| 1. |
- Akbari, Elham, et al.
(author)
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SEPARATION OF SINGLETS AND CLUSTERS OF GROUP A STREPTOCOCCI USING DETERMINISTIC LATERAL DISPLACEMENT AND FILTER SONICATION
- 2022
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In: MicroTAS 2022 - 26th International Conference on Miniaturized Systems for Chemistry and Life Sciences. - 9781733419048 ; , s. 306-307
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Conference paper (peer-reviewed)abstract
- Differences in morphologies of bacteria and bacteria clusters are thought to contribute to their virulence and colonization. However, the conventional standard cell biological methods cannot separate bacteria and bacteria clusters based on their morphologies and sizes, making studies of the underlying mechanisms difficult. Here we report a simple label-free method for the continuous separation of singlets and clusters, of group A streptococci, based on their size and morphology, using Deterministic Lateral Displacement and filter-sonication. In general, this opens up for the generation of cell populations with heterogenicity in cluster size and physical properties.
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| 2. |
- Beech, Jason P., et al.
(author)
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Electrokinetic wall effect mechanisms and applications
- 2020
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In: MicroTAS 2020 - 24th International Conference on Miniaturized Systems for Chemistry and Life Sciences. - 9781733419017 ; , s. 42-43
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Conference paper (peer-reviewed)abstract
- Under the application of longitudinal electric fields in microchannels, microparticles experience lift forces that push them away from the channel walls and affect their trajectories. At high frequencies (>100KHz) the dielectrophoretic forces dominate and are well understood but at lower frequencies there is little agreement as to the exact nature of the forces, how they are generated and how they vary due to the many different experimental conditions that are used in microfluidics devices. Here we present an experimental study of these mechanisms.
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| 3. |
- Beech, Jason P, et al.
(author)
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Using symmetry to control viscoelastic waves in pillar arrays
- 2023
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In: RSC Advances. - 2046-2069. ; 13:45, s. 31497-31506
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Journal article (peer-reviewed)abstract
- Solutions of macromolecules exhibit viscoelastic properties and unlike Newtonian fluids, they may break time-reversal symmetry at low Reynolds numbers resulting in elastic turbulence. Furthermore, under some conditions, instead of the chaotic turbulence, the result is large-scale waves in the form of cyclic spatial and temporal concentration variations, as has been shown for macromolecular DNA flowing in microfluidic pillar arrays. We here demonstrate how altering the symmetry of the individual pillars can be used to influence the symmetry of these waves. We control the extent of instabilities in viscoelastic flow by leveraging the effects of the symmetry of the pillars on the waves, demonstrating suppressed viscoelastic fluctuations with relevance for transport and sorting applications, or conversely opening up for enhanced viscoelasticity-mediated mixing. The onset of waves, which changes flow resistance, occurs at different Deborah numbers for flow in different directions through the array of triangular pillars, thus breaking the symmetry of the flow resistance along the device, opening up for using the occurrence of the waves to construct a fluidic diode.
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| 4. |
- Ho, Bao D., et al.
(author)
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Cell sorting using electrokinetic deterministic lateral displacement
- 2020
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In: Micromachines. - : MDPI AG. - 2072-666X. ; 12:1
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Journal article (peer-reviewed)abstract
- We show that by combining deterministic lateral displacement (DLD) with electrokinetics, it is possible to sort cells based on differences in their membrane and/or internal structures. Using heat to deactivate cells, which change their viability and structure, we then demonstrate sorting of a mixture of viable and non-viable cells for two different cell types. For Escherichia coli, the size change due to deactivation is insufficient to allow size-based DLD separation. Our method instead leverages the considerable change in zeta potential to achieve separation at low frequency. Conversely, for Saccharomyces cerevisiae (Baker’s yeast) the heat treatment does not result in any significant change of zeta potential. Instead, we perform the sorting at higher frequency and utilize what we believe is a change in dielectrophoretic mobility for the separation. We expect our work to form a basis for the development of simple, low-cost, continuous label-free methods that can separate cells and bioparticles based on their intrinsic properties.
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| 5. |
- Ho, Bao D., et al.
(author)
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Charge-based separation of micro-and nanoparticles
- 2020
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In: Micromachines. - : MDPI AG. - 2072-666X. ; 11:11
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Journal article (peer-reviewed)abstract
- Deterministic Lateral Displacement (DLD) is a label-free particle sorting method that separates by size continuously and with high resolution. By combining DLD with electric fields (eDLD), we show separation of a variety of nano and micro-sized particles primarily by their zeta potential. Zeta potential is an indicator of electrokinetic charge—the charge corresponding to the electric field at the shear plane—an important property of micro-and nanoparticles in colloidal or separation science. We also demonstrate proof of principle of separation of nanoscale liposomes of different lipid compositions, with strong relevance for biomedicine. We perform careful characterization of relevant experimental conditions necessary to obtain adequate sorting of different particle types. By choosing a combination of frequency and amplitude, sorting can be made sensitive to the particle subgroup of interest. The enhanced displacement effect due to electrokinetics is found to be significant at low frequency and for particles with high zeta potential. The effect appears to scale with the square of the voltage, suggesting that it is associated with either non-linear electrokinetics or dielectrophoresis (DEP). However, since we observe large changes in separation behavior over the frequency range at which DEP forces are expected to remain constant, DEP can be ruled out.
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| 6. |
- Ho, Bao D., et al.
