangrelor and abciximab, respectively, both in vitro-by incubating the drug with a freshly drawn blood sample-and in blood from patients treated with antiplatelet agents. The effects of single- and dual-antiplatelet therapy are also assessed. Results from this platelet-binding assay are well correlated with standard techniques including flow cytometry and light transmission aggregometry. This assay technology, readily integrated with microfluidic platforms, is generally applicable to the assay of cell-protein interactions and promises more effective, rapid assay of drug effects in cardiovascular disease patients.

  • 23.
    Mak, Wing Cheung
    et al.
    Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
    Cheung, Kwan Yee
    Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
    Trau, Dieter
    National University of Singapore.
    Warsinke, Axel
    University of Potsdam, Golm, Germany.
    Scheller, Frieder
    University of Potsdam, Golm, Germany.
    Renneberg, Reinhard
    Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
    Electrochemical bioassay utilizing encapsulated electrochemical active microcrystal biolabels2005In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 77, no 9, p. 2835-2841Article in journal (Refereed)
    Abstract [en]

    A new approach to perform electrochemical immunoassay based on the utilization of encapsulated microcrystal was developed. The microcrystal labels create a “supernova effect” upon exposure to a desired releasing agent. The microcrystal cores dissolve, and large amounts of signal-generating molecules diffuse across the capsule wall into the outer environment. Layer-by-Layer (LbL) technology was employed for the encapsulation of electrochemical signal-generating microcrystals (ferrocene microcrystals). The encapsulated microcrystals were conjugated with antibody molecules through the adsorption process. The biofunctionalized microcrystals were utilized as a probe for immunoassays. The microcrystal-based label system provided a high-signal molecule to antibody (S/P) ratio of 104−105. Microcrystal biolabels with different antibody surface coverage (1.60−5.05 mg m-2) were subjected to a solid-phase immunoassay for the detection of mouse immunoglobulin G (M-IgG) molecules. The microcrystal-based immunoassay for the detection of M-IgG performed with microcrystals having antibody surface coverage of 5.05 mg m-2 showed a sensitivity of 3.93 nA μg-1 L-1 with a detection limit of 2.82 μg L-1.

  • 24.
    Michno, Wojciech
    et al.
    Univ Gothenburg, Sweden.
    Kaya, Ibrahim
    Univ Gothenburg, Sweden.
    Nyström, Sofie
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Guerard, Laurent
    Univ Gothenburg, Sweden; Univ Basel, Switzerland.
    Nilsson, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Hammarström, Per
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Blennow, Kaj
    Univ Gothenburg, Sweden; Sahlgrens Univ Hosp, Sweden.
    Zetterberg, Henrik
    Univ Gothenburg, Sweden; Sahlgrens Univ Hosp, Sweden; UCL, England.
    Hanrieder, Jorg
    Univ Gothenburg, Sweden; UCL, England; Chalmers Univ Technol, Sweden.
    Multimodal Chemical Imaging of Amyloid Plaque Polymorphism Reveals A beta Aggregation Dependent Anionic Lipid Accumulations and Metabolism2018In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 90, no 13, p. 8130-8138Article in journal (Refereed)
    Abstract [en]

    Amyloid plaque formation constitutes one of the main pathological hallmarks of Alzheimers disease (AD) and is suggested to be a critical factor driving disease pathogenesis. Interestingly, in patients that display amyloid pathology but remain cognitively normal, A beta deposits are predominantly of diffuse morphology suggesting that cored plaque formation is primarily associated with cognitive deterioration and AD pathogenesis. Little is known about the molecular mechanism responsible for conversion of monomeric A beta into neurotoxic aggregates and the predominantly cored deposits observed in AD. The structural diversity among A beta plaques, including cored/compact- and diffuse, may be linked to their distinct A beta profile and other chemical species including neuronal lipids. We developed a novel, chemical imaging paradigm combining matrix assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) and fluorescent amyloid staining. This multimodal imaging approach was used to probe the lipid chemistry associated with structural plaque heterogeneity in transgenic AD mice (tgAPP(Swe)) and was correlated to A beta profiles determined by subsequent laser microdissection and immunoprecipitation-mass spectrometry. Multivariate image analysis revealed an inverse localization of ceramides and their matching metabolites to diffuse and cored structures within single plaques, respectively. Moreover, phosphatidylinositols implicated in AD pathogenesis, were found to localize to the diffuse A beta structures and correlate with A beta 1-42. Further, lysophospholipids implicated in neuroinflammation were increased in all A beta deposits. The results support previous clinical findings on the importance of lipid disturbances in AD pathophysiology and associated sphingolipid processing. These data highlight the potential of multimodal imaging as a powerful technology to probe neuropathological mechanisms.

