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  • 1.
    Aghbolagh, Mahdi Shahmohammadi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Meynaq, Mohammad Yaser Khani
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shimizu, Kenichi
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Aspects on mediated glucose oxidation at a supported cubic phase2017In: Bioelectrochemistry, ISSN 1567-5394, E-ISSN 1878-562X, Vol. 118, p. 8-13Article in journal (Refereed)
    Abstract [en]

    A supported liquid crystalline cubic phase housing glucose oxidase on an electrode surface has been suggested as bio-anode in a biofuel. The purpose of this investigation is to clarify some aspect on the mediated enzymatic oxidation of glucose in such a bio-anode where the mediator ferrocene-carboxylic acid and glucose were dissolved in the solution. The enzyme glucose oxidase was housed in the water channels of the mono-olein cubic phase. The system was investigated with cyclic voltammetry at different scan rates and the temperature was varied between 15 degrees C and 30 degrees C. The diffusion coefficient of the mediator and also the film resistance was estimated showing a large decrease in the mass-transport properties as the temperature was decreased. The current from mediated oxidation of glucose at the electrode surface increased with decreasing film thickness. The transport of the mediator in the cubic phase was the rate-limiting step in the overall reaction, where the oxidation of glucose took place at the outer surface of the cubic phase.

  • 2.
    Ardlin, Berit I.
    et al.
    Umeå University, Faculty of Medicine, Department of Odontology.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Dahl, Jon E.
    Corrosion of dental nickel-aluminum bronze with a minor gold content-mechanism and biological impact2009In: Journal of Biomedical Materials Research. Part B - Applied biomaterials, ISSN 1552-4973, E-ISSN 1552-4981, Vol. 88B, no 2, p. 465-473Article in journal (Refereed)
    Abstract [en]

    Objectives: To study corrosion and to evaluate biological effects in vitro of corrosion products of a copper-aluminum-nickel alloy with 2% gold. Methods: The alloy NPGTM+2 with the nominal composition Cu:77.3; Al:7.8; Ni:4.3; Fe:3.0; Zn:2.7; Au:2.0; and Mn:1.7 was characterized. Static immersion in acidic saline, pH 2.2-2.4, was used to determine release of metallic elements in a milieu simulating the condition of plaque build-up in interproximal areas of the tooth. Corrosion and surface reactions in saline and artificial saliva were studied by electrochemical techniques including registration of open-circuit-potentials, polarization curves and impedance spectra. Extracts were made in cell culture media and acidic saline and used for MTT test for cytotoxicity and HET-CAM method for irritation. Results: The mean amount of elements released in the acidic saline were in g cm-2 : Cu:632; Al:210; Ni:144; Fe:122; Zn:48; Mn:52. No protective film was formed on the surface of the alloy, as extensive corrosion was observed in both saline and artificial saliva. The corrosion rate was higher in saline than in artificial saliva. Acidic extracts of the alloy diluted up to 64 times reduced cell viability with 80% or more. The extract induced coagulation of the blood vessels of the CAM and was rated as moderate irritant solution. Significance: The nickel-aluminum bronze showed high corrosion rate caused by an inability to create a protective surface layer. High levels of toxic elements were found after static immersion testing, and the corrosion products had a distinct adverse effect on the biological activity.

  • 3.
    Ardlin, Berit
    et al.
    Umeå University, Faculty of Medicine, Odontology, Dental Materials Science.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Chemistry.
    Effects of pH and Fluorides on Titanium2005In: Society for Biomaterials, 30th Annual Meeting & Exposition, Memphis,TN, USA: New Applications and Technologies, 2005Conference paper (Other academic)
    Abstract [en]

    Introduction: Titanium is used in dentistry both for crowns, fixed and removable partial dentures, suprastructures and for implants. In such applications, titanium may come in contact with fluorides. Prophylactic agents such as toothpastes and gels have effects on titanium that are dependent on their acidity and fluoride concentration. In order to obtain rapid bone growth and a strong bond between the implant and the bone, fluorides are used to modify the surfaces of titanium implants1. The aim of this investigation was to study the release of ions and the effects of fluorides on surfaces of titanium cp-II in saline solutions of different pF and pH using a) a brush test and b) electrochemical techniques including impedance spectroscopy2.

    Materials and Methods: Brush test. An electric toothbrush was used to brush the titanium electrodes for 2 min in aqua solutions of 0.9 % NaCl with 0, 0.3, 0.6 and 1 % NaF. The pH of the solutions was adjusted by adding ultra pure HNO3 and 1 M NaOH. In order to avoid interference with the chemical analyses, the solutions were not buffered. The solutions were divided into two all-embracing groups, pH 4.5 and pH>5.3, with respect to their acidity. An atomic absorption spectrophotometer equipped with a graphite atomizer with Zeeman effect background correction was used to detect titanium in the NaCl solutions.

    Electrochemical tests. Planar titanium electrodes with surface area of 0.28 cm2 served as working electrodes and were wet-ground with SiC paper through 1200 grit using standard metallographic procedures prior to exposure to the various electrolyte solutions. The solutions employed were similar to those used in the previous experiments, i.e. phosphate-buffered 0.9 % NaCl solutions with a pH between 4 and 7, containing 0, 0.3, 0.6 and 1 % NaF. An ordinary three-electrode setup was used with Ag/AgCl, sat KCl as a reference electrode and a platinum sheet as a counter electrode. The open circuit potential was recorded for 18–20 hours, and the electrode was then polarized to –0.18 V vs. ref. for five minutes. After this an impedance spectrum was recorded at –0.18 V vs. ref in the frequency range 100 000 Hz to 5 mHz and an amplitude of 10 mV peak to peak. Finally a linear anodic polarization curve was recorded from –0.5 V to 1 V vs ref at a sweep rate of 2 mV/sec.

    Results: The result of the brush tests is shown in Table 1. The highest amount of titanium was detected in the NaCl solutions with 0.6 or 1.0 % NaF at pH 4.5.