(author)
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High throughput extracellular vesicle sorting using electrokinetic deterministic lateral displacement
- 2020
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In: MicroTAS 2020 - 24th International Conference on Miniaturized Systems for Chemistry and Life Sciences. - 9781733419017 ; , s. 637-638
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Conference paper (peer-reviewed)abstract
- We present a microfluidic device that can sort nanosized extracellular vesicles (EVs) based on electrokinetics and Deterministic Lateral Displacement (DLD). The device is made from PDMS using standard soft-lithography, can separate particles down to 200 nm, and what is more, can achieve almost two orders of magnitude higher throughput than an otherwise single electrokinetic DLD device.
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| 7. |
- Hochstetter, Axel, et al.
(author)
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Deterministic Lateral Displacement : Challenges and Perspectives
- 2020
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 14:9, s. 10784-10795
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Research review (peer-reviewed)abstract
- The advent of microfluidics in the 1990s promised a revolution in multiple industries from healthcare to chemical processing. Deterministic lateral displacement (DLD) is a continuous-flow microfluidic particle separation method discovered in 2004 that has been applied successfully and widely to the separation of blood cells, yeast, spores, bacteria, viruses, DNA, droplets, and more. Deterministic lateral displacement is conceptually simple and can deliver consistent performance over a wide range of flow rates and particle concentrations. Despite wide use and in-depth study, DLD has not yet been fully elucidated or optimized, with different approaches to the same problem yielding varying results. We endeavor here to provide up-to-date expert opinion on the state-of-art and current fundamental, practical, and commercial challenges with DLD as well as describe experimental and modeling opportunities. Because these challenges and opportunities arise from constraints on hydrodynamics, fabrication, and operation at the micro- and nanoscale, we expect this Perspective to serve as a guide for the broader micro- and nanofluidic community to identify and to address open questions in the field.
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| 8. |
- Kesarimangalam, Sriram, 1983, et al.
(author)
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Fluorescence Microscopy of Nanochannel-Confined DNA
- 2024
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In: Methods in Molecular Biology. - 1940-6029 .- 1064-3745. - 9781071633779 - 9781071633762 ; , s. 175-202
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Book chapter (other academic/artistic)abstract
- Stretching of DNA in nanoscale confinement allows for several important studies. The genetic contents of the DNA can be visualized on the single DNA molecule level, and the polymer physics of confined DNA and also DNA/protein and other DNA/DNA-binding molecule interactions can be explored. This chapter describes the basic steps to fabricate the nanostructures, perform the experiments, and analyze the data.
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| 9. |
- Krog, Jens, et al.
(author)
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Photophysical image analysis : Unsupervised probabilistic thresholding for images from electron-multiplying charge-coupled devices
- 2024
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In: PLoS ONE. - 1932-6203. ; 19:4, s. 0300122-0300122
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Journal article (peer-reviewed)abstract
- We introduce the concept photophysical image analysis (PIA) and an associated pipeline for unsupervised probabilistic image thresholding for images recorded by electron-multiplying charge-coupled device (EMCCD) cameras. We base our approach on a closed-form analytic expression for the characteristic function (Fourier-transform of the probability mass function) for the image counts recorded in an EMCCD camera, which takes into account both stochasticity in the arrival of photons at the imaging camera and subsequent noise induced by the detection system of the camera. The only assumption in our method is that the background photon arrival to the imaging system is described by a stationary Poisson process (we make no assumption about the photon statistics for the signal). We estimate the background photon statistics parameter, λbg, from an image which contains both background and signal pixels by use of a novel truncated fit procedure with an automatically determined image count threshold. Prior to this, the camera noise model parameters are estimated using a calibration step. Utilizing the estimates for the camera parameters and λbg, we then introduce a probabilistic thresholding method, where, for the first time, the fraction of misclassified pixels can be determined a priori for a general image in an unsupervised way. We use synthetic images to validate our a priori estimates and to benchmark against the Otsu method, which is a popular unsupervised non-probabilistic image thresholding method (no a priori estimates for the error rates are provided). For completeness, we lastly present a simple heuristic general-purpose segmentation method based on the thresholding results, which we apply to segmentation of synthetic images and experimental images of fluorescent beads and lung cell nuclei. Our publicly available software opens up for fully automated, unsupervised, probabilistic photophysical image analysis.
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| 10. |
- Lard, Mercy, et al.
(author)
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Use of dielectrophoresis for directing T cells to microwells before nanostraw transfection : modelling and experiments
- 2022
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In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 12:47, s. 30295-30303
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Journal article (peer-reviewed)abstract
- Nanostraw substrates have great potential for achieving minimally invasive cell transfection. Cells located on the nanostraw substrate are subjected to mild DC electric pulses applied across the nanostraw substrate, which open pores in the cell membrane on top of the nanostraws and drives charged cargo through these pores via electrophoresis. However, with this method, the current may leak through uncovered nanostraws, thereby decreasing the desired effect in the cell-covered nanostraws. A minimization of the number of uncovered nanostraws could be achieved by high cell coverage, but this is challenging when working with small cell populations. Nanostraw substrates of smaller area could be covered by smaller cell populations but are hard to integrate into fluidics systems. Here, we use simulations and experiments to show that this issue can be addressed by covering the nanostraw substrate with an insulating layer containing pores of similar size to cells. The pores act as traps into which cells can be guided using dielectrophoresis, ensuring a high degree of occupancy while maintaining a high cell viability, even if the total number of cells is low.
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