Mild Electric Field Research Articles

Pulsed electric field-assisted extraction of carotenoids from Chlorella zofingiensis

The present work aimed to evaluate the use of PEF as a pretreatment to carotenoid and chlorophyll extraction from two different C. zofingiensis biomasses, green (non-stressed) and orange (stressed). PEF treatment was performed by varying the electric field strength (15, 20, 25 kV/cm) and the treatment time (30, 75, 150 μs). The effect of incubation in a pH 7 buffer for 24 h after PEF and before extraction was also evaluated. The application of an intermediate intensity combined with higher number of pulses (20 kV/cm with 50 pulses) was sufficient to promote the extraction, yielding the highest contents of carotenoids and chlorophylls. The incubation promoted higher extraction yields for treatments performed with shorter treatment times and with mild electric field strengths. Overall, the findings of this study suggest that the application of PEF combined with ethanol could represent a suitable approach for the extraction of carotenoids and chlorophylls from Chlorella zofingiensis biomass.

Influence of mild electric field (MEF) on polyphenol oxidase and quality attributes of pineapple juice during ohmic heating

Fresh pineapple juice was ohmically heated up to 80 ± 2 °C (held for 1 min), followed by cooling. The voltage gradient (VG) of 16 V/cm was kept constant for the come-up period to maintain an identical thermal history. The effect of VG on Polyphenoloxidase (PPO), color, hydroxymethylfurfural (HMF), and total phenolic content (TPC) was evaluated by maintaining 16–36 V/cm at the temperature (80 ± 2 °C). The PPO activity was reduced to 50.06 and 56.67% by hot water (HWT) and ohmic heating (OH) (16 V/cm) treatment, respectively. PPO inactivation showed exponential (k = −0.342; R2 = 0.965) relationship with the VG (16–36 V/cm). The a* value (redness) increased with the VG, whereas the b* (blue-yellow) and hue value remained unchanged up to 16-32V/cm. Both OH and HWT treatments caused an increase in HMF content from 0.145 to 0.351 and 0.233 mg/100 mL, respectively. The TPC content reduced by 18% in HWT, while only 7–10% losses were observed in OH within 16–24 V/cm. The development of HMF with VG was best expressed by the polynomial model (R2 = 0.976–0.994), whereas the TPC degradation followed quadratic relation (R2 = 0.856 ± 0.906). Therefore, it was observed that VG plays an important role in OH-based enzyme inactivation method for pineapple juice.

C. elegans electrotaxis behavior is modulated by heat shock response and unfolded protein response signaling pathways

The nematode C. elegans is a leading model to investigate the mechanisms of stress-induced behavioral changes coupled with biochemical mechanisms. Our group has previously characterized C. elegans behavior using a microfluidic-based electrotaxis device, and showed that worms display directional motion in the presence of a mild electric field. In this study, we describe the effects of various forms of genetic and environmental stress on the electrotactic movement of animals. Using exposure to chemicals, such as paraquat and tunicamycin, as well as mitochondrial and endoplasmic reticulum (ER) unfolded protein response (UPR) mutants, we demonstrate that chronic stress causes abnormal movement. Additionally, we report that pqe-1 (human RNA exonuclease 1 homolog) is necessary for the maintenance of multiple stress response signaling and electrotaxis behavior of animals. Further, exposure of C. elegans to several environmental stress-inducing conditions revealed that while chronic heat and dietary restriction caused electrotaxis speed deficits due to prolonged stress, daily exercise had a beneficial effect on the animals, likely due to improved muscle health and transient activation of UPR. Overall, these data demonstrate that the electrotaxis behavior of worms is susceptible to cytosolic, mitochondrial, and ER stress, and that multiple stress response pathways contribute to its preservation in the face of stressful stimuli.

Formation of magic gold fingers under mild and relevant experimental conditions

Using electrochemical scanning tunneling microscopy (EC-STM) at room temperature and under a liquid layer, magic gold fingers were grown in the presence of three different amino acids, N-Boc-L-Isoleucine, L-Tyrosine, and L-Phenylalanine. The surface was modified using a very mild electric field induced by the tip and the interaction of amino acid molecules with the Au(111) surface. When 0.28 V vs Ag/AgCl was supplied to the working electrode, an extremely small tunneling current of 0.07 nA and a bias of −0.1 V could be used to induce the surface modification. It is clear that a combination of the interaction of the molecules with the surface and the external potential led to the formation of the fingers. The results demonstrate the first instance of this surface structure formed at such mild electric field conditions and imaged under relevant experimental parameters, i.e. at room temperature and in a fluid cell.

