| 1. |
- Glasbey, JC, et al.
(author)
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- 2021
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swepub:Mat__t
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| 2. |
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| 3. |
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| 4. |
- Torne, Pablo, et al.
(author)
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A Search for Pulsars around Sgr A* in the First Event Horizon Telescope Data Set
- 2023
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In: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 959:1
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Journal article (peer-reviewed)abstract
- In 2017 the Event Horizon Telescope (EHT) observed the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), at a frequency of 228.1 GHz (lambda = 1.3 mm). The fundamental physics tests that even a single pulsar orbiting Sgr A* would enable motivate searching for pulsars in EHT data sets. The high observing frequency means that pulsars-which typically exhibit steep emission spectra-are expected to be very faint. However, it also negates pulse scattering, an effect that could hinder pulsar detections in the Galactic center. Additionally, magnetars or a secondary inverse Compton emission could be stronger at millimeter wavelengths than at lower frequencies. We present a search for pulsars close to Sgr A* using the data from the three most sensitive stations in the EHT 2017 campaign: the Atacama Large Millimeter/submillimeter Array, the Large Millimeter Telescope, and the IRAM 30 m Telescope. We apply three detection methods based on Fourier-domain analysis, the fast folding algorithm, and single-pulse searches targeting both pulsars and burst-like transient emission. We use the simultaneity of the observations to confirm potential candidates. No new pulsars or significant bursts were found. Being the first pulsar search ever carried out at such high radio frequencies, we detail our analysis methods and give a detailed estimation of the sensitivity of the search. We conclude that the EHT 2017 observations are only sensitive to a small fraction (less than or similar to 2.2%) of the pulsars that may exist close to Sgr A*, motivating further searches for fainter pulsars in the region.
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| 5. |
- Bobrowski, Tim, et al.
(author)
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Rechargeable, flexible and mediator-free biosupercapacitor based on transparent ITO nanoparticle modified electrodes acting in mu M glucose containing buffers
- 2018
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In: Biosensors & bioelectronics. - : Elsevier. - 0956-5663 .- 1873-4235. ; 101, s. 84-89
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Journal article (peer-reviewed)abstract
- We present a transparent and flexible self-charging biosupercapacitor based on an optimised mediator- and membrane-free enzymatic glucose/oxygen biofuel cell. Indium tin oxide (ITO) nanoparticles were spray-coated on transparent conducting ITO supports resulting in a flocculent, porous and nanostructured electrode surface. By this, high capacitive currents caused by an increased electrochemical double layer as well as enhanced catalytic currents due to a higher number of immobilised enzyme molecules were obtained. After a chemical pretreatment with a silane derivative, bilirubin oxidase from Myrothecium verrucaria was immobilized onto the ITO nanostructured electrode surface under formation of a biocathode, while bioanodes were obtained by either immobilisation of cellobiose dehydrogenase from Corynascus thermophilus or soluble PQQ-dependent glucose dehydrogenase from Acinetobacter calcoaceticus. The latter showed a lower apparent K-M value for glucose conversion and higher catalytic currents at mu M glucose concentrations. Applying the optimised device as a biosupercapacitor in a discontinuous charge/discharge mode led to a generated power output of 0.030 mW/cm(2) at 50 mu M glucose, simulating the glucose concentration in human tears. This represents an enhancement by a factor of 350 compared to the power density obtained from the continuously operating biofuel cell with a maximum power output of 0.086 mu W/cm(2) under the same conditions. After 17 h of charging/discharging cycles a remarkable current enhancement was still measured. The entire device was transferred to flexible materials and applied for powering a flexible display showing its potential applicability as an intermittent power source in smart contact lenses.
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| 6. |
- Gonzalez-Arribas, Elena, et al.
(author)
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Transparent, mediator- and membrane-free enzymatic fuel cell based on nanostructured chemically modified indium tin oxide electrodes
- 2017
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In: Biosensors & bioelectronics. - : Elsevier. - 0956-5663 .- 1873-4235. ; 97, s. 46-52
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Journal article (peer-reviewed)abstract
- We detail a mediator- and membrane-free enzymatic glucose/oxygen biofuel cell based on transparent and nanostructured conducting supports. Chemically modified indium tin oxide nanoparticle modified electrodes were used to substantially increase the active surface area without significantly compromising transparency. Two different procedures for surface nanostructuring were employed, viz. spray-coating and drop-coating. The spray-coated biodevice showed superior characteristics as compared to the drop-coated enzymatic fuel cell, as a result of the higher nanostructured surface area as confirmed by electrochemical characterisation, as well as scanning electron and atomic force microscopy. Subsequent chemical modification with silanes, followed by the immobilisation of either cellobiose dehydrogenase from Corynascus thermophiles or bilirubin oxidase from Myrothecium verrucaria, were performed to obtain the bioanodes and biocathodes, respectively. The optimised biodevice exhibited an OCV of 0.67 V and power output of up to 1.4 mu W/cm(2) at an operating voltage of 0.35 V. This is considered a significant step forward in the field of glucose/oxygen membrane- and mediator-free, transparent enzymatic fuel cells.
