| 1. |
- Ahmad, Farook, et al.
(författare)
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Development of prototype wireless transmission measurement for glucose in subcutaneous and brain striatum
- 2008
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Ingår i: Electroanalysis. - : Wiley. - 1040-0397 .- 1521-4109. ; 20:9, s. 1008-1015
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Tidskriftsartikel (refereegranskat)abstract
- Monitoring of glucose in subcutaneous and brain striatum have been extensively studied in the past. While biocompatibility was one of the limitations, others included the messy measuring equipments preclude monitoring in a complex environment. This study tried to establish an amperometric measurement of glucose in pre- and post-insulin-administration on diabetic and hyperglycemia rats via wireless. The results have indicated that the wireless sensing kit used was capable of monitoring glucose in both subcutaneous and brain. The physiological data have also shown a new insight on the fabrication of implantable glucose sensors.
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| 2. |
- Ahmad, Farook, et al.
(författare)
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Minimizing tissue-material interaction in microsensor for subcutaneous glucose monitoring
- 2007
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Ingår i: Biosensors & Bioelectronics. - : Elsevier BV. - 1873-4235 .- 0956-5663. ; 22:8, s. 1625-1632
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Tidskriftsartikel (refereegranskat)abstract
- A new implantable electrocatalytic glucose sensor for subcutaneous glucose monitoring has been fabricated by immobilizing glucose oxidase on a chemically modified carbon fiber. The sensor was inserted subcutaneously on a male spraguely rat without any incision after dipping the microsensor in the rat's serum for 3 days. The so called "stained" microsensor, operated in the amperometric mode with an applied potential of +0.23 V versus Ag vertical bar AgCl, was able to directly measure the glucose concentration upon infusion of glucose. The results obtained were encouraging, with the response time was less than 2 s and the apparent Michaelis-Menten value at 5.1 +/- 0.5 mM. The "stained" microsensor shows good stability and reproducibility with constant response spanned over 25 days. Most common interferences in glucose analysis were minimized by the outerlayer Nafion((R)). Hematology examinations showed minimal material-tissue interaction. Use of such mechanical devices will allow a more refined understanding towards glucose control in diabetic patients as the implanted microsensor was not effected by biocompatibility failures. (c) 2006 Elsevier B.V. All rights reserved.
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| 3. |
- Bistolas, Nikitas, et al.
(författare)
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Spectroelectrochemistry of cytochrome P450cam
- 2004
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Ingår i: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 314:3, s. 810-816
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Tidskriftsartikel (refereegranskat)abstract
- The spectroelectrochemistry of camphor-bound cytochrome P450cam (P450cam) using gold electrodes is described. The electrodes were modified with either 4,4′-dithiodipyridin or sodium dithionite. Electrolysis of P450cam was carried out when the enzyme was in solution, while at the same time UV–visible absorption spectra were recorded. Reversible oxidation and reduction could be observed with both 4,4′-dithiodipyridin and dithionite modified electrodes. A formal potential (E0′) of −373 mV vs Ag/AgCl 1 M KCl was determined. The spectra of P450cam complexed with either carbon monoxide or metyrapone, both being inhibitors of P450 catalysis, clearly indicated that the protein retained its native state in the electrochemical cell during electrolysis
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| 4. |
- Christenson, Andreas, et al.
(författare)
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Direct and mediated electron transfer between intact succinate:quinone oxidoreductase from Bacillus subtilis and a surface modified gold electrode reveals redox state-dependent conformational changes.
- 2008
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728. ; 1777:9, s. 1203-1210
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Tidskriftsartikel (refereegranskat)abstract
- Succinate:quinone oxidoreductase (SQR) from Bacillus subtilis consists of two hydrophilic protein subunits comprising succinate dehydrogenase, and a di-heme membrane anchor protein harboring two putative quinone binding sites, Q(p) and Q(d). In this work we have used spectroelectrochemistry to study the electronic communication between purified SQR and a surface modified gold capillary electrode. In the presence of two soluble quinone mediators the midpoint potentials of both hemes were revealed essentially as previously determined by conventional redox titration (heme b(H), E(m)=+65 mV, heme b(L), E(m)=-95 mV). In the absence of mediators the enzyme still communicated with the electrode, albeit with a reproducible hysteresis, resulting in the reduction of both hemes occurring approximately at the midpoint potential of heme b(L), and with a pronounced delay of reoxidation. When the specific inhibitor 2-n-heptyl-4 hydroxyquinoline N-oxide (HQNO), which binds to Q(d) in B. subtilis SQR, was added together with the two quinone mediators, rapid reductive titration was still possible which can be envisioned as an electron transfer occurring via the HQNO insensitive Q(p) site. In contrast, the subsequent oxidative titration was severely hampered in the presence of HQNO, in fact it completely resembled the unmediated reaction. If mediators communicate with Q(p) or Q(d), either event is followed by very rapid electron redistribution within the enzyme. Taken together, this strongly suggests that the accessibility of Q(p) depended on the redox state of the hemes. When both hemes were reduced, and Q(d) was blocked by HQNO, quinone-mediated communication via the Q(p) site was no longer possible, revealing a redox-dependent conformational change in the membrane anchor domain.