    Titanium remains passive in neutral solutions irrespective of the addition of fluoride and also at pH 4 without addition of fluoride. This is indicated in all three electrochemical experiments: the final electrode potential at open circuit is around -0.1 V vs ref after 18 hours, the impedance spectrum shows an almost pure capacitive behavior and the current at anodic polarization is very small. At low pH with addition of fluoride, titanium becomes active, as evidenced by a negative final electrode potential at open circuit of around -1.0 V vs ref after 18 hours, an impedance spectrum indicating a non-blocking electrode and a high current at anodic polarization. At medium pH and with an addition of fluoride the electrochemical experiments indicate the formation of a porous non-passivating surface film. In the latter case the final open circuit potential is around -0,5 V vs ref, the impedance spectra show a non-blocking electrode with a large charge-storing capacity and the current at anodic polarization is close to the values obtained for the active electrode at pH 4. The results of the electrochemical tests are summarized in Table 2

  • 4.
    Ardlin, Berit
    et al.
    Umeå University, Faculty of Medicine, Odontology.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Chemistry.
    Dahl, Jon E.
    Corrosion and Irritation Tests of a Dental Aluminum Bronze2006In: International Association for Dental Research, 84th General Session & Exhibition, Brisbane, Australia, 2006Conference paper (Refereed)
    Abstract [en]

    Corrosion and irritation tests of a dental aluminium bronze. B.I. ARDLIN*1,2, B. LINDHOLM-SETHSON1 and J.E. DAHL2, 1Umeå University, Sweden, 2NIOM – Nordic Institute of Dental Materials, Haslum, Norway

    Objectives: The aims of this investigation were to study the corrosion of a copper-aluminium-nickel alloy for fixed prostheses, and to evaluate possible irritant effects of the corrosion products.

    Methods: The alloy NPG+2 with the nominal composition Cu:77.3; Al:7.8; Ni:4.3; Fe:3.0; Zn:2.7; Au:2.0; Mn:1.7, was characterized. Static immersion in saline lactic acid solution was selected to quantify metallic elements released in a milieu simulating the condition of plaque build-up in interproximal areas. Corrosion and surface reactions in artificial saliva and saline solutions were studied by electrochemical techniques including registration of polarization curves and impedance spectra. Irritative effect of the corrosion products was assed by the Hen’s egg test-chorio-allantoic membrane, HET-CAM.

    Results: Immersion test. The following metal elements were found in the saline lactic acid solutions after immersion of two specimens for 7 days (specimen 1 / specimen 2 in g cm-2): Cu (769/494); Al (249/172); Ni (164/124), Fe (134/109); Zn (59/37); and Mn (61/43). Electrochemical tests. Higher corrosion rates were found in the saline solution, pH 4 or pH 7, than in the aerated or de-aerated artificial saliva solution. No high-quality passive film was formed on the studied alloy as extensive corrosion was observed on test specimens in both solutions. HET CAM. The saline lactic acid extracts induced coagulation of the blood vessels of the chorio-allantoic membrane after an average time of 1 min and the alloy was rated as a moderate irritant.

    Conclusions: The copper-aluminium-nickel alloy investigated in this study showed high corrosion caused by an inability to create a stable passivating surface layer. High levels of the elements Cu, Al, Ni, Fe, Zn and Mn were found by static immersion testing, and the corrosion products had an irritant effect.

    The project was supported by grants from the European Union Structure Foundation Objective One.

  • 5.
    Bodén, Ida
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Surgery. Umeå University, Faculty of Science and Technology, Centre for Biomedical Engineering and Physics (CMTF).
    Larsson, William
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nilsson, David
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Forssell, Erik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Naredi, Peter
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Surgery.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Centre for Biomedical Engineering and Physics (CMTF).
    In vivo skin measurements with a novel probe head for simultaneous skin impedance and near-infrared spectroscopy2011In: Skin research and technology, ISSN 0909-752X, E-ISSN 1600-0846, Vol. 17, no 4, p. 494-504Article in journal (Refereed)
    Abstract [en]

    Background/purpose: Near-infrared (NIR) spectroscopy and skin impedance (IMP) measurements are useful techniques for objective diagnostics of various skin diseases. Here, we present a combined probe head for simultaneous, time-saving NIR spectroscopy and skin impedance measurements. The probe also ensures that both measurements are performed under equal conditions and at the same skin location.

    Methods: Finite element method simulations were performed for evaluation of the impedance. In vivo skin measurements were performed and combined NIR and impedance spectra were analysed by means of multivariate methods with respect to body location, age and gender. The classification rate was determined by a planar discriminant analysis. Reproducibility was investigated by calculation of scatter values and statistical significance between overlapping groups was assessed by the calculation of intra-model distances, q.

    Results: The novel probe yielded rapid reproducible results and was easy to manage. Significant differences between skin locations and to a lesser extent age groups and gender were demonstrated.

    Conclusion: With the novel probe, statistically significant differences between overlapping classes in score plots can be confirmed by calculating intra-model distances. The influence of molecular differences in the skin at different body locations is larger than the influence of gender or age and therefore relevant reference measurements are discussed.

  • 6.
    Bodén, Ida
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Surgery.
    Nilsson, David
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Naredi, Peter
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Surgery.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Centre for Biomedical Engineering and Physics (CMTF).
    Characterization of healthy skin using near infrared spectroscopy and skin impedance2008In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 46, no 10, p. 985-995Article in journal (Refereed)
    Abstract [en]

    Near infrared spectroscopy (NIR) and skin impedance (IMP) spectroscopy are two methods suggested for diagnoses of diseases inducing adverse effects in skin. The reproducibility of these methods and their potential value in non-invasive diagnostics were investigated. Measurements were performed in vivo on healthy skin at five anatomic body sites on eight young women. partial least squares discriminant analysis showed that both methods were useful for classification of the skin characteristics at the sites. Inter-individually the NIR model gave 100% correct classification while the IMP model provided 92%. Intra-individually the NIR model gave 88% correct classification whereas the IMP model did not provide any useful classification. The correct classification was increased to 93% when both datasets were combined, which demonstrates the value of adding information. Partial least squares discriminant analysis gave 72% correct predictions of skin sites while the combined model slightly improved to 73%.