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| 7. |
- Ortiz, Roberto, et al.
(author)
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Engineering of Cellobiose Dehydrogenases for Improved Glucose Sensitivity and Reduced Maltose Affinityydrogenases for Improved Glucose Sensitivity and Reduced Maltose Affinity
- 2017
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In: ChemElectroChem. - : Wiley. - 2196-0216. ; 4:4, s. 846-855
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Journal article (peer-reviewed)abstract
- Cellobiose dehydrogenase (CDH) is a fungal extracellular flavocytochrome capable of direct electron transfer (DET). Unlike other CDHs, the pH optimum for CDHs from Corynascus thermophilus (CtCDH) and Humicola insolens (HiCDH) is close to the human physiological pH in blood (7.4). These are, therefore, interesting candidates for glucose measurements in human blood and the application in enzymatic fuel cells is, however, limited by their relatively low activity with this substrate. In this work, the substrate specificities of CtCDH and HiCDH have been altered by a single cysteine to tyrosine substitution in the active sites of CtCDH (position 291) and HiCDH (position 285), which resulted in improved kinetic constants with glucose while decreasing the activity with several disaccharides, including maltose. The DET properties of the generated CDH variants were tested in the absence and in the presence of substrates, on graphite electrodes and thiolic self-assembled monolayer (SAM)-modified Au electrodes. Seven different thiols with different spacer lengths were used, containing -COOH, -OH, and -NH2 end groups. The length and head functionality of the thiol govern the efficiency of the DET reaction and indicate different DET properties of CtCDH and HiCDH
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| 8. |
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| 9. |
- Schulz, Christopher, et al.
(author)
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Enhancement of enzymatic activity and catalytic current of cellobiose dehydrogenase by calcium ions
- 2012
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In: Electrochemistry Communications. - : Elsevier BV. - 1388-2481. ; 17, s. 71-74
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Journal article (peer-reviewed)abstract
- Cellobiose dehydrogenase (CDH) has recently become a redox enzyme at focus in bioelectrochemistry especially for the construction of sugar biosensors and biofuel cell anodes. The present study shows that an increase in the CaCl2 concentration to up to 100 mM led to an increase in the maximal catalytic current generated by two different Ascomycete and one Basidiomycete CDH immobilised on a spectroscopic graphite electrode. For the Ascomycete Myriococcum therrnophilum CDH the catalytic current was increased 5.1 fold, whereas Ascomycete Humicola insolens CDH showed a four-fold increase and Basidiomycete Phanerochaete chrysosporium CDH showed an increase by a factor of 2.4. On the other hand, the addition of a monovalent cation salt, KCl (up to 100 mM), to the buffers increased the catalytic currents only up to 2-fold for Myriococcum thermophilum CDH. Activity assays in solution with cyt c accepting solely the electrons from the CYTCDH domain also revealed an increased activity in the presence of CaCl2. Experiments with the isolated DHCDH domain from Humicola insolens have shown that the catalytic turnover is totally independent on the addition of KCl or CaCl2 to the solution. The results indicate a positive effect of metal cations, particularly Ca2+, on the electron transfer between the DHCDH and the CYTCDH domains or between the CYTCDH domain and the final electron acceptor, whereas the first hypothesis is favoured. These findings are of interest both for the construction of 3 rd generation biosensors and biofuel cell anodes, and also for a deeper understanding of the electron transfer mechanism in CDH. (C) 2012 Elsevier B.V. All rights reserved.
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| 10. |
- Shao, Minling, et al.
(author)
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Optimization of a Membraneless Glucose/Oxygen Enzymatic Fuel Cell Based on a Bioanode with High Coulombic Efficiency and Current Density
- 2013
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In: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 14:10, s. 2260-2269
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Journal article (peer-reviewed)abstract
- After initial testing and optimization of anode biocatalysts, a membraneless glucose/oxygen enzymatic biofuel cell possessing high coulombic efficiency and power output was fabricated and characterized. Agaricus meleagris (AmPDH) and flavodehydrogenase domains of various cellobiose dehydrogenases (DHCDH) were tested during the pre-screening. Myrothecium verrucaria adsorbed on graphite. Optimization showed that the current density for the mixed enzyme electrode could be further improved by using a genetically engineered variant of the non-glycosylated flavodehydrogenase domain of cellobiose dehydrogenase from Corynascus thermophilus expressed in E. coli (ngDH(CtCDHC310Y)) with a high glucose-turnover rate in combination with an Os-complex-modified redox polymer with a high concentration of Os complexes as well as a low-density graphite electrode. AmPDH/ngDH(CtCDHC310Y) anode showed not only a similar maximum voltage as with the biofuel cell based only on the ngDH(CtCDHC310Y) anode (0.55 V) but also a substantially improved maximum power output (20 Wcm(-2)) at 300 mV cell voltage in air-saturated physiological buffer. Most importantly, the estimated half-life of the mixed biofuel cell can reach up to 12 h, which is apparently longer than that of a biofuel cell in which the bioanode is based on only one single enzyme.
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