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| 5. |
- Christenson, Andreas, et al.
(författare)
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Direct electron transfer between ligninolytic redox enzymes and electrodes
- 2004
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Ingår i: Electroanalysis. - : Wiley. - 1040-0397 .- 1521-4109. ; 16:13-14, s. 1074-1092
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Forskningsöversikt (refereegranskat)abstract
- The electrochemistry of the ligninolytic redox enzymes, which include lignin peroxidase, manganese peroxidase and laccase and possibly also cellobiose dehydrogenase, is reviewed and discussed in conjunction with their basic biochemical characteristics. It is shown that long-range electron transfer between these enzymes and electrodes can be established and their ability to degrade lignin through a direct electron transfer mechanism is discussed.
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| 6. |
- Christenson, Andreas, et al.
(författare)
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Direct heterogeneous electron transfer of theophylline oxidase
- 2004
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Ingår i: Biosensors & Bioelectronics. - : Elsevier BV. - 1873-4235 .- 0956-5663. ; 20:2, s. 176-183
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Tidskriftsartikel (refereegranskat)abstract
- Direct electron transfer (DET) was shown between the heme containing enzyme theophylline oxidase (ThO) and the surface of both graphite and gold electrodes. As proof on graphite a steady state current for theophylline was recorded using the electrode modified with adsorbed ThO. The electrode showed a Michaelis–Menten-like response to theophylline with a detection limit of 0.2 mM and a Michaelis–Menten constant equal to 3.2 mM. These initial results open up a possibility for the development of reagentless third generation biosensor based on heterogeneous DET between ThO and an electrode. On gold DET between ThO and the surface of aldrithiol modified gold was studied with spectroelectrochemical measurements. DET was observed for soluble ThO as a change of its spectrum in a gold capillary responding to a change in the applied potential. It was shown that the redox conversion of the heme domain of the enzyme is directly (mediatorlessly) driven by the potential applied at the gold electrode. The measurements enabled an estimation of the formal potential (E°′) of the redox process equal to −275±50 mV versus Ag|AgClsat at pH 7.0. The experimentally determined number of the electrons involved in this heterogeneous electron transfer process was estimated to be equal to 0.53. The low precision in determination of the E°′ and the value of the number of electrons lower than one indicate that kinetic restrictions disturbed the evaluation of the true thermodynamic values from relatively fast spectroelectrochemical measurements. . . . This is the final, accepted and revised manuscript of this article. Use alternative location to go to the published article. Requires subscription.
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| 7. |
- Christenson, Andreas, et al.
(författare)
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Redox potentials of the blue copper sites of bilirubin oxidases
- 2006
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728. ; 1757:12, s. 1634-1641
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Tidskriftsartikel (refereegranskat)abstract
- The redox potentials of the multicopper redox enzyme bilirubin oxidase (BOD) from two organisms were determined by mediated and direct spectroelectrochemistry. The potential of the T1 site of BOD from the fungus Myrothecium verrucaria was close to 670 mV, whereas that from Trachyderma tsunodae was > 650 mV vs. NHE. For the first time, direct electron transfer was observed between gold electrodes and BODs. The redox potentials of the T2 sites of both BODs were near 390 mV vs. NHE, consistent with previous finding for laccase and suggesting that the redox potentials of the T2 copper sites of most blue multicopper oxidases are similar, about 400 mV (c) 2006 Elsevier B.V. All rights reserved.
