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University of Twente Publications (52,047 recursos)
University of Twente Repository provides publications of UT scientific staff, in many cases full text and publicly available.

Group = KEUR

Mostrando recursos 1 - 20 de 6,960

1. Apate: anti-phishing analysing and triaging environment (Poster) - Lastdrager, Elmer; Hartel, Pieter; Junger, Marianne

2. A novel side electrode configuration integrated in fused silica microsystems for synchronous optical and electrical spectroscopy - Sukas, S.; Schreuder, E.; Wagenaar, B. de; Swennenhuis, J.; Berg, A. van den; Terstappen, L.; Le Gac, S.
We present a novel electrode configuration consisting of coplanar side electrode pairs integrated at the half height of the microchannels for the creation of a homogeneous electric field distribution as well as for synchronous optical and electrical measurements. For the integration of such electrodes in fused silica microsystems, a dedicated microfabrication method was utilized, whereby an intermediate bonding layer was applied to lower the temperature for fusion bonding to avoid thereby metal degradation and subsequently to preserve the electrode structures. Finally, we demonstrate the applicability of our devices with integrated electrodes for single cell electrical lysis and simultaneous fluorescence and...

3. Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer - Visser, Claas Willem; Pohl, Ralph; Sun, Chao; Römer, Gert-Willem; Huis in 't Veld, Bert; Lohse, Detlef
3D printing of common metals is highly challenging because metals are generally solid at room conditions. Copper and gold pillars are manufactured with a resolution below 5 μm and a height up to 2 mm, using laser-induced forward transfer to create and eject liquid metal droplets. The solidified drop's shape is crucial for 3D printing and is discussed as a function of the laser energy

4. Ejection Regimes in Picosecond Laser-Induced Forward Transfer of Metals - Pohl, Ralph; Visser, Claas Willem; Römer, Gert-Willem; Lohse, Detlef; Sun, Chao; Huis in 't Veld, Bert
Laser-induced forward transfer (LIFT) is a 3D direct-write method suitable for precision printing of various materials, including pure metals. To understand the ejection mechanism and thereby improve deposition, here we present visualizations of ejection events at high-spatial (submicrometer) and high-temporal resolutions, for picosecond LIFT of copper and gold films with a thickness 50  nm≤d≤400  nm . For increasing fluences, these visualizations reveals the fluence threshold below which no ejection is observed, followed by the release of a metal cap (i.e., a hemisphere-shaped droplet), the formation of an elongated jet, and the release of a metal spray. For each ejection regime, the driving...

5. Sensitivity and detection limit analysis of silicon nanowire bio(chemical) sensors - Chen, Songyue; Berg, Albert van den; Carlen, Edwin T.
This paper presents an analysis of the sensitivity and detection limit of silicon nanowire biosensors using an analytical model in combination with I-V and current noise measurements. The analysis shows that the limit of detection (LOD) and signal to noise ratio (SNR) can be optimized by determining an operating point in the depletion region with a large sensor transconductance, while maintaining a small system output noise amplitude. Both sensor and measurement configurations play equally important roles for optimal sensor performance. The analysis also shows that the LOD and SNR are minimally affected by the sensor cross-sectional geometry and size

6. Plasmon-modulated photoluminescence from gold nanostructures and its dependence on plasmon resonance, excitation energy, and band structure - Le Thi Ngoc, Loan; Wiedemair, Justyna; Berg, Albert van den; Carlen, Edwin T.
Two distinct single-photon plasmon-modulated photoluminescence processes are generated from nanostructured gold surfaces by tuning the spectral overlap of the incident laser source, localized surface plasmon resonance band, and the interband transitions between the d and sp bands, near the X-and L-symmetry points of the electronic band structure of gold. In the main section of the article, the characteristics of these photoluminescence processes are described and discussed. In the last section, the background continuum accompanying surface-enhanced Raman scattering (SERS) spectra from benzenethiol and 4-mercaptopyridine self-assembled monolayers chemisorbed on nanostructured gold surfaces is shown to originate from plasmon-modulated photoluminescence.

