| 1. |
- Andoralov, Viktor, et al.
(författare)
-
Flexible micro(bio)sensors for quantitative analysis of bioanalytes in a nanovolume of human lachrymal liquid
- 2013
-
Ingår i: Analytical and Bioanalytical Chemistry. - : Springer. - 1618-2642 .- 1618-2650. ; 405:11, s. 3871-3879
-
Tidskriftsartikel (refereegranskat)abstract
- A flexible electrochemical micro(bio)sensor has been designed for determination of several biological compounds, specifically, ascorbate, dopamine, and glucose, in human lachrymal liquid (tears). The microsensor for simultaneous determination of ascorbate and dopamine concentrations was based on a gold microwire modified with the tetrathiafulvalen–7,7,8,8-tetracyanoquinodimethane complex as a catalyst. To monitor glucose concentration in tears, glucose dehydrogenase was immobilized on a gold microwire modified with carbon nanotubes and an osmium redox polymer. A capillary microcell was constructed for sampling tears. The cell had a working volume of 60–100 nL with a sampling deviation of 6.7 %. To check if the microcell was properly filled with buffer or tear sample, a control electrode was introduced into the construction. The electrode was used to measure the electrical resistance of a fully filled nanovolume cell. The mechanical flexibility is one of the most important features of the prototype and allowed direct collection of tears with minimized risk of damage to the eye.
|
|
| 2. |
- Bahmanzadeh, Safiyeh, et al.
(författare)
-
Proteolytic degradation of gelatin-tannic acid multilayers
- 2018
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 526, s. 244-252
-
Tidskriftsartikel (refereegranskat)abstract
- Hypothesis Gelatin is one of the most popular constituents of biodegradable/edible films. Because of its poor mechanical properties, it typically needs to be cross-linked. In this regard, the use of tannic acid has attracted significant interest. Whereas the biodegradability of gelatin is well established, little is known on how different crosslinking methods affect biodegradability. In most cases, the ionic strength at which protein films are grown has a drastic effect on their structure. Thus, it is expected that by controlling the ionic strength during the growth of cross-linked gelatin films it should be possible to tune the access to relevant cleavage sites by proteases and, therefore, their biodegradability. Experiments Gelatin-tannic acid were grown at different ionic strengths by means of the layer-by-layer self-assembly method. The growth of these multilayers and their response to the presence of different proteases were monitored by means of Electrochemical Impedance Spectroscopy and Quartz Crystal Microbalance with Dissipation. Findings Gelatin-tannic acid multilayers grown at low ionic strength exhibited a swollen structure that allowed easy access to their cleavage sites by proteases. Multilayers formed at physiological ionic strength exhibited a compacter structure, which limited their proteolytic degradation.
|
|
| 3. |
- Bistolas, Nikitas, et al.
(författare)
-
Spectroelectrochemistry of cytochrome P450cam
- 2004
-
Ingår i: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 314:3, s. 810-816
-
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
|
|
| 4. |
- Björklund, Sebastian, et al.
(författare)
-
Skin membrane electrical impedance properties under the influence of a varying water gradient
- 2013
-
Ingår i: Biophysical Journal. - : Elsevier. - 0006-3495 .- 1542-0086. ; 104:12, s. 2639-2650
-
Tidskriftsartikel (refereegranskat)abstract
- The stratum corneum (SC) is an effective permeability barrier. One strategy to increase drug delivery across skin is to increase the hydration. A detailed description of how hydration affects skin permeability requires characterization of both macroscopic and molecular properties and how they respond to hydration. We explore this issue by performing impedance experiments on excised skin membranes in the frequency range 1 Hz to 0.2 MHz under the influence of a varying gradient in water activity (aw). Hydration/dehydration induces reversible changes of membrane resistance and effective capacitance. On average, the membrane resistance is 14 times lower and the effective capacitance is 1.5 times higher when the outermost SC membrane is exposed to hydrating conditions (aw ¼ 0.992), as compared to the case of more dehydrating conditions (aw ¼ 0.826). Molecular insight into the hydration effects on the SC components is provided by natural-abundance 13C polarization transfer solidstate NMR and x-ray diffraction under similar hydration conditions. Hydration has a significant effect on the dynamics of the keratin filament terminals and increases the interchain spacing of the filaments. The SC lipids are organized into lamellar structures with ~ 12.6 nm spacing and hexagonal hydrocarbon chain packing with mainly all-trans configuration of the acyl chains, irrespective of hydration state. Subtle changes in the dynamics of the lipids due to mobilization and incorporation of cholesterol and long-chain lipid species into the fluid lipid fraction is suggested to occur upon hydration, which can explain the changes of the impedance response. The results presented here provide information that is useful in explaining the effect of hydration on skin permeability.