Biological effects in photodynamic treatment combined with electropermeabilization in wild and drug resistant breast cancer cells

Electrochemotherapy became one of the therapeutic protocols successfully used in oncology. However, biological effects occurring in cells, especially those which are drug resistant, have not been studied thoroughly. This study presents response of wild and drug resistant breast cancer cells to classical photodynamic therapy with Photofrin or experimental photodynamic therapy with cyanine IR-775, combined with electroporation.Photodynamic reaction or electroporation alone had no cytotoxic effect, but their combination significantly disturbed cellular functions. Applying electroporation allowed the drugs to increase its accumulation, especially for a poorly permeant cyanine in drug resistant cells. FACS analysis showed that even at relatively mild electric field, ca. 90% of cells were permeabilized. High intracellular concentration of drugs triggered the cellular defense system through increased expression of glutathione S-transferase and multidrug resistance proteins (MDR1 and MRP7), particularly in drug resistant cells. Finally, expressively decreased cell metabolism and proliferation, as well as formation of apoptotic bodies and fragmentation of cells were observed after the combined treatment.The results show that electroporation can be used for effective delivery of photosensitizers, even to drug resistant breast cancer cells, which was not tested before. This shows that electro-photodynamic treatment could be a promising approach to overcome a problem of drug resistance in cancer cells.

Bilayer molecular assembly at a solid/liquid interface as triggered by a mild electric field.

The construction of a spatially defined assembly of molecular building blocks, especially in the vertical direction, presents a great challenge for surface molecular engineering. Herein, we demonstrate that an electric field applied between an STM tip and a substrate triggered the formation of a bilayer structure at the solid-liquid interface. In contrast to the typical high electric-field strength (10(9) V m(-1) ) used to induce structural transitions in supramolecular assemblies, a mild electric field (10(5) V m(-1) ) triggered the formation of a bilayer structure of a polar molecule on top of a nanoporous network of trimesic acid on graphite. The bilayer structure was transformed into a monolayer kagome structure by changing the polarity of the electric field. This tailored formation and large-scale phase transformation of a molecular assembly in the perpendicular dimension by a mild electric field opens perspectives for the manipulation of surface molecular nanoarchitectures.

Bilayer Molecular Assembly at a Solid/Liquid Interface as Triggered by a Mild Electric Field

AbstractThe construction of a spatially defined assembly of molecular building blocks, especially in the vertical direction, presents a great challenge for surface molecular engineering. Herein, we demonstrate that an electric field applied between an STM tip and a substrate triggered the formation of a bilayer structure at the solid–liquid interface. In contrast to the typical high electric‐field strength (109 V m−1) used to induce structural transitions in supramolecular assemblies, a mild electric field (105 V m−1) triggered the formation of a bilayer structure of a polar molecule on top of a nanoporous network of trimesic acid on graphite. The bilayer structure was transformed into a monolayer kagome structure by changing the polarity of the electric field. This tailored formation and large‐scale phase transformation of a molecular assembly in the perpendicular dimension by a mild electric field opens perspectives for the manipulation of surface molecular nanoarchitectures.

Overlapping of the Diffuse Double Layer in the Vicinity of the Microporous Electrode

