312 research outputs found
Dean flow focusing and separation of small microspheres within a narrow size range.
Copyright The Author(s) 2014. This article is published with open access at Springerlink.com. This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are creditedRapid, selective particle separation and concentration within the bacterial size range (1–3 μm) in clinical or environmental samples promises significant improvements in detection of pathogenic microorganisms in areas including diagnostics and bio-defence. It has been proposed that microfluidic Dean flow-based separation might offer simple, efficient sample clean-up: separation of larger, bioassay contaminants to prepare bioassay targets including spores, viruses and proteins. However, reports are limited to focusing spherical particles with diameters of 5 μm or above. To evaluate Dean flow separation for (1–3 μm) range samples, we employ a 20 μm width and depth, spiral microchannel. We demonstrate focusing, separation and concentration of particles with closely spaced diameters of 2.1 and 3.2 μm, significantly smaller than previously reported as separated in Dean flow devices. The smallest target, represented by 1.0 μm particles, is not focused due to the high pressures associated with focussing particles of this size; however, it is cleaned of 93 % of 3.2 μm and 87 % of 2.1 μm microparticles. Concentration increases approaching 3.5 times, close to the maximum, were obtained for 3.2 μm particles at a flow rate of 10 μl min−1. Increasing concentration degraded separation, commencing at significantly lower concentrations than previously predicted, particularly for particles on the limit of being focused. It was demonstrated that flow separation specificity can be fine-tuned by adjustment of output pressure differentials, improving separation of closely spaced particle sizes. We conclude that Dean flow separation techniques can be effectively applied to sample clean-up within this significant microorganism size range.Peer reviewedFinal Published versio
Fully integrated digital microfluidics platform for automated immunoassay; a versatile tool for rapid, specific detection of a wide range of pathogens
© 2018 Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence http://creativecommons.org/licenses/by-nc-nd/4.0/.With the tangible threat posed by the release of chemical and biological warfare (CBW) agents, detection of airborne pathogens is a critical military and security concern. Recent air sampling techniques developed for biocollection take advantage of Electrowetting on Dielectric (EWOD) to recover material, producing highly concentrated droplet samples. Bespoke EWOD-based digital microfluidics platforms are very well suited to take full advantage of the microlitre concentrated droplet resulting from this recovery process. In this paper we present a free-standing, fully automated DMF platform for immunoassay. Using this system, we demonstrate the automated detection of four classes of CBW agent simulant biomolecules and organisms each representing credible threat agents. Taking advantage of the full magnetic separation process with antibody-bound microbeads, rapid and complete separation of specific target antigen can be achieved with minimal washing steps allowing for very rapid detection. Here, we report clear detection of four categories of antigens achieved with assay completion times of between six and ten minutes. Detection of HSA, Bacillus atrophaeus (BG spores), MS2 bacteriophage and Escherichia coli are demonstrated with estimated limit of detection of respectively 30 ng ml -1, 4 × 10 4 cfu ml -1, 10 6 pfu ml -1 and 2 × 10 7 cfu ml -1. The fully-integrated portable platform described in this paper is highly compatible with the next generation of electrowetting-coupled air samplers and thus shows strong potential toward future in-field deployable biodetection systems and could have key implication in life-changing sectors such as healthcare, environment or food security.Peer reviewe
Electrowetting-Based Digital Microfluidics Platform for Automated Enzyme-linked Immunosorbent Assay
Electrowetting is the effect by which the contact angle of a droplet exposed to a surface charge is modified. Electrowetting-on-dielectric (EWOD) exploits the dielectric properties of thin insulator films to enhance the charge density and hence boost the electrowetting effect. The presence of charges results in an electrically induced spreading of the droplet which permits purposeful manipulation across a hydrophobic surface. Here, we demonstrate EWOD-based protocol for sample processing and detection of four categories of antigens, using an automated surface actuation platform, via two variations of an Enzyme-Linked Immunosorbent Assay (ELISA) methods. The ELISA is performed on magnetic beads with immobilized primary antibodies which can be selected to target a specific antigen. An antibody conjugated to HRP binds to the antigen and is mixed with H 2O 2/Luminol for quantification of the captured pathogens. Assay completion times of between 6 and 10 min were achieved, whilst minuscule volumes of reagents were utilized.Peer reviewe
Simulation and optimisation of terahertz emission from InGaAs and InP photoconductive switches
We simulate the terahertz emission from laterally-biased InGaAs and InP using
a three-dimensional carrier dynamics model in order to optimise the
semiconductor material. Incident pump-pulse parameters of current Ti:Sapphire
and Er:fibre lasers are chosen, and the simulation models the semiconductor's
bandstructure using parabolic Gamma, L and X valleys, and heavy holes. The
emitted terahertz radiation is propagated within the semiconductor and into
free space using a model based on the Drude-Lorentz dielectric function. As the
InGaAs alloy approaches InAs an increase in the emitted power is observed, and
this is attributed to a greater electron mobility. Additionally,
low-temperature grown and ion-implanted InGaAs are modelled using a finite
carrier trapping time. At sub-picosecond trapping times the terahertz bandwidth
is found to increase significantly at the cost of a reduced emission power.Comment: 9 pages, 7 figure
Protein droplet actuation on superhydrophobic surfaces: A new approach toward anti-biofouling electrowetting systems
