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Now showing 1 - 10 of 75
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    Label free sensing of creatinine using a 6 GHz CMOS near-field dielectric immunosensor
    (Cambridge : Royal Society of Chemistry, 2015) Guha, S.; Warsinke, A.; Tientcheu, Ch.M.; Schmalz, K.; Meliani, C.; Wenger, Ch.
    In this work we present a CMOS high frequency direct immunosensor operating at 6 GHz (C-band) for label free determination of creatinine. The sensor is fabricated in standard 0.13 μm SiGe:C BiCMOS process. The report also demonstrates the ability to immobilize creatinine molecules on a Si3N4 passivation layer of the standard BiCMOS/CMOS process, therefore, evading any further need of cumbersome post processing of the fabricated sensor chip. The sensor is based on capacitive detection of the amount of non-creatinine bound antibodies binding to an immobilized creatinine layer on the passivated sensor. The chip bound antibody amount in turn corresponds indirectly to the creatinine concentration used in the incubation phase. The determination of creatinine in the concentration range of 0.88–880 μM is successfully demonstrated in this work. A sensitivity of 35 MHz/10 fold increase in creatinine concentration (during incubation) at the centre frequency of 6 GHz is gained by the immunosensor. The results are compared with a standard optical measurement technique and the dynamic range and sensitivity is of the order of the established optical indication technique. The C-band immunosensor chip comprising an area of 0.3 mm2 reduces the sensing area considerably, therefore, requiring a sample volume as low as 2 μl. The small analyte sample volume and label free approach also reduce the experimental costs in addition to the low fabrication costs offered by the batch fabrication technique of CMOS/BiCMOS process.
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    High spatial and temporal resolution cell manipulation techniques in microchannels
    (Cambridge : Royal Society of Chemistry, 2016) Novo, Pedro; Dell’Aica, Margherita; Janasek, Dirk; Zahedi, René P.
    The advent of microfluidics has enabled thorough control of cell manipulation experiments in so called lab on chips. Lab on chips foster the integration of actuation and detection systems, and require minute sample and reagent amounts. Typically employed microfluidic structures have similar dimensions as cells, enabling precise spatial and temporal control of individual cells and their local environments. Several strategies for high spatio-temporal control of cells in microfluidics have been reported in recent years, namely methods relying on careful design of the microfluidic structures (e.g. pinched flow), by integration of actuators (e.g. electrodes or magnets for dielectro-, acousto- and magneto-phoresis), or integrations thereof. This review presents the recent developments of cell experiments in microfluidics divided into two parts: an introduction to spatial control of cells in microchannels followed by special emphasis in the high temporal control of cell-stimulus reaction and quenching. In the end, the present state of the art is discussed in line with future perspectives and challenges for translating these devices into routine applications.
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    Analysis of fatty acids and triacylglycerides by Pd nanoparticle-assisted laser desorption/ionization mass spectrometry
    (Cambridge : Royal Society of Chemistry, 2015) Silina, Yuliya E.; Fink-Straube, Claudia; Hayen, Heiko; Volmer, Dietrich A.
    In this study, we propose a simple and rapid technique for characterization of free fatty acids and triacylglycerides (TAG) based on palladium nanoparticular (Pd-NP) surface-assisted laser desorption/ionization (SALDI) mass spectrometry (MS). The implemented Pd-NP material allowed detection of free fatty acids and TAGs exclusively as [M + K]+ ions in positive ion mode. Under negative ionization conditions, unusual trimetric structures were generated for free fatty acids, while TAGs underwent irreproducible degradation reactions. Importantly, the mass spectra obtained from Pd-NP targets in positive ion mode were very clean without interferences from matrix-derived ions in the low m/z range and readily enabled the detection of intact TAGs in vegetable oils without major fragmentation reactions as compared to conventional MALDI-MS, requiring only a minimal amount of sample preparation.