  • 25.
    Newman, Jeffrey D.
    et al.
    Cranfield university, UK.
    White, Stephen F.
    Cranfield university, UK.
    Tothill, Ibtisam E.
    Cranfield university, UK.
    Turner, Anthony P. F.
    Cranfield University, UK.
    Catalytic materials, membranes and fabrication technologies suitable for the construction of amperometric biosensors1995In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 67, no 24, p. 4594-4599Article in journal (Other academic)
    Abstract [en]

    A selection of recently available catalytic carbon powders were assessed and compared with the more conventionally used platinized material. Their suitability for incorporation in amperometric biosensors is discussed, In conjunction with this study, methods of applying membranes to the surfaces of these devices were investigated. Advanced fabrication technologies, potentially suitable for scale-up of sensor production, such as screen printing and ink-jet printing, were used for manufacture of the complete sensor structure. Hydrogen peroxide-sensing electrodes and glucose biosensors were produced as model systems, demonstrating the advantages of these approaches. The commercially available rhodinized carbon MCA4 produced a high current density at low potentials over a plateau region (300-400 mV vs SCE). In addition, direct oxidation of glucose (seen with platinized carbon) was not observed at the chosen potential of +350 mV. Further interference studies using fermentation media highlighted its suitability as an electrode material for use in complex samples. Ink-jet printing proved to be a successful method for the deposition of Nafion membranes of defined and reproducible geometry.

  • 26. Nilsson, S
    et al.
    Svedberg, M
    Pettersson, J
    Björefors, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics .
    Markides, K
    Nyholm, L
    Evaluations of the stability of sheathless electrospray ionization mass spectrometry emitters using electrochemical techniques2001In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 73, no 19, p. 4607-4616Article in journal (Refereed)
    Abstract [en]

    The processes that cause the failure of sheathless electrospray ionization (ESI) emitters, based on different kinds of gold coatings on fused-silica capillaries, are described and explained. The methods chosen for this study include electrochemical methods, ICPMS analysis of the electrolytes used, SEM studies, and electrospray experiments. Generally, the failure occurs by loss of the conductive coating. It is shown that emitters with sputter-coated gold lose their coatings because of mechanical stress caused by the gas evolution accompanying water oxidation or reduction. Emitters with gold coatings on top of adhesion layers of chromium and nickel alloy withstand this mechanical stress and have excellent durability when operating as cathodes. When operating as anodes, the adhesion layer is electrochemically dissolved through the gold film, and the gold film then flakes off. It is shown that the conductive coating behaves as a cathode even in the positive electrospray mode when the magnitude of a superimposed reductive electrophoretic current exceeds that of the oxidative electrospray current. Fairy-dust coatings developed in our laboratory (see Barnidge, D. R., et al. Anal. Chem. 1999, 71, 4115-4118) by gluing gold dust onto the emitter, are unaffected by the mechanical stress due to gas evolution. When oxidized, the fairy-dust coatings show an increased surface roughness and decreased conductivities due to the formation of gold oxide. The resistance of this oxide layer is however negligible in comparison with that of the gas phase in ESI. Furthermore, since no flaking and only negligible electrochemical etching of gold was found, practically unlimited emitter lifetimes may be achieved with fairy-dust coatings.

