High frequency dielectrophoretic response of microalgae over time.
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ABSTRACT:
SUBMITTER: Hadady H
PROVIDER: S-EPMC4526272 | biostudies-literature | 2014 Dec
REPOSITORIES: biostudies-literature
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Project description:We explore the use of dielectrophoresis to discern the electrical properties of single cells by observing them at multiple frequencies. We first simulate experimental conditions to show that as we increase the number of measured frequencies, we are able to better discriminate among different cells. Furthermore, we use the simulation to find the optimal number and value of frequencies to use to best discriminate among different cells in general. We then fabricate a microfluidic device, calibrate it with polystyrene beads, and characterize it with BA/F3 cells. With this device, we test three different activation levels of HL60 cells treated with cytochalasin D using the optimal frequency sequence obtained in simulation to determine the differences in discrimination abilities depending on the number of frequencies used. We quantify the discrimination abilities of the optimal one, two, and three frequencies by minimizing 0-1 loss.
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Project description:ObjectiveIncreased levels of reaction time variability (RTV) are characteristics of sustained attention deficits. The clinical significance of RTV has been widely recognized. However, the reliability of RTV measurements has not been widely studied. The present study aimed to assess the test-retest reliability of RTV conventional measurements, e.g., the standard deviation (SD), the coefficient of variation (CV), and a new measurement called the amplitude of low frequency fluctuation (ALFF) of RT. In addition, we aimed to assess differences and similarities of these measurements between different tasks.MethodThirty-seven healthy college students participated in 2 tasks, i.e., an Eriksen flanker task (EFT) and a simple reaction task (SRT), twice over a mean interval of 56 days. Conventional measurements of RTV including RT-SD and RT-CV were assessed first. Then the RT time series were converted into frequency domains, and RT-ALFF was further calculated for the whole frequency band (0.0023-0.167 Hz) and for a few sub-frequency bands including Slow-6 (<0.01 Hz), Slow-5 (0.01-0.027 Hz), Slow-4 (0.027-0.073 Hz), and Slow-3 (0.073-0.167 Hz). The test-retest reliability of these measurements was evaluated through intra-class correlation (ICC) tests. Differences and correlations between each EFT and SRT measurement were further examined during both visits.Results1) The RT-ALFF of the Slow-5/4/3 and conventional measurements of RT-SD and RT-CV showed moderate to high levels of test-retest reliability. EFT RT-ALFF patterns generated slightly higher ICC values than SRT values in higher frequency bands (Slow-3), but SRT RT-ALFF values showed slightly higher ICC values than EFT values in lower frequency bands (Slow-5 and Slow-4). 2) RT-ALFF magnitudes in each sub-frequency band were greater for the SRT than those for the EFT. 3) The RT-ALFF in the Slow-4 of the EFT was found to be correlated with the RT-ALFF in the Slow-5 of the SRT for both two visits, but no consistently significant correlation was found between the same frequency bands.ConclusionsThese findings reveal good test-retest reliability for conventional measurements and for the RT-ALFF of RTV. The RT-ALFF presented frequency-dependent similarities across tasks. All of our results reveal the presence of different frequency structures between the two tasks, and thus the frequency-dependent characteristics of different tasks deserve more attention in future studies.
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Project description:Phenotypic quantification of cells based on their plasma membrane capacitance and cytoplasmic conductivity, as determined by their dielectrophoretic frequency dispersion, is often used as a marker for their biological function. However, due to the prevalence of phenotypic heterogeneity in many biological systems of interest, there is a need for methods capable of determining the dielectrophoretic dispersion of single cells at high throughput and without the need for sample dilution. We present a microfluidic device methodology wherein localized constrictions in the microchannel are used to enhance the field delivered by adjoining planar electrodes, so that the dielectrophoresis level and direction on flow-focused cells can be determined on each traversing cell in a high-throughput manner based on their deflected flow streamlines. Using a sample of human red blood cells diluted to 2.25 × 108 cells/mL, the dielectrophoretic translation of single cells traversing at a flow rate of 1.68 μL/min is measured at a throughput of 1.1 × 105 cells/min, to distinguish positive versus negative dielectrophoresis and determine their crossover frequency in media of differing conductivity for validation of the computed membrane capacitance to that from prior methods. We envision application of this dynamic dielectrophoresis (Dy-DEP) method towards high-throughput measurement of the dielectric dispersion of single cells to stratify phenotypic heterogeneity of a particular sample based on their DEP crossover frequency, without the need for significant sample dilution. Grapical abstract.