|
|
| 5. |
- Björklund, Sebastian, et al.
(författare)
-
The effects of polar excipients transcutol and dexpanthenol on molecular mobility, permeability, and electrical impedance of the skin barrier
- 2016
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 479, s. 207-220
-
Tidskriftsartikel (refereegranskat)abstract
- In the development of transdermal and topical products it is important to understand how formulation ingredients interact with the molecular components of the upper layer of the skin, the stratum corneum (SC), and thereby influence its macroscopic barrier properties. The aim here was to investigate the effect of two commonly used excipients, transcutol and dexpanthenol, on the molecular as well as the macroscopic properties of the skin membrane. Polarization transfer solid-state NMR methods were combined with steady-state flux and impedance spectroscopy measurements to investigate how these common excipients influence the molecular components of SC and its barrier function at strictly controlled hydration conditions in vitro with excised porcine skin. The NMR results provide completely new molecular insight into how transcutol and dexpanthenol affect specific molecular segments of both SC lipids and proteins. The presence of transcutol or dexpanthenol in the formulation at fixed water activity results in increased effective skin permeability of the model drug metronidazole. Finally, impedance spectroscopy data show clear changes of the effective skin capacitance after treatment with transcutol or dexpanthenol. Based on the complementary data, we are able to draw direct links between effects on the molecular properties and on the macroscopic barrier function of the skin barrier under treatment with formulations containing transcutol or dexpanthenol.
|
|
| 6. |
- Cao, Zhen, et al.
(författare)
-
Enhancement of HFE-7200 pool boiling heat transfer on copper surfaces with nanoparticle coatings
- 2018
-
Ingår i: Proceeding: International Heat Transfer Conference 16. - 2377-424X. ; , s. 1341-1347
-
Konferensbidrag (refereegranskat)abstract
- Saturated pool boiling heat transfer of HFE-7200 is investigated experimentally on copper surfaces with nanoparticle coatings at atmospheric pressure. The coatings are generated by an electrophoretic deposition method. Two modified surfaces are prepared with Cu-Zinc nanoparticles of 0.3 mg and 0.6 mg, respectively. During the deposition, ethanol works as the solvent while the electrical potential and deposition time are controlled as 9.5 V and 30 min, respectively. The experimental results show heat transfer is considerably enhanced by the nanoparticle coatings. The surface with 0.6 mg nanoparticles (EDS-2) performs better than the surface with 0.3 mg nanoparticles (EDS-1), and a maximum 140% heat transfer enhancement is achieved on the surface EDS-2 compared with the SS. However, the critical heat flux is not enhanced by the coatings but even slightly decreased. A high speed visualization is employed to capture bubble behavior. It is found that bubbles on EDS-1 and EDS-2 have smaller sizes and higher departure frequency than those on the SS before reaching the critical heat flux. However, at critical heat fluxes, a vapor blanket appears on all surfaces.
|
|
| 7. |
- Cao, Zhen, et al.