  • 27.
    Pasitka, Laura
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biotechnology. Linköping University, Faculty of Science & Engineering.
    van Noort, Danny
    Linköping University, Department of Physics, Chemistry and Biology, Biotechnology. Linköping University, Faculty of Science & Engineering.
    Lim, Wanyoung
    Sungkyunkwan Univ, South Korea.
    Park, Sungsu
    Sungkyunkwan Univ, South Korea.
    Mandenius, Carl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Biotechnology. Linköping University, Faculty of Science & Engineering.
    A Microbore Tubing Based Spiral for Multistep Cell Fractionation2018In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 90, no 21, p. 12909-12916Article in journal (Refereed)
    Abstract [en]

    Cells were separated with the aid of a multistep spiral fractionation device, utilizing hydrodynamic forces in a spiral tubing. The spiral was fabricated using "off-the-shelf microbore tubing, allowing for cheap and fast prototyping to achieve optimal cell separation. As a first step, a model system with 20 and 40 mu m beads was used to demonstrate the effectiveness of the multistep separation device. With an initial purity of 5%, a separation purity of 83% was achieved after a two-step separation with the addition of 0.1% polyethylene glycol (PEG)-8000. Next, doxorubicinresistant polyploid giant breast cancer cells (MDA-MB-231) were separated from doxorubicin-sensitive monoploid small breast cancer cells in the same fashion as the beads, resulting in a purity of around 40%, while maintaining a cell viability of more than 90%. Combined with basic cell analytical methods, the hydrodynamic separation principle of the device could be envisaged to be useful for a variety of cell fractionation needs in cell biology and in clinical applications.

  • 28.
    Perez, FG
    et al.
    University Florence, Dipartimento Sanita Pubbl Epidemiol and Chim Analit, Florence, Italy; .
    Mascini, M
    University Florence, Dipartimento Sanita Pubbl Epidemiol and Chim Analit, Florence, Italy; .
    Tothill, IE
    University Florence, Dipartimento Sanita Pubbl Epidemiol and Chim Analit, Florence, Italy; .
    Turner, APF
    Cranfield University, UK.
    Immunomagnetic separation with mediated flow injection analysis amperometric detection of viable Escherichia coli O1571998In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 70, no 11, p. 2380-2386Article in journal (Refereed)
    Abstract [en]

    The coupling of an immunological separation (using immunomagnetic beads) with amperometric now injection analysis detection of viable bacteria is presented. Using a solution containing Escherichia coli O157, the electrochemical response with two different mediators [potassium hexacyanoferrate(III) and 2,6-dichlorophenolindophenol] was evaluated in the FIA system. Antibody-derivatized Dynabeads were used to selectively separate E. coli O157 from a matrix The kinetics and the capacity parameters regarding the attachment of bacteria to the immunobeads were studied. The immunomagnetic separation was then used in conjunction with electrochemical detection to measure the concentration of viable bacteria. A calibration curve of colony-forming units (du) against electrochemical response was obtained. The detection limit for this rapid microbiological method was 10(5) cfu mL(-1), and the complete assay was performed in 2 h. Some advantages over ELISA methods are the direct detection of viable cells (and not total bacterial load) and the need for only one antibody (not enzyme-labeled), thus making the assay faster (only one washing step is necessary) and less expensive.

  • 29.
    Piletsky, SA
    et al.
    Cranfield University, Institute Biosci and Technology, Cranfield MK43 0AL, Beds, England; .
    Piletska, EV
    Cranfield University, Institute Biosci and Technology, Cranfield MK43 0AL, Beds, England; .
    Chen, BN
    Cranfield University, Institute Biosci and Technology, Cranfield MK43 0AL, Beds, England; .
    Karim, K
    Cranfield University, Institute Biosci and Technology, Cranfield MK43 0AL, Beds, England; .
    Weston, D
    Cranfield University, Institute Biosci and Technology, Cranfield MK43 0AL, Beds, England; .
    Barrett, G
    Cranfield University, Institute Biosci and Technology, Cranfield MK43 0AL, Beds, England; .
    Lowe, P
    Cranfield University, Institute Biosci and Technology, Cranfield MK43 0AL, Beds, England; .
    Turner, APF
    Cranfield University, UK.
    Chemical grafting of molecularly imprinted homopolymers to the surface of microplates. Application of artificial adrenergic receptor in enzyme-linked assay for beta-agonists determination2000In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 72, no 18, p. 4381-4385Article in journal (Refereed)
    Abstract [en]

