Improvement of Background Solution for Optically Induced Dielectrophoresis-Based Cell Manipulation in a Microfluidic System

Optically induced dielectrophoresis (ODEP) is effective for cell manipulation. However, its utilization has been limited by the requirement of solution with low conductivity. This issue has been ignored in ODEP-relevant studies. To address this issue, this study aims to investigate to what extent the cell viability and performance of ODEP-based cell manipulation are affected by low conductivity conditions. Additionally, this study aims to modify sucrose solutions to reduce the impacts caused by low-conductivity solutions. Results revealed the use of sucrose solution in ODEP operation could significantly reduce the viability of the manipulated cells by 9.1 and 38.5% after 2- and 4-h incubation, respectively. Prolonged operation time (e.g., 4 h) in sucrose solution could lead to significantly inferior performance of cell manipulation, including 47.2% reduction of ODEP manipulation velocity and 44.4% loss of the cells manipulatable by ODEP. The key finding of this study is that the use of bovine serum albumin (BSA)-supplemented sucrose solution (conductivity: 25–50 μS cm−1) might significantly increase the cell viability by 10.9–14.8% compared with that in sucrose solution after 4 h incubation. Moreover, the ODEP manipulation velocity of cells in the BSA-supplemented sucrose solution (conductivity: 25 μS cm−1) was comparable to that in sucrose solution during 4-h incubation. More importantly, compared with sucrose solution, the use of BSA-supplemented sucrose solution (conductivity: 25–50 μS cm−1) contributed high percentage (80.4–93.5%) of the cells manipulatable by ODEP during 4-h incubation. Overall, this study has provided some fundamental information relevant to the improvement of background solutions for ODEP-based cell manipulation.

Dielectric Properties of Phosphatidylcholine Membranes and the Effect of Sugars

Simple carbohydrates are associated with the enhanced risk of cardiovascular disease and adverse changes in lipoproteins in the organism. Conversely, sugars are known to exert a stabilizing effect on biological membranes, and this effect is widely exploited in medicine and industry for cryopreservation of tissues and materials. In view of elucidating molecular mechanisms involved in the interaction of mono- and disaccharides with biomimetic lipid systems, we study the alteration of dielectric properties, the degree of hydration, and the rotational order parameter and dipole potential of lipid bilayers in the presence of sugars. Frequency-dependent deformation of cell-size unilamellar lipid vesicles in alternating electric fields and fast Fourier transform electrochemical impedance spectroscopy are applied to measure the specific capacitance of phosphatidylcholine lipid bilayers in sucrose, glucose and fructose aqueous solutions. Alteration of membrane specific capacitance is reported in sucrose solutions, while preservation of membrane dielectric properties is established in the presence of glucose and fructose. We address the effect of sugars on the hydration and the rotational order parameter for 1-palmitoyl-2-oleoyl-sn-glycero-3- phosphocholine (POPC) and 1-stearoyl-2-oleoyl-sn-glycero-3- phosphocholine (SOPC). An increased degree of lipid packing is reported in sucrose solutions. The obtained results provide evidence that some small carbohydrates are able to change membrane dielectric properties, structure, and order related to membrane homeostasis. The reported data are also relevant to future developments based on the response of lipid bilayers to external physical stimuli such as electric fields and temperature changes.

Mechanisms of Viscous Media Effects on Elementary Steps of Bacterial Bioluminescent Reaction

Enzymes activity in a cell is determined by many factors, among which viscosity of the microenvironment plays a significant role. Various cosolvents can imitate intracellular conditions in vitro, allowing to reduce a combination of different regulatory effects. The aim of the study was to analyze the media viscosity effects on the rate constants of the separate stages of the bacterial bioluminescent reaction. Non-steady-state reaction kinetics in glycerol and sucrose solutions was measured by stopped-flow technique and analyzed with a mathematical model developed in accordance with the sequence of reaction stages. Molecular dynamics methods were applied to reveal the effects of cosolvents on luciferase structure. We observed both in glycerol and in sucrose media that the stages of luciferase binding with flavin and aldehyde, in contrast to oxygen, are diffusion-limited. Moreover, unlike glycerol, sucrose solutions enhanced the rate of an electronically excited intermediate formation. The MD simulations showed that, in comparison with sucrose, glycerol molecules could penetrate the active-site gorge, but sucrose solutions caused a conformational change of functionally important αGlu175 of luciferase. Therefore, both cosolvents induce diffusion limitation of substrates binding. However, in sucrose media, increasing enzyme catalytic constant neutralizes viscosity effects. The activating effect of sucrose can be attributed to its exclusion from the catalytic gorge of luciferase and promotion of the formation of the active site structure favorable for the catalysis.

Poor adult nutrition impairs learning and memory in a parasitoid wasp

Animals have evolved cognitive abilities whose impairment can incur dramatic fitness costs. While malnutrition is known to impact brain development and cognitive functions in vertebrates, little is known in insects whose small brain appears particularly vulnerable to environmental stressors. Here, we investigated the influence of diet quality on learning and memory in the parasitoid wasp Venturia canescens. Newly emerged adults were exposed for 24 h to either honey, 20% sucrose solution, 10% sucrose solution, or water, before being conditioned in an olfactory associative learning task in which an odor was associated to a host larvae (reward). Honey fed wasps showed 3.5 times higher learning performances and 1.5 times longer memory retention than wasps fed sucrose solutions or water. Poor diets also reduced longevity and fecundity. Our results demonstrate the importance of early adult nutrition for optimal cognitive function in these parasitoid wasps that must quickly develop long-term olfactory memories for searching suitable hosts for their progeny.

Selective recruitment for pollen and nectar sources in honeybees

Honeybees (Apis mellifera) use cues and signals to recruit nestmates to profitable food sources. Here we investigate whether the type of resource advertised within the colony (i.e., pollen or nectar) correlates with the recruits’ choices at the feeding site. We observed that pollen recruits preferred to collect pollen once arrived for the first time at the feeding site, while nectar recruits preferred to forage sucrose solutions. Bees recruited by foragers carrying both resources show intermediate preferences. Studying the plasticity of this response, we found that nectar recruits have a low probability of switching to pollen collection, yet pollen recruits were likely to switch to sucrose solution of increasing concentrations. Our results show that cues associated with the advertised resource type correlate with recruits foraging tendency for pollen and sucrose solution, a feature that would guarantee an efficient resource collection.

Sucrose solution as a new viscous test fluid with tunable viscosities up to 2 Pas for micromixing characterization by the Villermaux–Dushman reaction

For the first time, micromixing characterization for the Villermaux–Dushman reaction could be performed with a non-reactive viscous medium at viscosities up to 2 Pas. As viscous medium, sucrose solution was used with the benefit of being a Newtonian fluid with tuneable viscosity. Due to the higher viscosities in comparison to established media for micromixing investigations, a new protocol for the experimental implementation was developed. Micromixing experiments were conducted and the applicability of viscous sucrose solutions was proven in a stirred tank reactor. Major challenges in characterizing micromixing efficiency in high viscous solution were consolidated.