  • 7.
    Bodén, Ida
    et al.
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Surgery. Umeå University, Faculty of Science and Technology, Centre for Biomedical Engineering and Physics (CMTF).
    Nyström, Josefina
    Swedish University of Agricultural Sciences, Unit of Biomass Technology and Chemistry.
    Geladi, Paul
    Swedish University of Agricultural Sciences, Unit of Biomass Technology and Chemistry.
    Naredi, Peter
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Surgery.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    NIR and skin impedance spectroscopic measurements for studying the effect of coffee and alcohol on skin, and dysplastic naevi2012In: Skin research and technology, ISSN 0909-752X, E-ISSN 1600-0846, Vol. 18, no 4, p. 486-494Article in journal (Refereed)
    Abstract [en]

    Background/purpose: Near infrared (NIR) and impedance spectroscopy can be used for clinical skin measurements and need to be evaluated for possible confounding factors; (a) are skin conditions of the patient and the subsequent skin measurements influenced by alcohol and/or coffee consumption and (b) are measurements of dysplastic naevi (DN) reproducible over time and significantly different compared to reference skin.

    Methods: NIR and skin impedance spectroscopic data were analysed multivariately. In the first study, the skin characteristics of 15 healthy individuals were examined related to body location, gender, individual differences, and consumption of coffee or alcohol. The second study included five patients diagnosed with dysplastic naevi syndrome (DNS). Measurements were taken on DN and reference skin over time.

    Results: In the first study, body location and gender had a major influence on measurement scores. Inter-individual skin characteristics and coffee or alcohol effects on skin characteristics were of minor importance. In the second study, it was shown that DN can be differentiated from reference skin and the measurements are stable over time.

    Conclusions: Moderate consumption of alcohol and coffee did not influence the results of the measurements. It is possible to follow, stable or changed, characteristics of DN over time.

  • 8.
    Bodén, Ida
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Surgery.
    Nyström, Josefina
    Swedish University of Agricultural Sciences, Unit of Biomass Technology and Chemistry.
    Lundskog, Bertil
    Umeå University, Faculty of Medicine, Department of Medical Biosciences, Pathology.
    Zazo, Virginia
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Dermatology and Venerology.
    Geladi, Paul
    Swedish University of Agricultural Sciences, Unit of Biomass Technology and Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Naredi, Peter
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Surgery.
    Non-invasive identification of melanoma with near-infrared and skin impedance spectroscopy2013In: Skin research and technology, ISSN 0909-752X, E-ISSN 1600-0846, Vol. 19, no 1, p. e473-e478Article in journal (Refereed)
    Abstract [en]

    Background/purpose: An early diagnosis of cutaneous malignant melanoma is of high importance for good prognosis. An objective, non-invasive instrument could improve the diagnostic accuracy of melanoma and decrease unnecessary biopsies. The aim of this study was to investigate the use of Near infrared and skin impedance spectroscopy in combination as a tool to distinguish between malignant and benign skin tumours.

    Methods: Near infrared and skin impedance spectra were collected in vivo on 50 naevi or suspect melanomas prior to excision. Received data was analysed with multivariate techniques and the results were compared to histopathology analyses of the tumours. A total of 12 cutaneous malignant melanomas, 19 dysplastic naevi and 19 benign naevi were included in the study.

    Results: The observed sensitivity and specificity of the proposed method were 83% and 95%, respectively, for malignant melanoma.

    Conclusions: The results indicate that the combination of near infrared and skin impedance spectroscopy is a promising tool for non-invasive diagnosis of suspect cutaneous malignant melanomas. 

  • 9. Geladi, Paul
    et al.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Chemistry.
    Nyström, Josefina
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lillhonga, Tom
    Lestander, Torbjörn
    Burger, Jim
    Chemometrics in spectroscopy: Part 2. Examples2004In: SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY, ISSN 0584-8547, Vol. 59, no 9, p. 1347-57Article in journal (Refereed)
    Abstract [en]

    Some of the principles and main methods of chemometrics are illustrated by examples. The examples are from electrochemistry, process analytical chemistry and multivariate imaging. Principal component analysis, partial least squares regression and multivariate image analysis are used to illustrate the power of chemometrical thinking. The emphasis is on plotting and visualization for showing the salient features of a model or data set.

  • 10. Geladi, Paul
    et al.
    Nelson, Andrew
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Chemistry.
    Complex numbers in chemometrics: Examples from multivariate impedance measurements on lipid monolayers2007In: Analytica Chimica Acta, Vol. 595, no 1-2, p. 152-9Article in journal (Refereed)
    Abstract [en]

    Electrical impedance gives multivariate complex number data as results. Two examples of multivariate electrical impedance data measured on lipid monolayers in different solutions give rise to matrices (16 × 50 and 38 × 50) of complex numbers. Multivariate data analysis by principal component analysis (PCA) or singular value decomposition (SVD) can be used for complex data and the necessary equations are given. The scores and loadings obtained are vectors of complex numbers. It is shown that the complex number PCA and SVD are better at concentrating information in a few components than the naïve juxtaposition method and that Argand diagrams can replace score and loading plots. Different concentrations of Magainin and Gramicidin A give different responses and also the role of the electrolyte medium can be studied. An interaction of Gramicidin A in the solution with the monolayer over time can be observed.

  • 11.
    Geladi, Paul
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nyström, Josefina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Eriksson, Jan W
    Nilsson, Anders
    Lithner, Folke
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    A multivariate NIR study of skin alterations in diabetic patients as compared to control subjects2000In: Journal of Near Infrared Spectroscopy, ISSN 0967-0335, E-ISSN 1751-6552, Vol. 8, no 4, p. 217-227Article in journal (Refereed)
    Abstract [en]

    A group of 15 diabetic persons with different degrees of diabetes complications, including skin changes, was studied by Fourier Transform Near Infrared (FT-NIR) spectroscopy. Skin reflectance spectra were measured with a fibre-optic probe in four locations (sites): hand, arm, leg and foot. For reference, a group of 28 healthy controls was also measured. Multivariate analysis of the NIR spectra obtained shows a high potential for classification and discrimination of the skin conditions. Valuable indications for future experiments can be observed.