    A technique for coating of microplate weds with a molecularly imprinted polymer (MTP), specific for epinephrine, is presented. 3-Aminophenylboronic acid was polymerized in the presence of epinephrine using oxidation of the monomer by ammonium persulfate. This process resulted in the grafting of a thin polymer layer onto the polystyrene surface of the microplates. The polymer affinity was determined by an enzyme-linked assay using a conjugate of horseradish peroxidase and norepinephrine (HRP-N). It was found that imprinting resulted in increased affinity of the polymer toward HRP-N and epinephrine. Influence of the buffer pH and concentration on the polymer affinity was analyzed. It was shown that the MIP-coated microplates could be used for assay development and drug screening. The high stability of the polymers and good reproducibility of the measurements make MIP coating an attractive alternative to traditional antibodies or receptors, used in ELISA.

  • 30. Qvarnström, Johanna
    et al.
    Lambertsson, Lars
    Havarinasab, Said
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Molecular and Clinical Medicine, Molecular and Immunological Pathology. Östergötlands Läns Landsting, Centre for Laboratory Medicine, Department of Clinical Pathology and Clinical Genetics.
    Hultman, Per
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Molecular and Clinical Medicine, Molecular and Immunological Pathology. Östergötlands Läns Landsting, Centre for Laboratory Medicine, Department of Clinical Pathology and Clinical Genetics.
    Frech, Wolfgang
    Determination of methylmercury, ethylmercury, and inorganic mercury in mouse tissues, following administration of thimerosal, by species-specific isotope dilution GC-inductively coupled plasma-MS2003In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 75, no 16, p. 4120-4124Article in journal (Refereed)
    Abstract [en]

    Isotopically enriched HgO standards were used to synthesize CH 3200Hg+ and C2H5199Hg+ using Grignard re-agents. These species were employed for isotope dilution GC-ICPMS to study uptake and biotransformation of ethylmercury in mice treated with thimerosal, (sodium ethylmercurithiosalicylate) 10 mg L-1 in drinking water ad libitum for 1, 2.5, 6, or 14 days. Prior to analysis, samples were spiked with aqueous solutions of CH3200Hg+, C2H 5199Hg+, and 201Hg2+ and then digested in 20% tetramethylammonium hydroxide and extracted at pH 9 with DDTC/toluene. Extracted mercury species were reacted with butylmagnesium chloride to form butylated derivatives. Absolute detection limits for CH 3Hg+, C2H5Hg+, and Hg2+ were 0.4, 0.2, and 0.6 pg on the basis of 3s of five separate blanks. Up to 9% of the C2H5Hg+ was decomposed to Hg2+ during sample preparation, and it is therefore crucial to use a species-specific internal standard when determining ethylmercury. No demethylation, methylation, or ethylation during sample preparation was detected. The ethylmercury component of thimerosal was rapidly taken up in the organs of the mice (kidney, liver, and mesenterial lymph nodes), and concentrations of C2H5Hg+ as well as Hg2+ increased over the 14 days of thimerosal treatment. This shows that C2H5Hg+ in mice to a large degree is degraded to Hg2+. Increased concentrations of CH3Hg + were also observed, which was found to be due to impurities in the thimerosal.

  • 31.
    Roder, Friedrich
    et al.
    University of Osnabruck.
    Waichman, Sharon
    University of Osnabruck.
    Paterok, Dirk
    University of Osnabruck.
    Schubert, Robin
    University of Osnabruck.
    Richter, Christian
    University of Osnabruck.
    Liedberg, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics . Linköping University, The Institute of Technology.
    Piehler, Jacob
    University of Osnabruck.
    Reconstitution of Membrane Proteins into Polymer-Supported Membranes for Probing Diffusion and Interactions by Single Molecule Techniques2011In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 83, no 17, p. 6792-6799Article in journal (Refereed)
    Abstract [en]