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    Direction specific adhesion induced by subsurface liquid filled microchannels
    (Cambridge : Royal Society of Chemistry, 2012) Majumder, Abhijit; Mondal, Subrata; Tiwari, Anurag Kumar; Ghatak, Animangsu; Sharma, Ashutosh
    While directional effects in adhesion and locomotion have in general been generated by creating symmetry breaking topographic features on the surface of a soft bodied object, here we present a novel method for imparting this effect to thin adhesive layers by embedding liquid filled microchannels arranged in pairs with specific intra and inter pair distances. The adhesive exhibits uniform adhesion in classical peel tests when both the channels are filled with either air or a wetting liquid. But the asymmetric effect shows up when only one of the channels in the pair is filled with the liquid. The liquid alters the surface tension of the inner wall of the channel, which results in bulging deformation of the thin skin of the adhesive over the channel. The bulging however remains asymmetric, the extent of asymmetry depending on the intra-pair spacing between the channels. Besides the bulging effect, filling in one channel of a pair with liquid also leads to an asymmetric variation in its modulus. As a result, when an adherent is peeled off the adhesive from two opposite directions, significantly different adhesion strengths result. A similar directional effect also results when channels of two different diameters are used in the pair, thus opening up the possibility of generating several different adhesion strengths simply by altering the geometric features of the embedded microstructure and its filling status. We show also that for both channels in a pair filled with liquid, the adhesion strength increases significantly, by over 60 times of what is achieved for a smooth, featureless, adhesive layer.
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    On the behaviour of nanoparticles in oil-in-water emulsions with different surfactants
    (Cambridge : Royal Society of Chemistry, 2014) Lacava, Johann; Ouali, Ahmed-Amine; Raillard, Brice; Kraus, Tobias
    The distribution of narrowly dispersed gold nanoparticles in hexane-in-water emulsions was studied for different surfactants. Good surfactants such as SDS and Triton X-100 block the oil-water interfaces and confine particles in the droplet. Other surfactants (Tween 85 and Span 20) form synergistic mixtures with the nanoparticles at the interfaces that lower the surface tension more than any component. Supraparticles with fully defined particle distribution form in the droplets only for surfactants that block the interface. Other surfactants promote the formation of fcc agglomerates. Nanoparticles in emulsions behave markedly different from microparticles-their structure formation is governed by free energy minimization, while microparticles are dominated by kinetics.
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    Carbon onion–sulfur hybrid cathodes for lithium–sulfur batteries
    (Cambridge : Royal Society of Chemistry, 2017) Choudhury, Soumyadip; Zeiger, Marco; Massuti-Ballester, Pau; Fleischmann, Simon; Formanek, Petr; Borchardt, Lars; Presser, Volker
    In this study, we explore carbon onions (diameter below 10 nm), for the first time, as a substrate material for lithium sulfur cathodes. We introduce several scalable synthesis routes to fabricate carbon onion–sulfur hybrids by adopting in situ and melt diffusion strategies with sulfur fractions up to 68 mass%. The conducting skeleton of agglomerated carbon onions proved to be responsible for keeping active sulfur always in close vicinity to the conducting matrix. Therefore, the hybrids are found to be efficient cathodes for Li–S batteries, yielding 97–98% Coulombic efficiency over 150 cycles with a slow fading of the specific capacity (ca. 660 mA h g−1 after 150 cycles) in long term cycle test and rate capability experiments.
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    Fast IR laser mapping ellipsometry for the study of functional organic thin films
    (Cambridge : Royal Society of Chemistry, 2015) Furchner, Andreas; Sun, Guoguang; Ketelsen, Helge; Rappich, Jörg; Hinrichs, Karsten
    Fast infrared mapping with sub-millimeter lateral resolution as well as time-resolved infrared studies of kinetic processes of functional organic thin films require a new generation of infrared ellipsometers. We present a novel laboratory-based infrared (IR) laser mapping ellipsometer, in which a laser is coupled to a variable-angle rotating analyzer ellipsometer. Compared to conventional Fourier-transform infrared (FT-IR) ellipsometers, the IR laser ellipsometer provides ten- to hundredfold shorter measurement times down to 80 ms per measured spot, as well as about tenfold increased lateral resolution of 120 μm, thus enabling mapping of small sample areas with thin-film sensitivity. The ellipsometer, equipped with a HeNe laser emitting at about 2949 cm−1, was applied for the optical characterization of inhomogeneous poly(3-hexylthiophene) [P3HT] and poly(N-isopropylacrylamide) [PNIPAAm] organic thin films used for opto-electronics and bioapplications. With the constant development of tunable IR laser sources, laser-based infrared ellipsometry is a promising technique for fast in-depth mapping characterization of thin films and blends.