  • 12. Hägerlind, E
    et al.
    Falk, M
    Löfstedt, T
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bodén, I
    Near infrared and skin impedance spectroscopy: a possible support in the diagnostic process of skin tumours in primary health care2015In: Skin research and technology, ISSN 0909-752X, E-ISSN 1600-0846, Vol. 21, no 4, p. 493-499Article in journal (Refereed)
    Abstract [en]

    Background/purpose: The global incidence of skin cancer has increased drastically in recent decades, especially in Australia and Northern Europe. Early detection is crucial for good prognosis and high survival rates. In general, primary care physicians have considerably lower sensitivity and specificity rates for detection of skin cancer, compared to dermatologists. A probable main reason for this is that current diagnostic tools are subjective in nature, and therefore diagnostic skills highly depend on experience. Illustratively, in Sweden, approximately 155500 benign skin lesions are excised unnecessarily every year. An objective instrument, added to the clinical examination, might improve the diagnostic accuracy, and thus promote earlier detection of malignant skin tumours, as well as reduce medical costs associated with unnecessary biopsies and excisions. The general aim of this study was to investigate the usefulness of the combination of near infrared (NIR) and skin impedance spectroscopy as a supportive tool in the diagnosis and evaluation of skin tumours in primary health care. Methods: Near infrared and skin impedance data were collected by performing measurements on suspect malignant, premalignant and benign tumours in the skin of patients seeking primary health care for skin tumour evaluation. The obtained data were analysed using multivariate analysis and compared with the diagnosis received by the conventional diagnostic process. Results: The observed sensitivity and specificity rates were both 100%, when discriminating malignant and premalignant skin tumours from benign skin tumours, and the observed sensitivity and specificity for separating malignant skin tumours from premalignant and benign skin tumours were also 100%, respectively. Conclusion: The results of this study indicate that the NIR and skin impedance spectroscopy may be a useful supportive tool for the general practitioner in the diagnosis and evaluation of skin tumours in primary health care, as a complement to the visual assessment.

  • 13.
    Khani Meynaq, Mohammad Yaser
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tesfalidet, Solomon
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Cationic Interaction with Phosphatidylcholine in a lipid cubic phase studied with electrochemical impedance spectroscopy and Small Angle X-ray Scattering2018In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 528, p. 321-329Article in journal (Refereed)
    Abstract [en]

    Hypothesis: Electrochemical Impedance Spectroscopy (EIS) can be used to investigate cationic interaction with the choline headgroup in the ternary system of monoolein/dioleoylphosphatidylcholine/water (MO/DOPC/H2O).

    Experiments: EIS was used to estimate the resistance and capacitance of a freestanding membrane of a lipid cubic phase (LCP). The membrane was formed in a small cylindrical aperture separating two compartments, containing one Pt electrode each. The impedance experiments were carried out in a two electrode setup with electrolyte solutions made of KCl, CsCl, MgCl2 and CaCl2 filling the compartments at two different ionic strength. Small angle X-ray diffraction (SAXRD) was used to establish the structure and cell unit parameters of the LCP.

    Findings: The interpretation of ionic interaction with phosphatidylcholine was based on estimated membrane resistances and capacitances from EIS measurements. The magnitude of cationic interaction with the lipid headgroup in the water channels is correlated to the membrane resistance that increases in the order Cs+ < K+ < Mg2+ < Ca2+ following the Hofmeister direct series and also reflecting the order of intrinsic binding constants. The membrane capacitance and SAXRD results are discussed as an effect of cationic interaction and it was possible to observe both swelling and condensing effects. The stability of the cubic phase throughout the experiments was confirmed by SAXRD.

  • 14.
    Khani Meynaq, Mohammad Yaser
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shimizu, Kenichi
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Physical and Theoretical Chemistry Laboratory, Department of Chemistry, Oxford University, Oxford, United Kingdom.
    Aghbolagh, Mahdi Shahmohammadi
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tesfalidet, Solomon
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Investigation of metal ion interaction with a lipid cubic phase using electrochemical impedance spectroscopy2016In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 482, p. 212-220Article in journal (Refereed)
    Abstract [en]

    AbstractHypothesis Electrochemical impedance spectroscopy, EIS, can be used as a complementary technique to investigate ion interaction with the headgroup region in the aqueous channels of a lipid cubic phase, LCP. Experiments A freestanding membrane made of monoolein LCP was formed by filling a small aperture that separates two cell compartments. The cell compartments were filled with electrolyte solutions at two different ionic strengths: i.e.: 10 and 100 mM, of KCl, CsBr and CaCl2. Electrochemical impedance spectroscopy was recorded between two platinum electrodes that were present at each side of the membrane. Findings The membrane resistance and capacitance were estimated from equivalent circuit fitting of the impedance data. It was confirmed that calcium ions interacts strongly with the headgroup region in the aqueous channels giving significantly higher membrane resistances compared to monovalent alkali metal ions. The membrane capacitance with Ca2+(aq) in solution was concentration dependent, which for the first time indicates formation of two different cubic phases at these conditions.

  • 15. Krupinska, Karolina
    et al.
    Geladi, Paul
    Vikholm-Lundin, Inger
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Detection of low levels of Escherichia coli by electrochemical impedance spectroscopy and singular value decomposition2017In: Chemometrics and Intelligent Laboratory Systems, ISSN 0169-7439, E-ISSN 1873-3239, Vol. 163, p. 49-54Article in journal (Refereed)
    Abstract [en]

    The first steps are reported in the development of a new ultrasensitive electrochemical biosensor for detection of Escherichia coli (E. coli) in water. Two gold electrodes in a sandwich flow-cell were modified with E. coli polyclonal antibody and exposed to three different concentrations of E. coli. Electrochemical Impedance Spectroscopy was used in combination with Singular Value Decompostion of the complex numbers to monitor the interactions at the electrode surfaces. A linear regression line in the concentration range 10-1000 CFU⁎ml-1 was obtained without use of redox probes or metal nanoparticles for signal amplification.