    We have established a robust and versatile analytical platform for probing membrane protein function in a defined lipid environment on solid supports. This approach is based on vesicle capturing onto an ultrathin poly(ethylene glycol) (PEG) polymer brush functionalized with fatty acid moieties and subsequent vesicle fusion into a contiguous membrane. In order to ensure efficient formation of these tethered polymer-supported membranes (PSM), very small unilamellar vesicles (VSUV) containing fluorescent lipids or model transmembrane proteins were generated by detergent depletion with cyclodextrin. Thus, very rapid reconstitution of membrane proteins into PSM was possible in a format compatible with microfluidics. Moreover, surfaces could be regenerated with detergent solution and reused multiple times. Lipid and protein diffusion in these membranes was investigated by fluorescence recovery after photobleaching, single molecule tracking, and fluorescence correlation spectroscopy. Full mobility of lipids and a high degree of protein mobility as well as homogeneous diffusion of both were observed. Quantitative ligand binding studies by solid phase detection techniques confirmed functional integrity of a transmembrane receptor reconstituted into these PSM. Colocomotion of individual ligand-receptor complexes was detected, demonstrating the applicability for single molecule fluorescence techniques.

  • 32.
    Schymanski, Emma L
    et al.
    UFZ Helmholtz Centre Environm Research.
    Gallampois, Christine
    Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Health Sciences.
    Krauss, Martin
    UFZ Helmholtz Centre Environm Research.
    Meringer, Markus
    DLR German Aerosp Centre.
    Neumann, Steffen
    IPB Leibniz Institute Plant Biochem.
    Schulze, Tobias
    UFZ Helmholtz Centre Environm Research.
    Wolf, Sebastian
    IPB Leibniz Institute Plant Biochem.
    Brack, Werner
    UFZ Helmholtz Centre Environm Research.
    Consensus Structure Elucidation Combining GC/EI-MS, Structure Generation, and Calculated Properties2012In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 84, no 7, p. 3287-3295Article in journal (Refereed)
    Abstract [en]

    This article explores consensus structure elucidation on the basis of GC/EI-MS, structure generation, and calculated properties for unknown compounds. Candidate structures were generated using the molecular formula and substructure information obtained from GC/EI-MS spectra. Calculated properties were then used to score candidates according to a consensus approach, rather than altering or exclusion. Two mass spectral match calculations (MOLGEN-MS and MetFrag), retention behavior (Lee retention index/boiling point correlation, NIST Kovats retention index), octanol water partitioning behavior (log K-ow), and finally steric energy calculations were used to select candidates. A simple consensus scoring function was developed and tested on two unknown spectra detected in a mutagenic subfraction of a water sample from the Elbe River using GC/EI-MS. The top candidates proposed using the consensus scoring technique were purchased and confirmed analytically using GC/EI-MS and LC/MS/MS. Although the compounds identified were not responsible for the sample mutagenicity, the structure-generation-based identification for GC/EI-MS using calculated properties and consensus scoring was demonstrated to be applicable to real-world unknowns and suggests that the development of a similar strategy for multidimensional high-resolution MS could improve the outcomes of environmental and metabolomics studies.

  • 33.
    Sekretaryova, Alina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemical and Optical Sensor Systems. Linköping University, The Institute of Technology.
    Beni, Valerio
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, The Institute of Technology.
    Eriksson, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Chemical and Optical Sensor Systems. Linköping University, The Institute of Technology.
    Karyakin, Arkady A.
    Moscow MV Lomonosov State University, Russia.
    Turner, Anthony
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, The Institute of Technology.
    Vagin, Mikhail
    Linköping University, Department of Physics, Chemistry and Biology, Chemical and Optical Sensor Systems. Linköping University, The Institute of Technology.
    Cholesterol Self-Powered Biosensor2014In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 86, no 19, p. 9540-9547Article in journal (Refereed)
    Abstract [en]