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    Surface-assisted laser desorption/ionization mass spectrometry using ordered silicon nanopillar arrays
    (Cambridge : Royal Society of Chemistry, 2014) Alhmoud, Hashim Z.; Guinan, Taryn M.; Elnathan, Roey; Kobus, Hilton; Voelcker, Nicolas H.
    Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is ideally suited for the high-throughput analysis of small molecules in bodily fluids (e.g. saliva, urine, and blood plasma). A key application for this technique is the testing of drug consumption in the context of workplace, roadside, athlete sports and anti-addictive drug compliance. Here, we show that vertically-aligned ordered silicon nanopillar (SiNP) arrays fabricated using nanosphere lithography followed by metal-assisted chemical etching (MACE) are suitable substrates for the SALDI-MS detection of methadone and small peptides. Porosity, length and diameter are fabrication parameters that we have explored here in order to optimize analytical performance. We demonstrate the quantitative analysis of methadone in MilliQ water down to 32 ng mL-1. Finally, the capability of SiNP arrays to facilitate the detection of methadone in clinical samples is also demonstrated.
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    Self-calibrating highly sensitive dynamic capacitance sensor: Towards rapid sensing and counting of particles in laminar flow systems
    (Cambridge : Royal Society of Chemistry, 2015) Guha, S.; Schmalz, K.; Wenger, Ch.; Herzel, F.
    In this report we propose a sensor architecture and a corresponding read-out technique on silicon for the detection of dynamic capacitance change. This approach can be applied to rapid particle counting and single particle sensing in a fluidic system. The sensing principle is based on capacitance variation of an interdigitated electrode (IDE) structure embedded in an oscillator circuit. The capacitance scaling of the IDE results in frequency modulation of the oscillator. A demodulator architecture is employed to provide a read-out of the frequency modulation caused by the capacitance change. A self-calibrating technique is employed at the read-out amplifier stage. The capacitance variation of the IDE due to particle flow causing frequency modulation and the corresponding demodulator read-out has been analytically modelled. Experimental verification of the established model and the functionality of the sensor chip were shown using a modulating capacitor independent of fluidic integration. The initial results show that the sensor is capable of detecting frequency changes of the order of 100 parts per million (PPM), which translates to a shift of 1.43 MHz at 14.3 GHz operating frequency. It is also shown that a capacitance change every 3 μs can be accurately detected.
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    An experimental study on the influence of trace impurities on ionization of atmospheric noble gas dielectric barrier discharges
    (Cambridge : Royal Society of Chemistry, 2016) Klute, F.D.; Schütz, A.; Michels, A.; Vadla, C.; Veza, D.; Horvatic, V.; Franzke, J.
    While the influence of trace impurities in noble gas discharges is well established in theoretical work, experimental approaches are difficult. Particularly the effects of trace concentrations of N2 on He discharges are complicated to investigate due to the fact that for He 5.0 the purity of He is only 99.999%. This corresponds to a residual concentration of 10 ppm, thereof 3 ppm of N2, in He. Matters are made difficult by the fact that He DBD plasmajets are normally operated under an ambient atmosphere, which has a high abundance of N2. This work tackles these problems from two sides. The first approach is to operate a DBD plasmajet under a quasi-controlled He atmosphere, therefore diminishing the effect of atmospheric N2 and making a defined contamination with N2 possible. The second approach is using Ar as the operating gas and introducing propane (C3H8) as a suitable substitute impurity like N2 in He. As will be shown both discharges in either He or Ar, with their respective impurity show the same qualitative behaviour.