  • 16.
    Lindholm-Sethson, Britta
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ardlin, Berit
    Umeå University, Faculty of Medicine, Department of Odontology, Dental Materials Science.
    Effects of pH and fluoride concentration on the corrosion of titanium2008In: Journal of Biomedical Materials Research Part A, ISSN 1549-3296, Vol. 86A, no 1, p. 149-159Article in journal (Refereed)
    Abstract [en]

    The aim of this investigation was to confirm and summarize the corrosion behavior of titanium in saline solution at different pH and fluoride concentration, and to characterize the surface films and the stability of a passive and aged titanium surface using open circuit potential measurements, electrochemical impedance spectroscopy, and anodic polarization curves. The results from the electrochemical measurements were related to titanium released after 2-min brushing with saline solutions with different pH and fluoride concentration, that is, simulating tooth brushing with fluoride containing prophylactic substances. Titanium was analyzed using atomic adsorption spectrophotometry. The pH in the saline solution was varied between 4 and 7 with additions of sodium fluoride up to 1.0 wt %. The presence of fluoride in solution was unfavorable for the stability of titanium and led to corrosion and the release of titanium especially at low pH. The combination of low pH and presence of fluoride ions in solution destroyed a passive film on the titanium surface even after aging for 170 h in neutral saline solution. The results do not necessarily imply the occurrence of biological soft tissue related effects even if a physical contact between titanium and the surrounding milieu is prevalent. To provide a general understanding of electrochemical techniques in biomaterial research, much effort was put in the qualitative description of the results, with the intention to provide a broader understanding of especially the impedance method to other researchers. (c) 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007.

  • 17.
    Lindholm-Sethson, Britta
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Ardlin, Berit
    Umeå University, Faculty of Medicine, Odontology.
    Electrochemical investigation of two dental metals. Unalloyed titanium and copper - aluminium alloy2006In: The European Society for Electroanalytical Chemistry, 2006Conference paper (Other academic)
    Abstract [en]

    Titanium is used in dentistry in many applications: crowns, fixed and removable partial dentures, suprastructures and implants. In these functions, titanium may get in contact with prophylactic agents such as toothpastes and gels that contain fluorides.

    Dental copper-based alloys have become popular for crowns and fix prostheses in some countries, mostly because they have a gold-like appearance and are much less expensive than gold alloys. The accessibility of copper-based alloys is increasing and they are now available in Western Europe and US, but the discussion of their biocompatibility continues. It has been advocated that the alloys should not be generally used in dentistry.

    The aim of this investigation was to:

    • study the effects of fluorides on surfaces of titanium cp-II in saline solutions with different pF and pH using electrochemical techniques

    • study various aspects of corrosion of a copper-aluminium alloy in saline and artificial saliva using electrochemical techniques.

    The electrochemical techniques used were recording of open circuit potential, anodic polarisation and electrochemical impedance. Inductively coupled plasma spectroscopy of lactic acid saline extracts was also used.

    The results clearly show that titanium does not maintain its passivating properties in an acidic environment containing fluorides and that the copper-based alloy is an active corrosion state in the chloride containing electrolyte solutions; either saline or artificial saliva.

  • 18.
    Lindholm-Sethson, Britta
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Geladi, Paul
    Koeppe II, Roger E
    Jonsson, Oskar
    Nilsson, David
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nelson, Andrew
    Multivariate Data Analysis for Enhanced Interpretation of Electrochemical Impedance Spectra of Gramicidin-Ion Interactions in Phospholipid Monolayers2007In: Langmuir, Vol. 23, no 9, p. 5029-32Article in journal (Refereed)
    Abstract [en]

    This article describes a multifrequency electrochemical impedance study of phospholipid monolayers on a mercury drop electrode in solutions containing electrolytes and gramicidin derivatives: gramicidin A (gA), gramicidin-BOC (g-BOC), and desformylgramicidin (g-des). The impedance spectra have been studied individually (univariate approach) and also transformed using a multivariate data reduction method (multivariate approach). It was shown that the two approaches are complementary. Thus the formation of K+-conducting channels is observed in gA only, and these channels can be distinguished from an interaction of all gramicidin derivatives with Mg2+. An unknown peptide interaction in the monolayer was observed on a slow time scale.

  • 19.
    Lindholm-Sethson, Britta
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Geladi, Paul
    Umeå University, Faculty of Science and Technology, Chemistry.
    Nelson, Andrew
    Interaction with a phospholipid monolayer on a mercury electrode Multivariate analysis of impedance data2001In: Analytica Chimica Acta, Vol. 446, no 1-2, p. 121-30Article in journal (Refereed)
    Abstract [en]

    Dioleyl phosphatidylcholine (DOPC) monolayer coated mercury electrodes were investigated with electrochemical impedance spectroscopy. The data from experiments with coated electrodes in contact with different electrolytes was analysed with principal component analysis and regression methods to characterise the significant features of the various impedance spectra. It is shown by combining multivariate analysis and electrochemical impedance spectroscopy that it is possible to differentiate between the various spectra from measurements in KCl, NaCl, CsCl, and LiCl, respectively. Some aspects of drug interaction, doxorubicin, with the monolayer are also discussed.

  • 20.
    Lindholm-Sethson, Britta
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry. Centre for Biomedical Engineering and Physics.
    Nyström, Josefina
    Umeå University, Faculty of Science and Technology, Chemistry. Centre for Biomedical Engineering and Physics.
    Geladi, Paul
    Koeppe, Roger
    Nelson, Andrew
    Whitehouse, Conor
    Are biosensor arrays in one membrane possible? A combination of multifrequency impedance measurements and chemometrics2003In: Analytical and Bioanalytical Chemistry, Vol. 377, no 3, p. 478-85Article in journal (Refereed)
    Abstract [en]

    A novel concept of a membrane-based micro-array biosensor is presented. The methodology is based on a single lipid membrane interrogated with electrochemical impedance techniques followed by multivariate data analysis. A single membrane is designed so that relaxation processes with a range of time constants can be probed at different potentials. A range of other approaches cited in the literature is reviewed.

  • 21.
    Lindholm-Sethson, Britta
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Nyström, Josefina
    Umeå University, Faculty of Science and Technology, Chemistry.
    Geladi, Paul
    Nelson, Andrew
    Gramicidin A interaction at a dioleoyl phosphatidylcholine monolayer on a mercury drop electrode2003In: Analytical and Bioanalytical Chemistry, Vol. 375, no 3, p. 350-5Article in journal (Refereed)
    Abstract [en]

    A biosensor where the sensing surface is a fluid dioleyl phosphatidylcholine monolayer (DOPC) deposited on a mercury drop was used. The lipid monolayer was held in 0.1 M NaCl and a concentration of gramicidin A in the range 0-12 nM was used. Electrochemical impedance spectroscopy in the frequency range 0.1-65 kHz was employed to investigate how the defect-free monolayer responds to interactions of gramicidin A in solution.

    The data was analyzed both with multivariate data analysis and classical electrochemical methods. The principal component analysis of the resulting impedance spectra gave a linear dependence on the concentration of gramicidin A. An increasing permittivity was observed in the low-frequency regime with increasing concentration of gramicidin A in solution.