    Monitoring the cholesterol level is of great importance, especially for people with high risk of developing heart disease. Here we report on reagentless cholesterol detection in human plasma with a novel single-enzyme, membrane-free, self-powered biosensor, in which both cathodic and anodic bioelectrocatalytic reactions are powered by the same substrate. Cholesterol oxidase was immobilized in a sol-gel matrix on both the cathode and the anode. Hydrogen peroxide, a product of the enzymatic conversion of cholesterol, was electrocatalytically reduced, by the use of Prussian blue, at the cathode. In parallel, cholesterol oxidation catalyzed by mediated cholesterol oxidase occurred at the anode. The analytical performance was assessed for both electrode systems separately. The combination of the two electrodes, formed on high surface-area carbon cloth electrodes, resulted in a self-powered biosensor with enhanced sensitivity (26.0 mA M-1 cm(-2)), compared to either of the two individual electrodes, and a dynamic range up to 4.1 mM cholesterol. Reagentless cholesterol detection with both electrochemical systems and with the self-powered biosensor was performed and the results were compared with the standard method of colorimetric cholesterol quantification.

  • 34.
    Sekretaryova, Alina N.
    et al.
    Chemistry and Material Science Faculties of M.V. Lomonosov Moscow State University, Moscow, Russia.
    Vokhmyanina, Darya V.
    Chemistry and Material Science Faculties of M.V. Lomonosov Moscow State University, Moscow, Russia.
    Chulanova, Tatyana O.
    Chemistry and Material Science Faculties of M.V. Lomonosov Moscow State University, Moscow, Russia.
    Karyakina, Elena E.
    Chemistry and Material Science Faculties of M.V. Lomonosov Moscow State University, Moscow, Russia.
    Karyakin, Arkady A.
    Chemistry and Material Science Faculties of M.V. Lomonosov Moscow State University, Moscow, Russia.
    Reagentless Biosensor Based on Glucose Oxidase Wired by the Mediator Freely Diffusing in Enzyme Containing Membrane2012In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 84, no 3, p. 1220-1223Article in journal (Refereed)
    Abstract [en]

    Wiring glucose oxidase in the membrane with an immobilized mediator is possible due to the diffusion ability of the latter, if the enzyme containing membrane is formed according to the proposed protocol, including exposing proteins to water–organic mixtures with the high content of organic solvent. In the course of the study, the new glucose oxidase mediator, unsubstituted phenothiazine, was discovered. The diffusion coefficient of the mediator in the resulting membrane is independent of the presence of enzyme. The cyclic voltammograms of the enzyme electrode after appearance of the only glucose in solution obtain a well-defined catalytic shape, which is normally observed for both the enzyme and the mediator in solution. Analytical performances of the resulting biosensor are comparable to the advanced second generation ones, which, however, require covalent linking of the mediator either to the membrane forming polymer or to the enzyme. Even without such covalent linking, the reported biosensor is characterized by an appropriate long-term operational stability allowing reagentless sensing.

  • 35.
    Sidstedt, Maja
    et al.
    Applied Microbiology, Department of Chemistry, Lund University, SE-221 00 Lund, Sweden; Swedish National Forensic Centre, SE-581 94 Linköping, Sweden.
    Romsos, Erica L
    Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8314, United States.
    Hedell, Ronny
    Swedish National Forensic Centre, SE-581 94 Linköping, Sweden; Department of Mathematical Sciences, Chalmers University of Technology and University of Gothenburg, SE-412 96 Gothenburg, Sweden.
    Ansell, Ricky
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering. Swedish National Forensic Centre, Linköping, Sweden.
    Steffen, Carolyn R
    Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8314, United States.
    Vallone, Peter M
    Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8314, United States.
    Rådström, Peter
    Applied Microbiology, Department of Chemistry, Lund University, SE-221 00 Lund, Sweden.
    Hedman, Johannes
    Applied Microbiology, Department of Chemistry, Lund University, SE-221 00 Lund, Sweden; Swedish National Forensic Centre, SE-581 94 Linköping, Sweden .
    Accurate Digital Polymerase Chain Reaction Quantification of Challenging Samples Applying Inhibitor-Tolerant DNA Polymerases.2017In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 89, no 3, p. 1642-1649Article in journal (Refereed)
    Abstract [en]