(författare)
-
Enhancement of HFE-7200 pool boiling heat transfer on copper surfaces with nanoparticle coatings
- 2018
-
Ingår i: International Heat Transfer Conference 16. - Connecticut : Begell House. - 9781567004748 - 9781567004731 ; , s. -1347
-
Konferensbidrag (refereegranskat)abstract
- Saturated pool boiling heat transfer of HFE-7200 is investigated experimentally on copper surfaces with nanoparticle coatings at atmospheric pressure. The coatings are generated by an electrophoretic deposition method. Two modified surfaces are prepared with Cu-Zinc nanoparticles of 0.3 mg and 0.6 mg, respectively. During the deposition, ethanol works as the solvent while the electrical potential and deposition time are controlled as 9.5 V and 30 min, respectively. The experimental results show heat transfer is considerably enhanced by the nanoparticle coatings. The surface with 0.6 mg nanoparticles (EDS-2) performs better than the surface with 0.3 mg nanoparticles (EDS-1), and a maximum 140% heat transfer enhancement is achieved on the surface EDS-2 compared with the SS. However, the critical heat flux is not enhanced by the coatings but even slightly decreased. A high speed visualization is employed to capture bubble behavior. It is found that bubbles on EDS-1 and EDS-2 have smaller sizes and higher departure frequency than those on the SS before reaching the critical heat flux. However, at critical heat fluxes, a vapor blanket appears on all surfaces.
|
|
| 8. |
- Cao, Zhen, et al.
(författare)
-
Pool boiling heat transfer enhancement of water by gold nanoparticles with an electrophoretic deposition method
- 2019
-
Ingår i: Proceedings of the Asme International Mechanical Engineering Congress and Exposition, 2018, vol 8b. - : Amer Soc Mechanical Engineers. - 9780791852125
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Saturated pool boiling heat transfer of water is investigated experimentally on copper surfaces with nanoparticle coatings at atmospheric pressure. The coatings are generated by an electrophoretic deposition method (EPD). Three modified surfaces are prepared with gold nanoparticles of 0.20 mg, 0.25 mg and 0.30 mg, respectively. During the deposition, ethanol works as the solvent while the electrical potential and deposition time are controlled as 9.5 V and 30 min, respectively. The experimental results show that heat transfer coefficients (HTC) and critical heat fluxes (CHF) are enhanced on the modified surfaces. HTC increases with decreasing thickness of the coating, while CHF increases with increasing thickness of the coating. CHFs of EPD-0.20 mg, EPD-0.25 mg and EPD-0.30 mg are 93 W/cm2, 123 W/cm2 and 142 W/cm2, respectively, which are increased by 7%, 41% and 63% compared with the smooth surface. EPD-0.20 mg performs the best on heat transfer, with a maximum enhancement of around 60%. At the end, a brief review about mechanistic models of heat transfer at low and moderate heat fluxes is provided, based on which, the reasons why heat transfer is enhanced are discussed.
|
|
| 9. |
- Cao, Zhen, et al.
(författare)
-
Pool boiling of HFE-7200 on nanoparticle-coating surfaces: Experiments and heat transfer analysis
- 2018
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310 .- 1879-2189. ; 133, s. 548-560
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, an electrophoretic deposition method was employed to modify copper surfaces withCu-Zn (100 nm) nanoparticles. Pool boiling heat transfer of HFE-7200 on the modified surfaces was experimentally studied. The results showed that the heat transfer coefficient on the modified surfaces was significantly enhanced compared with that on a smooth surface, e.g., a maximum 100% enhancement,while the maximum superheat on the modified surfaces was around 20 K lower than that on the smooth surface. However, the critical heat flux (CHF) was not improved considerably, and supplementary tests indicated that the wickability of HFE-7200 was almost the same on the modified surfaces and the smooth surface. The departure diameters of bubbles were recorded by a high speed camera, which were compared with several models in literature. Active nucleation site sizes were evaluated by the Hsu nucleation theory and active nucleation site densities were estimated by appropriate correlations.In addition, a heat transfer model, considering natural convection, re-formation of thermal boundary layer and microlayer evaporation, was formulated to predict the heat transfer on the modified surfaces and the smooth surface. A relatively good prediction was achieved.
|
|
| 10. |
- Christenson, Andreas, et al.
(författare)
-
Direct electron transfer between ligninolytic redox enzymes and electrodes
- 2004
-
Ingår i: Electroanalysis. - : Wiley. - 1040-0397 .- 1521-4109. ; 16:13-14, s. 1074-1092
-
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.
|
|