  • 22.
    Lindholm-Sethson, Britta
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nyström, Josefina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Malmsten, Martin
    Department of Pharmacy, Uppsala University.
    Ringstad, Lovisa
    Department of Pharmacy, Uppsala University.
    Nelson, Andrew
    Centre for Molecular Nanoscience, School of Chemistry, University of Leeds, Leeds, United Kingdom.
    Geladi, Paul
    Unit of Biomass Technology and Chemistry, SLU, Umeå, Sweden.
    Electrochemical impedance spectroscopy in label-free biosensor applications: multivariate data analysis for an objective interpretation2010In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642, E-ISSN 1618-2650, Vol. 398, no 6, p. 2341-9Article in journal (Refereed)
    Abstract [en]

    Electrochemical impedance spectroscopy plays an important role in biosensor science thanks to the possibility of finding specific information from processes with different kinetics at a chosen electrode potential in one experiment. In this paper we briefly discuss label-free impedimetric biosensors described in the literature. A novel method for neutral interpretation of impedance data is presented that includes complex number chemometrics. Three examples are given based on impedance measurements on synthetic biomembranes, in this case a lipid monolayer deposited on a mercury electrode. The interaction of various compounds with the monomolecular lipid layer is illustrated with the following: (1) different concentrations of magainin (Geladi et al. in Proc. Int. Fed. Med. Biomed. Eng. 9:219-220, 2005); (2) different derivatives of gramicidin A (Lindholm-Sethson et al. in Langmuir 24:5029-5032, 2007), and (3) an antimicrobial peptide (Ringstad et al. in Langmuir 24:208-216, 2008).

  • 23.
    Meynaq, Mohammad Yaser Khani
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tesfalidet, Solomon
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Interaction of anions with lipid cubic phase membranes, an electrochemical impedance study2018In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 528, p. 263-270Article in journal (Refereed)
    Abstract [en]

    Hypothesis: Electrochemical impedance spectroscopy is useful to monitor anionic interactions with a Lipid Cubic Phase, as previously demonstrated for cationic interaction (Khani Meynaq et al., 2016). It was expected that the smaller hydrophilic anions, acetate and chloride, would interact differently than the large tryptophan anion with its hydrophobic tail.

    Experiment: The impedance measurements enabled estimation of resistances and capacitances of a freestanding lipid cubic phase membrane at exposure to 4 and 40 mM solutions of NaCl, NaOAc and NaTrp. Small-angle X-ray scattering was used for cubic phase identification and to track structural changes within the cubic phase when exposed to the different electrolytes.

    Findings: The membrane resistance increases at exposure to the electrolytes in the order Cl− < OAc− < Trp−. The membrane resistance decreases with time at exposure to the hydrophilic anions and increases with time at Trp− exposure. The membrane capacitances were lower for NaTrp compared to NaCl and NaOAc at the corresponding concentrations which is consistent with the results from SAXRD. It is concluded that Trp− ions do not enter the aqueous channels of the cubic phase but are strongly adsorbed to the membrane/electrolyte interface leading to large alteration of the lipid phase structure and a high membrane resistance.

  • 24. Nazaruk, Ewa
    et al.
    Bilewicz, Renata
    Lindblom, Göran
    Umeå University, Faculty of Science and Technology, Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Chemistry. Centre for Biomedical Engineering and Physics.
    Cubic phases in biosensing systems2008In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642 (Print) 1618-2650 (Online), Vol. 391, no 5, p. 1569-78Article in journal (Refereed)
    Abstract [en]

    Incorporation of membrane proteins with retained activity in artificial membranes for use in membrane-based sensors has attracted scientists for decades. This review briefly summarises general concepts on relevant cubic phases with and without incorporated proteins and provides some insight into the development of biosensors where bicontinuous cubic phases are used for incorporation of an enzyme. Some new data on impedance characterisation of a supported cubic phase are also shown. An efficient membrane-based electrochemical biosensor requires that the analyte has free access to the immobilised membrane protein and that regeneration of the catalysing enzyme is fast. Long-term stability of the system is also necessary for the biosensor to find applications outside the research laboratory. These basic concepts are discussed in the review along with presentation of those biosensing systems based on cubic phases that are reported in the literature.

  • 25.
    Nyström, Josefina
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Geladi, Paul
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Chemistry.
    Larson, Johan
    Umeå University, Faculty of Medicine, Radiation Sciences, Oncology.
    Svensk, Ann-Christin
    Umeå University, Faculty of Medicine, Radiation Sciences, Oncology.
    Franzén, Lars
    Umeå University, Faculty of Medicine, Radiation Sciences, Oncology.
    Objective measurement of Radiation Induced Erythema by nonparametric hypothesis testing on indices from multivariate data2008In: Chemometrics and Intelligent Laboratory Systems, Vol. 90, no 1, p. 43-8Article in journal (Refereed)
    Abstract [en]

    Three instrumental measurement techniques: Laser-Doppler Imaging (LDI), Digital Colour Photography (DCP) and Near InfraRed (NIR) spectroscopy were tested for their potential to objectively measure radiation-based erythema in breast cancer patients. The irradiation dose intervals were 0, 8-16, 18-26, 28-34, 36-44 and 46-50 Gy. In addition, two types of skin lotion for reducing erythema were tested on the patients and these were compared to using no lotion. The measured results had very skew distributions for all three techniques making nonparametric testing necessary. The Wilcoxon Signed Rank Sum Test (WSRST) was used for this purpose. LDI was performed to produce univariate average perfusion values leading to a perfusion increment ratio. These ratios showed a good sensitivity to erythema, with a median detection limit of 18 Gy. DCP was used to extract average red-green-blue (RGB) values that were used in multivariate models. Results for a combination of principal component score values showed a marked increase in median erythema from 8 Gy on. The Multivariate data from NIR spectroscopy were data-reduced to principal component scores and combinations of these were tested. The score combinations were used to show median detection limits down to 8 Gy. The difference between the lotions and using no lotion gave no significant result for the WSRST paired comparison for any used measurement technique.