7. Measuring direct current trans-epithelial electrical resistance in organ-on-a-chip microsystems - Odijk, Mathieu; Meer, Andries D. van der; Levner, Daniel; Kim, Hyun Jung; Helm, Marinke W. van der; Segerink, Loes I.; Frimat, Jean-Philippe; Hamilton, Geraldine A.; Ingber, Donald E.; Berg, Albert van den
Trans-epithelial electrical resistance (TEER) measurements are widely used as real-time, non-destructive, and label-free measurements of epithelial and endothelial barrier function. TEER measurements are ideal for characterizing tissue barrier function in organs-on-chip studies for drug testing and investigation of human disease models; however, published reports using this technique have reported highly conflicting results even with identical cell lines and experimental setups. The differences are even more dramatic when comparing measurements in conventional Transwell systems with those obtained in microfluidic systems. Our goal in this work was therefore to enhance the fidelity of TEER measurements in microfluidic organs-on-chips, specifically using direct current...

8. Mechanisms for leveraging models at runtime in self-adaptive software - Bennaceur, Amel; France, Robert; Tamburelli, Giordano; Vogel, Thomas; Mosterman, Pieter J.; Cazzola, Walter; Costa, Fabio M.; Pierantonio, Alfonso; Tichy, Matthias; Aksit, Mehmet; Emanuelson, Pär; Gang, Huang; Georgantas, Nikolaos; Redlich, David
Modern software systems are often required to adapt their behavior at runtime in order to maintain or enhance their utility in dynamic environments. Models at runtime research aims to provide suitable abstractions, techniques, and tools to manage the complexity of adapting software systems at runtime. In this chapter, we discuss challenges associated with developing mechanisms that leverage models at runtime to support runtime software adaptation. Specifically, we discuss challenges associated with developing effective mechanisms for supervising running systems, reasoning about and planning adaptations, maintaining consistency among multiple runtime models, and maintaining fidelity of runtime models with respect to the running...

9. Online monitoring of biofouling using coaxial stub resonator technique - Hoog, N.A.; Mayer, M.J.J.; Miedema, H.; Olthuis, W.; Tomaszweska, A.A.; Paulitsch-Fuchs, A.H.; Berg, A. van den
Here we demonstrate the proof-of-principle that a coaxial stub resonator can be used to detect early stages of biofilm formation. After promising field tests using a stub resonator with a stainless steel inner conductor as sensitive element, the sensitivity of the system was improved by using a resonator of shorter physical length, implying higher resonance frequencies (and by that a higher frequency range of operation) and improved sensitivity towards dispersion. In addition, the space between inner and outer conductor was filled up with glass beads, thereby exploiting the larger surface area available for biofilm formation. Analysis of the biofilm and the...

10. Functionalization and bioimmobilization of silicon surfaces with Si-N bonded monolayer - Masood, Muhammad Nasir; Carlen, Edwin T.; Berg, Albert van den
A new method for selective surface functionalization of silicon with a silicon-nitrogen bonded (Si-N) monolayer and subsequent bioimmobilization is presented. The Si-N monolayer was studied using Xray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), fluorescence spectroscopy, and capacitance-voltage (C-V) measurements using an electrolyte insulator semiconductor (EIS) sensor. A symmetric ethylene diamine (EDA, C2H4 (NH2)(2)) molecule was used as a precursor compound for monolayer formation in an inert environment in the liquid phase. XPS results show the attachment of EDA molecules proceeds via dissociative and dative bond formation whereas free amine groups on the surface were used for further immobilization of...