    Digital PCR (dPCR) enables absolute quantification of nucleic acids by partitioning of the sample into hundreds or thousands of minute reactions. By assuming a Poisson distribution for the number of DNA fragments present in each chamber, the DNA concentration is determined without the need for a standard curve. However, when analyzing nucleic acids from complex matrixes such as soil and blood, the dPCR quantification can be biased due to the presence of inhibitory compounds. In this study, we evaluated the impact of varying the DNA polymerase in chamber-based dPCR for both pure and impure samples using the common PCR inhibitor humic acid (HA) as a model. We compared the TaqMan Universal PCR Master Mix with two alternative DNA polymerases: ExTaq HS and Immolase. By using Bayesian modeling, we show that there is no difference among the tested DNA polymerases in terms of accuracy of absolute quantification for pure template samples, i.e., without HA present. For samples containing HA, there were great differences in performance: the TaqMan Universal PCR Master Mix failed to correctly quantify DNA with more than 13 pg/nL HA, whereas Immolase (1 U) could handle up to 375 pg/nL HA. Furthermore, we found that BSA had a moderate positive effect for the TaqMan Universal PCR Master Mix, enabling accurate quantification for 25 pg/nL HA. Increasing the amount of DNA polymerase from 1 to 5 U had a strong effect for ExTaq HS, elevating HA-tolerance four times. We also show that the average Cq values of positive reactions may be used as a measure of inhibition effects, e.g., to determine whether or not a dPCR quantification result is reliable. The statistical models developed to objectively analyze the data may also be applied in quality control. We conclude that the choice of DNA polymerase in dPCR is crucial for the accuracy of quantification when analyzing challenging samples.

  • 36.
    Subrahmanyam, S
    et al.
    Cranfield University, Institute Biosci and Technology, Silsoe MK45 4DT, Beds, England; .
    Piletsky, SA
    Cranfield University, Institute Biosci and Technology, Silsoe MK45 4DT, Beds, England; .
    Turner, APF
    Cranfield University, UK.
    Application of natural receptors in sensors and assays2002In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 74, no 16, p. 3942-3951Article in journal (Refereed)
    Abstract [en]

    Biosensors are analytical devices that use a biological or biologically derived material immobilized at a physicochemical transducer to measure one or more analytes. Although there are a large number of reviews on biosensors in general, there has been little systematic information. presented on the application of natural receptors in sensor technology. This perspective discusses broadly the fundamental properties of natural receptors; which make them an attractive option for use as biorecognition elements in. sensor technology. It analyses the current situation by reference to, typical examples, such as the application of nicotinic acetylcholine receptor and G protein-linked receptors in affinity sensors and analyses the problems that need to be resolved prior to any commercialization of such devices.

  • 37.
    Ulrich, Christian
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Andersson, Olof
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics . Linköping University, The Institute of Technology.
    Nyholm, Leif
    Uppsala University.
    Björefors , Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics . Linköping University, The Institute of Technology.
    Potential and Current Density Distributions at Electrodes Intended for Bipolar Patterning2009In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 81, no 1, p. 453-459Article in journal (Refereed)
    Abstract [en]

    This paper deals with the use of reaction gradients on bipolar electrodes for the patterning of electrode surfaces. More specifically, the potential and current density distributions in two setups containing bipolar electrodes were investigated to optimize and design specific gradient geometries. Comparisons with simulations based on simple conductivity models showed a good qualitative agreement, demonstrating that these models could be used to predict bipolar behavior in more complex setups. In conjunction with imaging surface plasmon resonance (iSPR) experiments, the reaction gradients on bipolar electrodes could further be visualized. It was, for example, found that the gradient in potential difference was approximately linearly distributed in the center of the bipolar electrode and that these potential differences could be determined using an ordinary Ag/AgCl reference electrode. The present results thus provide a better understanding of the processes relevant for bipolar patterning. This approach was finally used to generate a circular gradient region in a self-assembled monolayer, thereby showing the possibilities to create interesting substrates for biosensors and microarray applications.

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