Introduction A microporous electrode with nm-sized micropores on the surface is an attractive subject in electrochemistry. Some experimental results show the physicochemical properties of microporous electrodes are not explained only in terms of the surface area. We have an interest in the electrical double layer in the narrow space. When the size of the micropore on the electrode is smaller than the diffuse part of the electrical double layer, the diffuse double layer show overlap across the pore. This overlapping of the diffuse double layer cannot be estimated on the one dimension model, such as Gouy–Chapman (GC) theory for planar electrodes. We propose a model of the diffuse double layers in the vicinity of micropores on the basis of the Poisson-Boltzmann equation without any complicated assumptions. This calculation shows essential features of the diffuse double layer on the electrode with micropores. The size dependence, the permittivity dependence, the potential dependence, and the electrolyte concentration dependence of the diffuse double layer and also the differential capacitance of the electrode with micropores are discussed.Model The model is described with a cylindrical coordinate. The electrode was assumed as a conductor with an equipotential surface. The diameter of a pore on the electrode was varied from 0.2 to 5 nm. To avoid singular points in the calculation, the radius of the corners was assumed to be 50 pm in the geometry of this model. The solution phase contains a 1:1 electrolyte. In the solution phase, the Poisson–Boltzmann equation was applied to obtain the profile of the electric potential. In this calculation, the relative permittivity was set to be from 10 to 78. The nonlinear Poisson–Boltzmann equation was numerically solved by the finite element method. The differential capacitance of the double layer was estimated from the dependence of the total charge on the electrode surface on the surface potential.Results and discussion The calculated potential profile showed the overlapping of the diffuse double layer in the micropore. The electric field in the micropore is weaker than that outside of the micropore, that is, the overlapped diffuse double layer provides the mild electric field. Assuming that the thickness of the diffuse double layer is the division of the surface potential by the gradient of the potential at the electrode surface, the degree of the overlapping can express qualitatively. When the size of the micropore on the electrode is smaller than the thickness of the diffuse double layer, the calculated capacitance agrees with the GC capacitance at the planner electrode. On the other hand, when the size of the micropore on the electrode is larger than the thickness of the diffuse double layer, the double layer capacitance converges on the GC capacitance at the microporous electrode. This means that the surface area of micropore becomes effective only at thinner diffuse double layers. The change of the thickness of the diffuse double layer in the micropore causes the strong dependence of the capacitance on the potential and the electrolyte concentration compared with the situation of planar electrode. The characteristic features of microporous electrodes would be originated from the heterogeneous electric field caused by the overlapping of the diffuse double layer.

Numerical simulation of diffuse double layer around microporous electrodes based on the Poisson–Boltzmann equation

The structure of the diffuse double layer around a nm-sized micropore on porous electrodes has been studied by numerical simulation using the Poisson–Boltzmann equation. The double layer capacitance of the microporous electrode strongly depends on the electrode potential, the electrolyte concentration, and the size of the micropore. The potential and the electrolyte concentration dependence of the capacitance is different from that of the planner electrode based on the Gouy's theory. The overlapping of the diffuse double layer becomes conspicuous in the micropore. The overlapped diffuse double layer provides the mild electric field. The intensified electric field exists at the rim of the orifice of the micropore because of the expansion of the diffuse double layers. The characteristic features of microporous electrodes are caused by the heterogeneity of the electric field around the micropores.

SEEING AND COMMUNICATING THROUGH WEAK ELECTRIC FIELDS

![][1] Weakly electric fish spend their lives bathed in their own internally generated mild electric field, interpreting perturbations in the field as objects pass through and when communicating with members of their own species through high frequency electric ‘chirps’. Rudiger

Activation of caspases and apoptosis in response to low-voltage electric pulses

Few studies have examined apoptosis induced by low-voltage electric pulses (LVEPs). LVEP-induce changes in membrane potential that are below the membrane breakdown threshold and increase membrane permeability without electroporation (pore formation) through the transport of extracellular substances via phagocytosis. We demonstrated that propidium iodide uptake and apoptosis increased in accordance with the duration and number of LVEPs in B16 cells, which showed relatively good viability under mild electric field conditions. We showed that LVEP-induced apoptosis was achieved through caspase-8 and -9 activation and subsequent caspase-3 activation. Long-duration LVEPs caused only mild cell damage, such that the apoptosis ratio (apoptosis/total cell death) in electric pulse-treated cells was similar to that in non-treated control cells. To assess the relative degree of caspase dependency in LVEP-induced apoptosis, the apoptosis rate and caspase-3 activity were analyzed using a pan-caspase inhibitor (Z-VAD-FMK). Z-VAD-FMK treatment inhibited, but did not abolish, LVEP-induced apoptosis, indicating that caspases other than caspase-3 participate in this pathway. Moreover, LVEP treatment inhibited cell growth, suggesting that LVEP treatment may be a valuable anticancer therapy. Although the mechanism of LVEP-induced apoptosis remains unclear, it may be related to dysfunctional membrane transport of Ca2+ and other extracellular substances involved in caspase activation.