11. Capacitive deionization on-chip as a method for microfluidic sample preparation - Roelofs, Susan H.; Kim, Bumjoo; Eijkel, Jan C.T.; Han, Jongyoon; Berg, Albert van den; Odijk, Mathieu
Desalination as a sample preparation step is essential for noise reduction and reproducibility of mass spectrometry measurements. A specific example is the analysis of proteins for medical research and clinical applications. Salts and buffers that are present in samples need to be removed before analysis to improve the signal-to-noise ratio. Capacitive deionization is an electrostatic desalination (CDI) technique which uses two porous electrodes facing each other to remove ions from a solution. Upon the application of a potential of 0.5 V ions migrate to the electrodes and are stored in the electrical double layer. In this article we demonstrate CDI...

12. Microfluidic single sperm entrapment and analysis - Wagenaar, B. de; Berendsen, J.T.W.; Bomer, J.G.; Olthuis, W.; Berg, A. van den; Segerink, L.I.
Selection of healthy spermatozoa is of crucial importance for the success rates of assisted reproduction technologies (ART) such as in vitro fertilization and intra-cytoplasmic sperm injection. Although sperm selection for ART procedures is predominantly based on sperm motility, successful fertilization is not predicted by good motility alone. For example, sperm characteristics such as the acrosome state and DNA integrity have shown significant impact on ART outcome. Although fertilization can be achieved with a single spermatozoon of high quality, current quality assessments are population-based and do not allow investigation of multiple sperm characteristics on a single spermatozoon simultaneously. In order to...

13. Large scale patterning of hydrogel microarrays using capillary pinning - Gumuscu, Burcu; Bomer, Johan G.; Berg, Albert van den; Eijkel, Jan C.T.
Capillary barriers provide a simple and elegant means for autonomous fluid-flow control in microfluidic systems. In this work, we report on the fabrication of periodic hydrogel microarrays in closed microfluidic systems using non-fluorescent capillary barriers. This design strategy enables the fabrication of picoliter-volume patterns of photopolymerized and thermo-gelling hydrogels without any defects and distortions.

14. Imaging of the Ejection Process of Nanosecond Laser-induced forward Transfer of Gold - Pohl, R.; Visser, C.W.; Römer, G.R.B.E.; Sun, C.; Huis in 't Veld, A.J.; Lohse, D.
Laser-induced forward transfer is a direct-write process suitable for high precision 3D printing of several materials. However, the driving forces related to the ejection mechanism of the donor ma-terial are still under debate. To gain further insights into the ejection dynamics, this article presents results of a series of imaging experiments of the release process of nanosecond LIFT of a 200 nm thick gold donor layer. Images were obtained using a setup which consists of two dual-shutter cam-eras. Both cameras were combined with a 50× long-distance microscope and used to capture coaxial and side-view images of the ejection process. Bright...

15. In situ surface-enhanced raman spectroelectrochemical analysis system with a hemin modified nanostructured gold surface - Yuan, Tao; Le Thi Ngoc, Loan; Nieuwkasteele, Jan van; Odijk, Mathieu; Berg, Albert van den; Permentier, Hjalmar; Bischoff, Rainer; Carlen, Edwin T.
An integrated surface-enhanced Raman scattering (SERS) spectroelectrochemical (SEC) analysis system is presented that combines a small volume microfluidic sample chamber (<100 mu L) with a compact three-electrode configuration for in situ surface-enhanced Raman spectroelectrochemistry. The SEC system includes a nanostructured Au surface that serves dual roles as the electrochemical working electrode (WE) and SERS substrate, a microfabricated Pt counter electrode (CE), and an external Ag/AgCl reference electrode (RE). The nanostructured Au WE enables highly sensitive in situ SERS spectroscopy through large and reproducible SERS enhancements, which eliminates the need for resonant wavelength matching of the laser excitation source with the...