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| 8. |
- Christenson, Andreas
(författare)
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Spectroelectrochemistry of Redox Enzymes
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A low volume and long optical path spectroelectrochemical cell was constructed and tested in a number of applications such as detection of direct electron transfer (DET) between redox enzymes and gold electrodes, determination of the formal potentials of redox centres in proteins and enzymes, as well as mechanistic studies of heterogeneous and intermolecular electron transfer of copper oxidases and succinate:quinine oxidoreductase (Complex II). The existence of DET between enzymes and electrodes was demonstrated for theophylline oxidase, cytochrome P450 cam, laccase, bilirubin oxidase, sulphite oxidase and Complex II. Spectroelectrochemical investigations of the ET between blue multi-copper oxidases and gold electrodes demonstrated that the mechanism of heterogeneous ET of laccases on gold is completely different from that usually observed on carbon electrodes. At carbon electrodes laccases are electronically connected to the conducting electrode through the T1 copper centre. At gold surfaces, by contrast, the electronic connection of the laccase redox centre to the surface is established through the T2 copper centre. Such an ET connection between the gold surface and the T2 copper centre, severely disturbs the oxygen reduction reaction catalysed by laccase. Similar observation was made for two bilirubin oxidases. Spectroelectrochemical studies of Complex II in the gold capillary cell showed that DET for intact Complex II is realised through the heme center with a low redox potential, hemeL. The study of DET reactions in combination with specific ET mediators and inhibitors, suggested that a postulated proximal quinone binding site may indeed exist in the Complex II structure. Our spectroelectrochemical studies indicate that this quinone binding site seems to be closed when both high and low potential heme sites are reduced.
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| 9. |
- Christenson, Nina, 1975-, et al.
(författare)
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Riskville – A game for learning about disaster risks and urban planning
- 2018
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Ingår i: International Journal of Mass Emergencies and Disasters. - Colorado Springs, CO : International Research Committee on Sociology of Disasters; International Sociological Association. - 0280-7270. ; 36:3, s. 238-246
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Tidskriftsartikel (refereegranskat)abstract
- Education plays a key role in disaster risk reduction (DRR) and in creating resilient societies worldwide by disseminating information about risks and in improving people’s risk awareness. This, in turn, helps them to prepare, cope with and recover from possible disaster events, hence making the societies more resilient. This paper shortly presents the theoretical background and the rules of the game Riskville where the participants get to experience in a hands-on manner the connections and conflicts between urban planning, different interests and climate related risks. We conclude that Riskville promotes discussions on different perspectives on disaster risk and resilience and approaches in including them into urban planning.
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| 10. |
- Dock, Eva, et al.
(författare)
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A steady-state and flow-through cell for screen-printed eight-electrode arrays
- 2005
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Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 1873-4324 .- 0003-2670. ; 531:2, s. 165-172
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Tidskriftsartikel (refereegranskat)abstract
- An electrochemical cell has been developed enabling amperometric steady-state- and flow-injection measurements with screen-printed arrays consisting of eight working electrodes (circle divide = 1 mm) arranged radially around a printed Ag/AgCl reference electrode in the centre. The cell contained a rotator, providing similar hydrodynamics over all the working electrodes in the array, which was manually centered under the rotator. The reproducibility of steady-state measurements with eight-electrode platinum or gold arrays in this cell was studied by measuring and comparing currents from ferricyanide reduction at each electrode in the array. It was found that the relative standard deviation (R.S.D.) for the currents at different electrodes on one array was below 5%. Similar R.S.D. was found if measurements were compared between several arrays. This indicates that manual insertion/positioning of the eight-electrode array in the cell and hydrodynamics at the electrodes provided measurement reproducibility similar to the reproducibility of manufacturing eight-electrode platinum or gold arrays by screen-printing. A comparative study was performed between screen-printed and through mask sprayed carbon arrays. It was found that the reproducibility of the sprayed arrays was similar to that of the platinum or gold screen-printed arrays, with R.S.D. values below 6% regarding the variation between electrodes within the same array and the variation between different arrays. To enable flow-injection measurements, a tube (0.4 mm inner diameter) was inserted into a hole drilled through the centre of the steady-state cell rotator. This construction made it possible to inject the solution into the cell through the tube (not rotating), while the rotator was spinning over the eight-electrode array. It was found that this combination of flow-injection and mixing by a rotator provided a uniform current response over the array electrodes and that, at optimum conditions, the R.S.D. values between the eight electrodes in the array were nearly the same as in case of the steady-state measurements, i.e., below 5%. (C) 2004 Elsevier B.V. All rights reserved.
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