Dielectrophoresis of nanocolloids: a molecular dynamics study

Dielectrophoresis (DEP), the motion of polarizable particles in non-uniform electric fields, has become an important tool for the transport, separation, and characterization of microparticles in biomedical and nanoelectronics research. In this article we present, to our knowledge, the first molecular dynamics simulations of DEP of nanometer-sized colloidal particles. We introduce a simplified model for polarizable nanoparticles, consisting of a large charged macroion and oppositely charged microions, in an explicit solvent. The model is then used to study DEP motion of the particle at different combinations of temperature and electric field strength. In accord with linear response theory, the particle drift velocities are shown to be proportional to the DEP force. Analysis of the colloid DEP mobility shows a clear time dependence, demonstrating the variation of friction under non-equilibrium. The time dependence of the mobility further results in an apparent weak variation of the DEP displacements with temperature

Diesel exhaust and house dust mite allergen lead to common changes in the airway methylome and hydroxymethylome.

Exposures to diesel exhaust particles (DEP) from traffic and house dust mite (HDM) allergens significantly increase risks of airway diseases, including asthma. This negative impact of DEP and HDM may in part be mediated by epigenetic mechanisms. Beyond functioning as a mechanical barrier, airway epithelial cells provide the first line of immune defense towards DEP and HDM exposures. To understand the epigenetic responses of airway epithelial cells to these exposures, we exposed human bronchial epithelial cells to DEP and HDM and studied genome-wide 5-methyl-cytosine (5mC) and 5-hydroxy-methylcytosine (5hmC) at base resolution. We found that exposures to DEP and HDM result in elevated TET1 and DNMT1 expression, associated with 5mC and 5hmC changes. Interestingly, over 20% of CpG sites are responsive to both exposures and changes in 5mC at these sites negatively correlated with gene expression differences. These 5mC and 5hmC changes are located in genes and pathways related to oxidative stress responses, epithelial function and immune cell responses and are enriched for binding sites of transcription factors (TFs) involved in these pathways. Histone marks associated with promoters, enhancers and actively transcribed gene bodies were associated with exposure-induced DNA methylation changes. Collectively, our data suggest that exposures to DEP and HDM alter 5mC and 5hmC levels at regulatory regions bound by TFs, which coordinate with histone marks to regulate gene networks of oxidative stress responses, epithelial function and immune cell responses. These observations provide novel insights into the epigenetic mechanisms that mediate the epithelial responses to DEP and HDM in airways

Dielectrophoresis of charged colloidal suspensions

We present a theoretical study of dielectrophoretic (DEP) crossover spectrum of two polarizable particles under the action of a nonuniform AC electric field. For two approaching particles, the mutual polarization interaction yields a change in their respective dipole moments, and hence, in the DEP crossover spectrum. The induced polarization effects are captured by the multiple image method. Using spectral representation theory, an analytic expression for the DEP force is derived. We find that the mutual polarization effects can change the crossover frequency at which the DEP force changes sign. The results are found to be in agreement with recent experimental observation and as they go beyond the standard theory, they help to clarify the important question of the underlying polarization mechanisms

Trapping cortical rat neurons

Cortical rat neurons were trapped by dielectrophoresis (DEP). Experimental data were compared with theoretically deduced relationships. The neuron was represented by a single-shell model. A planar quadrupole electrode structure was used for the creation of a nonuniform field. The electrode structure was modeled as four point charges. The experimental data did almost completely fit the theoretical yield/time relationship. The theoretical yield/amplitude relationship, however, did only apply for a restricted amount of frequencies. The experimental frequency behaviour (i.e., the DEP-spectrum) did not apply to the theory. A difference in neuronal physiological state can produce different DEP-spectra. For two frequencies (10 kHz and 14 MHz) adhesion to the substrate and outgrowth of the neurons was investigate

Escape from an optoelectronic tweezer trap: experimental results and simulations

Optoelectronic tweezers (OET) are a microsystem actuation technology capable of moving microparticles at mm s−1 velocities with nN forces. In this work, we analyze the behavior of particles manipulated by negative dielectrophoresis (DEP) forces in an OET trap. A user-friendly computer interface was developed to generate a circular rotating light pattern to control the movement of the particles, allowing their force profiles to be conveniently measured. Three-dimensional simulations were carried out to clarify the experimental results, and the DEP forces acting on the particles were simulated by integrating the Maxwell stress tensor. The simulations matched the experimental results and enabled the determination of a new “hopping” mechanism for particle-escape from the trap. As indicated by the simulations, there exists a vertical DEP force at the edge of the light pattern that pushes up particles to a region with a smaller horizontal DEP force. We propose that this phenomenon will be important to consider for the design of OET micromanipulation experiments for a wide range of applications

Localized Dielectric Loss Heating in Dielectrophoresis Devices

Temperature increases during dielectrophoresis (DEP) can affect the response of biological entities, and ignoring the effect can result in misleading analysis. The heating mechanism of a DEP device is typically considered to be the result of Joule heating and is overlooked without an appropriate analysis. Our experiment and analysis indicate that the heating mechanism is due to the dielectric loss (Debye relaxation). A temperature increase between interdigitated electrodes (IDEs) has been measured with an integrated micro temperature sensor between IDEs to be as high as 70 °C at 1.5 MHz with a 30 Vpp applied voltage to our ultra-low thermal mass DEP device. Analytical and numerical analysis of the power dissipation due to the dielectric loss are in good agreement with the experiment data

Particle entrapment as a feedback effect

We consider a suspension of polarizable particles under the action of traveling wave dielectrophoresis (DEP) and focus on particle induced effects. In a situation where the particles are driven by the DEP force, but no external forces are exerted on the fluid, the joint motion of the particles can induce a steady fluid flow, which leads to particle entrapment. This feedback effect is proven to be non-negligible even for small volume concentration of particles.Comment: 4 pages, 4 figures, submitte