16. Improving chip-to-chip precision in disposable microchip capillary electrophoresis devices with internal standards - Bidulock, Allison C.E.; Berg, Albert van den; Eijkel, Jan C.T.
To realize portable systems for routine measurements in point-of-care settings, MCE methods are required to be robust across many single-use chips. While it is well-known internal standards (ISTDs) improve run-to-run precision, a systematic investigation is necessary to determine the significance of chip-to-chip imprecision in MCE and how ISTDs account for it. This paper addresses this question by exploring the reproducibility of Na quantification across six basic, in-house fabricated microchips. A dataset of 900 electrophoerograms was collected from analyzing five concentrations of NaCl with two ISTDs (CsCl and LiCl). While both improved the peak area reproducibility, the Na/Cs ratio was superior...

17. A versatile electrophoresis-based self-test platform - Staal, Steven; Ungerer, Mathijn; Floris, Arjan; Brinke, Hans-Willem ten; Helmhout, Roy; Tellegen, Marian; Janssen, Kjeld; Karstens, Erik; Arragon, Charlotte van; Lenk, Stefan; Staijen, Erik; Bartholomew, Jody; Krabbe, Hans; Movig, Kris; Dubsky, Pavel; Berg, Albert van den; Eijkel, Jan
This paper reports on recent research creating a family of electrophoresis-based point of care devices for the determination of a wide range of ionic analytes in various sample matrices. These devices are based on a first version for the point-of-care measurement of Li+, reported in 2010 by Floris etal. (Lab Chip 2010, 10, 1799-1806). With respect to this device, significant improvements in accuracy, precision, detection limit, and reliability have been obtained especially by the use of multiple injections of one sample on a single chip and integrated data analysis. Internal and external validation by clinical laboratories for the determination of...

18. Mass spectrometric detection of short-lived drug metabolites generated in an electrochemical microfluidic chip - Brink, Floris T.G. van den; Büter, Lars; Odijk, Mathieu; Olthuis, Wouter; Karst, Uwe; Berg, Albert van den
The costs of drug development have been rising exponentially over the last six decades, making it essential to select drug candidates in the early drug discovery phases before proceeding to expensive clinical trials. Here, we present novel screening methods using an electrochemical chip coupled online to mass spectrometry (MS) or liquid chromatography (LC) and MS, to generate phase I and phase II drug metabolites and to demonstrate protein modification by reactive metabolites. The short transit time (similar to 4.5 s) between electrochemical oxidation and mass spectrometric detection, enabled by an integrated electrospray emitter, allows us to detect a short-lived radical...

19. Innovations in STEM education: the Go-Lab federation of online labs - Jong, Ton de; Sotiriou, Sofoklis; Gillet, Dennis
The Go-Lab federation of online labs opens up virtual laboratories (simulation), remote laboratories (real equipment accessible at distance) and data sets from physical laboratory experiments (together called “online labs”) for large-scale use in education. In this way, Go-Lab enables inquiry-based learning that promotes acquisition of deep conceptual domain knowledge and inquiry skills, with the further intent of interesting students in careers in science. For students, Go-Lab offers the opportunity to perform scientific experiments with online labs in pedagogically structured learning spaces. Go-Lab’s inquiry learning spaces (ILSs) structure the students’ inquiry process through an inquiry cycle and provide students with guidance...

20. Design of turbulent tangential micro-mixers that mix liquids on the nanosecond time scale - Mitic, Sandra; Nieuwkasteele, Jan W. van; Berg, Albert van den; Vries, Simon de
Unravelling (bio)chemical reaction mechanisms and macromolecular folding pathways on the (sub)microsecond time scale is limited by the time resolution of kinetic instruments for mixing reactants and observation of the progress of the reaction. To improve the mixing time resolution, turbulent four- and two-jet tangential micro-mixers were designed and characterized for their mixing and (unwanted) premixing performances employing acid-base reactions monitored by a pH-sensitive fluorescent dye. The mixing performances of the micro-mixers were determined after the mixing chamber in a free-flowing jet. The premixing behavior in the vortex chamber was assessed in an optically transparent glass-silicon replica of a previously well-characterized...

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