  • 26.
    Nyström, Josefina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Geladi, Paul
    Unit of Biomass Technology and Chemistry, SLU Röbäcksdalen, Umeå, Sweden, .
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Rattfelt, Jenny
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Svensk, Ann-Christin
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
    Franzén, Lars
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
    Objective measurements of radiotherapy-induced erythema2004In: Skin research and technology, ISSN 0909-752X, E-ISSN 1600-0846, Vol. 10, no 4, p. 242-250Article in journal (Refereed)
    Abstract [en]

    Background/aims: The development of acute radiation erythema is a common phenomenon among patients undergoing radiotherapy treatment. Because of the absence of reliable objective classification methods, the degree of skin reaction can at present mainly be judged subjectively in the clinic. This has motivated the present preliminary study, concerning the first steps in the development of an objective method for skin reaction classification.

    Methods: Three non-invasive techniques were used: near-infrared (NIR) spectroscopy, laser Doppler perfusion imaging and digital photography. The NIR spectra were analysed with principal component analysis (PCA), and the results from the other two with traditional univariate methods. Measurements were made on breast cancer patients who had been exposed to different irradiation doses. A total of 28 breast cancer patients participated one to three times each; 12 were treated with photons at 4 or 6 MeV and 16 were treated with high-energy electrons between 10 and 20 MeV to a maximum dose of 50 Gy.

    Results: PCA of NIR spectra shows that information on radiation dose lies mainly in the first principal component. It is observed that the higher the dose the higher the score value. The results from the laser Doppler measurements show that in 79% of the cases the perfusion increases significantly with radiation dose. Analysis of the digital photography shows that a proposed skin redness index (SRI), increases with a higher radiation dose. However, the increase in most cases is not significant. By combining all data, correlation to radiation doses was seen for 74% of the patients who participated more than once.

    Conclusion: All three non-invasive methods correlate with the radiation dose but to various degrees. NIR spectroscopy, laser Doppler and a combination of the three techniques are the most promising methods for characterising erythema

  • 27.
    Nyström, Josefina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Geladi, Paul
    NOPAPROD non-parametric testing on projections from multivariate data: Applications to near infrared spectroscopy in clinical studies2009In: Journal of Near Infrared Spectroscopy, ISSN 0967-0335, E-ISSN 1751-6552, Vol. 17, no 2, p. 101-107Article in journal (Refereed)
    Abstract [en]

    Clinical studies may be carried out using non-invasively collected near infrared spectra of patient skin. Two problems encountered are: (1) data reduction to go from thousands of wavelengths to some clinically relevant estimator and (2) getting statistical significance from noisy data with sometimes very skewed distributions. The problem of data reduction can usually be solved by principal component analysis to get a few meaningful components. In the space spanned by these components, a direction of discrimination may have to be found, typically discrimination between treated and control. A visual difference in a score plot is often not enough; statistical significance has to be demonstrated. Once a univariate estimator is found, non-parametric testing can show significant differences, even if the data are noisy and have an unknown and skewed distribution. The NOPRAPOD method combines the actions of finding a direction in a reduced data space and performing the non-parametric significance testing by producing a disk of significance. Two examples are included. Example one is from a study of diabetes-related neuropathy where it is shown that significant differences show up in the NIR spectra. Example two is from a study of post-operative radiation treatment of breast cancer patients, where it is shown that radiation effects (erythema) and the effect of lotion can be determined with an indication of significance from the NIR spectra.

  • 28.
    Nyström, Josefina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Stenberg, L
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ollmar, S
    Eriksson, J W
    Geladi, P
    Combined near-infrared spectroscopy and multifrequency bio-impedance investigation of skin alterations in diabetes patients based on multivariate analyses2003In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 41, no 3, p. 324-329Article in journal (Refereed)
    Abstract [en]

    A group of 34 diabetic men, with different degrees of diabetes complications, including skin changes, were studied by near-infrared (NIR) spectroscopy and total body multi-frequency bio-impedance analyses (MFBIA-body). Skin reflectance spectra were measured with a fibre-optic probe in four locations (sites): hand, arm, leg and foot. As control subjects, a group of 23 healthy males were also measured. A combined multivariate analysis of the two types of spectrum was performed. It was concluded that the NIR method has the potential to detect diabetes-related skin conditions and also that the combination of the two techniques provides a higher potential for classification and discrimination of the skin conditions, with correct classification increasing from 63% to 85%.

  • 29.
    Nyström, Josefina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Svensk, Ann-Christine
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Geladi, Paul
    Larson, Johan
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
    Franzén, Lars
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
    Comparison of three instrumental methods for the objective evaluation of radiotherapy induced erythema in breast cancer patients and a study of the effect of skin lotions2007In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 46, no 7, p. 893-899Article in journal (Refereed)
    Abstract [en]

    A non-blinded three armed study of the effect of Aloe vera, Essex and no lotion on erythema was performed. The erythema is an effect of radiotherapy treatment in breast cancer patients. The study required testing of objective methods for measuring the erythema. The chosen experimental methods were Near Infrared Spectroscopy, Laser Doppler Imaging and Digital Colour Photography. The experimental setup was made in such a way that in parallel with testing the effect of the lotions there was also a test of the sensitivity of the instruments. Fifty women were selected consecutively to participate in the study. They were all subjected to treatment with high-energy electrons (9-20 MeV) after mastectomy, 2Gy/day to a total dose of 50 Gy. Measurements were performed before the start of radiotherapy and thereafter once a week during the course of treatment. Aloe vera and Essex lotion were applied twice every radiation day in selected sites. The increase in skin redness could be monitored with all techniques with a detection limit of 8 Gy for Digital Colour Photography and Near Infrared Spectroscopy and 18 Gy for Laser Doppler Imaging. In clinical practice our recommendation is to use Digital Colour Photography. No significant median differences were observed between the pairs no lotion-Essex, no lotion-Aloe vera and Essex-Aloe vera for any of the techniques tested.

  • 30.
    Phal, Sereilakhena
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Geladi, Paul
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tesfalidet, Solomon
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Determination of methotrexate in spiked human blood serum using multi-frequency electrochemical immittance spectroscopy and multivariate data analysis2017In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 987, p. 15-24Article in journal (Refereed)
    Abstract [en]

    This article describes an attempt to develop a sensor based on multi-frequency immittance spectroscopy for the determination of methotrexate (MTX) in blood serum using gold electrodes modified with antibodies. The attachment of antibodies was monitored with electrochemical immittance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The EIS measurements of MTX resulted in a data matrix of size 39 × 55. The data were analysed using multivariate data analysis and showed a concentration dependence and time dependence that could be separated. This allowed the calculation of a multivariate calibration model. The model showed good linear behavior on a logarithmic scale offering a detection limit of 5 × 10−12 mol L−1.