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Project description:Alternating current (AC) dielectrophoresis (DEP) experiments for biological particles in microdevices are typically done at a fixed frequency. Reconstructing the DEP response curve from static frequency experiments is laborious, but essential to ascertain differences in dielectric properties of biological particles. Our lab explored the concept of sweeping the frequency as a function of time to rapidly determine the DEP response curve from fewer experiments. For the purpose of determining an ideal sweep rate, homogeneous 6.08 μm polystyrene (PS) beads were used as a model system. Translatability of the sweep rate approach to ∼7 μm red blood cells (RBC) was then verified. An Au/Ti quadrapole electrode microfluidic device was used to separately subject particles and cells to 10Vpp AC electric fields at frequencies ranging from 0.010 to 2.0 MHz over sweep rates from 0.00080 to 0.17 MHz/s. PS beads exhibited negative DEP assembly over the frequencies explored due to Maxwell-Wagner interfacial polarizations. Results demonstrate that frequency sweep rates must be slower than particle polarization timescales to achieve reliable incremental polarizations; sweep rates near 0.00080 MHz/s yielded DEP behaviors very consistent with static frequency DEP responses for both PS beads and RBCs.
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Project description:We present an automated dielectrophoretic assisted cell sorting (DACS) device for dielectric characterization and isolation of neural cells. Dielectrophoretic (DEP) principles are often used to develop cell sorting techniques. Here we report the first statistically significant neuronal sorting using DACS to enrich neurons from a heterogeneous population of mouse derived neural stem/progenitor cells (NSPCs) and neurons. We also study the dielectric dispersions within a heterogeneous cell population using a Monte-Carlo (MC) simulation. This simulation model explains the trapping behavior of populations as a function of frequency and predicts sorting efficiencies. The platform consists of a DEP electrode array with three multiplexed trapping regions that can be independently activated at different frequencies. A novel microfluidic manifold enables cell sorting by trapping and collecting cells at discrete frequency bands rather than single frequencies. The device is used to first determine the percentage of cells trapped at these frequency bands. With this characterization and the MC simulation we choose the optimal parameters for neuronal sorting. Cell sorting experiments presented achieve a 1.4-fold neuronal enrichment as predicted by our model.
| S-EPMC5493482 | biostudies-literature
Project description:Separation of (biological) particles ([Formula: see text]) according to size or other properties is an ongoing challenge in a variety of technical relevant fields. Dielectrophoresis is one method to separate particles according to a diversity of properties, and within the last decades a pool of dielectrophoretic separation techniques has been developed. However, many of them either suffer selectivity or throughput. We use simulation and experiments to investigate retention mechanisms in a novel DEP scheme, namely, frequency-modulated DEP. Results from experiments and simulation show a good agreement for the separation of binary PS particles mixtures with respect to size and more importantly, for the challenging task of separating equally sized microparticles according to surface functionalization alone. The separation with respect to size was performed using 2 [Formula: see text]m and 3 [Formula: see text]m sized particles, whereas separation with respect to surface functionalization was performed with 2 [Formula: see text]m particles. The results from this study can be used to solve challenging separation tasks, for example to separate particles with distributed properties.
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Project description:ObjectiveTo investigate whether later high school start time is associated with lower migraine frequency in high school students with migraine.BackgroundAdequate sleep is thought to be important in managing adolescent migraine. The American Academy of Sleep Medicine recommends teenagers sleep ≥8 hours/night. Adolescents have a physiologically delayed sleep phase, going to bed, and waking later than children and adults. The American Academy of Pediatrics (AAP) accordingly recommends high schools start no earlier than 8:30 AM.MethodsCross-sectional observational study of U.S. high schoolers with migraine. Participants were recruited nationally using social media. Respondents attending high schools starting at 8:30 AM or later were compared to those attending earlier start time schools. The primary outcome was headache days/month.ResultsTwo hundred and fifty-six subjects constituted the analysis set: 115 later group vs 141 earlier group. Age and sex did not differ. Mean (SD) self-reported headache days/month were 7 (5) vs 8 (7), respectively, (P = .985); mean difference (95% CI for the difference) was -0.8 (-2.3-0.7) days. Median (IQR) self-reported total hours of sleep/school night were: 5.6 (5.0-6.6) vs 5.6 (4.5-6.4), P = .058. Students attending later start time schools woke later (median [IQR] 6:38 AM [55 minutes] vs 6:09 AM [59 minutes], P < .0001) and left home later (median [IQR] 7:28 AM [28 minutes] vs 7:02 AM [60 minutes], P < .0001). Average commute time was also longer: 41 (21) minutes vs 28 (16), P < .0001. The vast majority in both groups reported missing breakfast at least once/week: 103/114 (90.4%) vs 128/141 (90.8%), P = .907. Hours of sleep did not correlate with headache days per month.ConclusionHigh school start time does not have a large effect on headache frequency in high schoolers with migraine. Given the high variance in headache days/month observed in this study, a larger study would be needed to determine whether there might still be a small effect of starting high school at/after 8:30 AM. More research is needed to establish evidence-based recommendations about lifestyle factors in adolescent migraine management.
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