© 2017 The Royal Society of Chemistry. This is an Open Access article, distributed under the terms of the Creative Commons Attribution 3.0 Unported (CC BY 3.0) licence https://creativecommons.org/licenses/by/3.0/.Among Lab-on-a-chip techniques, Digital microfluidics (DMF), allowing the precise actuation of discrete droplets, is a highly promising, flexible, biochemical assay platform for biomedical and bio-detection applications. However the durability of DMF systems remains a challenge due to biofouling of the droplet-actuating surface when high concentrations of biomolecules are employed. To address this issue, the use of superhydrophobic materials as the actuating surface in DMF devices is examined. The change in contact angle by electrowetting of deionised water and ovalbumin protein samples is characterised on different surfaces (hydrophobic and superhydrophobic). Ovalbumin droplets at 1 mg ml-1 concentration display better electrowetting reversibility on Neverwet®, a commercial superhydrophobic material, than on Cytop®, a typical DMF hydrophobic material. Biofouling rate, characterised by roll-off angle measurement of ovalbumin loaded droplets and further confirmed by measurements of the mean fluorescence intensity of labelled fibrinogen, appears greatly reduced on Neverwet®. Transportation of protein laden droplets (fibrinogen at concentration 0.1 mg ml-1 and ovalbumin at concentration 1 mg ml-1 and 10 mg ml-1) is successfully demonstrated using electrowetting actuation on both single-plate and parallel-plate configurations with performance comparable to that of DI water actuation. In addition, although droplet splitting requires further attention, merging and efficient mixing are demonstrated.Peer reviewe
Protein droplet actuation on superhydrophobic surfaces: A new approach toward anti-biofouling electrowetting systems
Among Lab-on-a-chip techniques, digital microfluidics (DMF), allowing the precise actuation of discrete droplets, is a highly promising, flexible, biochemical assay platform for biomedical and bio-detection applications. However the durability of DMF systems remains a challenge due to biofouling of the droplet-actuating surface when high concentrations of biomolecules are employed. To address this issue, the use of superhydrophobic materials as the actuating surface in DMF devices is examined. The change in contact angle by electrowetting of deionised water and ovalbumin protein samples is characterised on different surfaces (hydrophobic and superhydrophobic). Ovalbumin droplets at 1 mg ml−1 concentration display better electrowetting reversibility on Neverwet®, a commercial superhydrophobic material, than on Cytop®, a typical DMF hydrophobic material. Biofouling rate, characterised by roll-off angle measurement of ovalbumin loaded droplets and further confirmed by measurements of the mean fluorescence intensity of labelled fibrinogen, appears greatly reduced on Neverwet®. Transportation of protein laden droplets (fibrinogen at concentration 0.1 mg ml−1 and ovalbumin at concentration 1 mg ml−1 and 10 mg ml−1) is successfully demonstrated using electrowetting actuation on both single-plate and parallel-plate configurations with performance comparable to that of DI water actuation. In addition, although droplet splitting requires further attention, merging and efficient mixing are demonstrated
Isotopic Scaling of Heavy Projectile Residues from the collisions of 25 MeV/nucleon 86Kr with 124Sn, 112Sn and 64Ni, 58Ni
The scaling of the yields of heavy projectile residues from the reactions of
25 MeV/nucleon 86Kr projectiles with 124Sn,112Sn and 64Ni, 58Nitargets is
studied. Isotopically resolved yield distributions of projectile fragments in
the range Z=10-36 from these reaction pairs were measured with the MARS recoil
separator in the angular range 2.7-5.3 degrees. The velocities of the residues,
monotonically decreasing with Z down to Z~26-28, are employed to characterize
the excitation energy. The yield ratios R21(N,Z) for each pair of systems are
found to exhibit isotopic scaling (isoscaling), namely, an exponential
dependence on the fragment atomic number Z and neutron number N. The isoscaling
is found to occur in the residue Z range corresponding to the maximum observed
excitation energies. The corresponding isoscaling parameters are alpha=0.43 and
beta=-0.50 for the Kr+Sn system and alpha=0.27 and beta=-0.34 for the Kr+Ni
system. For the Kr+Sn system, for which the experimental angular acceptance
range lies inside the grazing angle, isoscaling was found to occur for Z<26 and
N<34. For heavier fragments from Kr+Sn, the parameters vary monotonically,
alpha decreasing with Z and beta increasing with N. This variation is found to
be related to the evolution towards isospin equilibration and, as such, it can
serve as a tracer of the N/Z equilibration process. The present heavy-residue
data extend the observation of isotopic scaling from the intermediate mass
fragment region to the heavy-residue region. Such high-resolution mass
spectrometric data can provide important information on the role of isospin in
peripheral and mid-peripheral collisions, complementary to that accessible from
modern large-acceptance multidetector devices.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
Tractarian Objects and Logical Categories
It has been much debated whether Tractarian objects are what Russell would have called particulars or whether they include also properties and relations. This paper claims that the debate is misguided: there is no logical category such that Wittgenstein intended the reader of the Tractatus to understand his objects either as providing examples of or as not providing examples of that category. This is not to say that Wittgenstein set himself against the very idea of a logical category: quite the contrary. However, where Russell presents his logical variety of particulars and the various types of universal, and Frege presents his of objects and the various types of function, Wittgenstein denies the propriety of such a priori expositions. Wittgenstein envisages a variety of logical types of entity but insists that the nature of these types is something to be discovered only through analysis
Mass Parameterizations and Predictions of Isotopic Observables
We discuss the accuracy of mass models for extrapolating to very asymmetric
nuclei and the impact of such extrapolations on the predictions of isotopic
observables in multifragmentation. We obtain improved mass predictions by
incorporating measured masses and extrapolating to unmeasured masses with a
mass formula that includes surface symmetry and Coulomb terms. We find that
using accurate masses has a significant impact on the predicted isotopic
observables.Comment: 12 pages, 4 figure
Interpretation of specific heat and spontaneous magnetization anomalies at the re-entrant Superconducting-ferromagnetic transition in (Ho0.6Er0.4)Rh4B4
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