  • 31.
    Phal, Sereilakhena
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shatri, Besart
    Berisha, Avni
    Geladi, Paul
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tesfalidet, Solomon
    Covalently electrografted carboxyphenyl layers onto gold surface serving as a platform for the construction of an immunosensor for detection of methotrexate2018In: Journal of Electroanalytical Chemistry, ISSN 1572-6657, Vol. 812, p. 235-243Article in journal (Refereed)
    Abstract [en]

    Abstract The classical way to modify a gold electrode surface for immunosensor development is through self-assembly of functionalised thiols for subsequent attachment of antibodies. Here is described a new pathway for surface modification using a diazonium salt-based immunosensor for detection of methotrexate (MTX) with electrochemical immittance spectroscopy (EIS). The diazonium salt, 4-carboxybenzenediazonium tetrafluoroborate was synthesized using a diazotization reaction and characterized by IR and cyclic voltammetry (CV). The Au electrode was electrografted with diazonium and used for anti-MTX antibody immobilization. The EIS detection of MTX was studied with and without application of redox probe; Fe(CN)63−/4−. MTX could not be detected using Fe(CN)63−/4−as redox probe, whereas EIS measurements without redox probe and analysis of the data with singular decomposition (SVD) gave good results. A multivariate calibration model showed good linear behavior on a logarithmic scale with a detection limit for MTX of 7×10−12molL−1.

  • 32. Ringstad, Lovisa
    et al.
    Protopapa, Elisabeth
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Schmidtchen, Artur
    Nelson, Andrew
    Malmsten, Martin
    An Electrochemical Study into the Interaction between Complement-Derived Peptides and DOPC Mono- and Bilayers2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 1, p. 208-216Article in journal (Refereed)
    Abstract [en]

    Electrochemical methods employing the hanging mercury drop electrode were used to study the interaction between variants of the complement-derived antimicrobial peptide CNY21 (CNYITELRRQH ARASHLGLAR) and dioleoyl phosphatidylcholine (DOPC) monolayers. Capacitance potential and impedance measurements showed that the CNY21 analogues investigated interact with DOPC monolayers coating the mercury drop. Increasing the peptide hydrophobicity by substituting the two histidine residues with leucine resulted in a deeper peptide penetration into the hydrophobic region of the DOPC monolayer, indicated by an increase in the dielectric constant of the lipid monolayer ( = 2.0 after 15 min interaction). Increasing the peptide net charge from +3 to +5 by replacing the histidines by lysines, on the other hand, arrests the peptide in the lipid head group region. Reduction of electroactive ions (Tl+, Pb2+, Cd2+, and Eu3+) at the monolayer-coated electrode was employed to further characterize the types of defects induced by the peptides. All peptides studied permeabilize the monolayer to Tl+ to an appreciable extent, but this effect is more pronounced for the more hydrophobic peptide (CNY21L), which also allows penetration of larger ions and ions of higher valency. The results for the various ions indicate that charge repulsion rather than ion size is the determining factor for cation penetration through peptide-induced defects in the DOPC monolayer. The effects obtained for monolayers were compared to results obtained with bilayers from liposome leakage and circular dichroism studies for unilamellar DOPC vesicles, and in situ ellipsometry for supported DOPC bilayers. Trends in peptide-induced liposome leakage were similar to peptide effects on electrochemical impedance and permeability of electroactive ions for the monolayer system, demonstrating that formation of transmembrane pores alone does not constitute the mechanism of action for the peptides investigated. Instead, our results point to the importance of local packing defects in the lipid membrane in close proximity to the adsorbed peptide molecules.

  • 33.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nyström, J.
    Geladi, P.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Electrolyte ion adsorption and charge blocking effect at the hematite/aqueous solution interface: an electrochemical impedance study using multivariate data analysis2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 17, p. 11560-11568Article in journal (Refereed)
    Abstract [en]

    A model-free multivariate analysis using singular value decomposition is employed to refine an equivalent electrical circuit model in order to probe the electrochemical properties of the hematite/water interface in dilute NaCl and NH4Cl solutions using electrochemical impedance spectroscopy. The result shows that the surface protonation is directly related to the mobility and trapping of charge carriers at the mineral surface. Moreover, the point of zero charge can be found at pH where the charge transfer resistance is the highest, in addition to the minimum double layer capacitance. The innersphere interaction of the NH4+ ion with the surface is indicated by an increase of capacitance for charge carrier trapping from the protonated surface as well as lower double layer capacitance and open circuit potential. It is clear that the intrinsic electrochemical activity of hematite depends on the degree of surface (de) protonation and other inner-sphere adsorption, as these processes affect the charge carrier density in the surface state. This work also highlights an important synergistic effect of the two spectral analyses that enables EIS to be utilized in an in-depth investigation of mineral/water interfaces.

  • 34.
    Tesfalidet, Solomon
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Geladi, Paul
    Shimizu, Kenichi
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lindholm-Sethson, Britta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Detection of methotrexate in a flow system using electrochemical impedance spectroscopy and multivariate data analysis2016In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 914, p. 1-6Article in journal (Refereed)
    Abstract [en]

    Abstract Methotrexate (MTX), a common pharmaceutical drug in cancer therapy and treatment of rheumatic diseases, is known to cause severe adverse side effects at high dose. As the side effect may be life threatening, there is an urgent need for a continuous, bed-side monitoring of the nominal MTX serum level in a patient while the chemical is being administered. This article describes a detection of MTX using a flow system that consists two modified gold electrodes. Interaction of MTX with the antibodies fixed on the electrode surface is detected by electrochemical impedance spectroscopy and evaluated using singular value decomposition (SVD). The key finding of this work is that the change in the electrode capacitance is found to be quantitative with respect to the concentration of MTX. Moreover a calibration curve constructed using the principal component regression method has a linear range of six orders of magnitude and a detection limit of 1.65 × 10−10 M.

1 - 34 of 34
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