Mohamed M. Sadik

Quantification of propidium iodide delivery using millisecond electric pulses: Experiments

The transport mechanisms in electroporation-mediated molecular delivery are experimentally investigated and quantified. In particular, the uptake of propidium iodide (PI) into single 3T3 fibroblasts is investigated with time- and space-resolved fluorescence microscopy, and as a function of extracellular buffer conductivity. During the pulse, both the peak and the total integrated fluorescence intensity exhibit an inverse correlation with extracellular conductivity. This behavior can be explained by an electrokinetic phenomenon known as Field-Amplified Sample Stacking (FASS). Furthermore, the respective contributions from electrophoresis and diffusion have been quantified; the former is shown to be consistently higher than the latter for the experimental conditions considered. The results are compared with a compact model to predict electrophoresis-mediated transport, and good agreement is found between the two. The combination of the experimental and modeling efforts provides an effective means for the quantitative diagnosis of electroporation.

Quantifying the Effects of Extracellular Conductivity on Transport During Electroporation

Electroporation is an effective means to permeabilize the cell membrane and deliver biologically active molecules (such DNA, RNA, dyes, etc…) into the cell cytoplasm, while maintaining cell viability and functionality [1]. Despite extensive research, electroporation still suffers from major drawbacks such as high cell death and low delivery efficiency. In the past, studies focused mainly on permeabilization of the membrane during electroporation while transport of molecules from one side of the membrane to the other has been overlooked. Previous experimental work demonstrated an inverse relation between the electrical conductivity of the extracellular buffer and total concentration delivered into cells [2]. This inverse correlation suggests that additional molecular transport mechanisms, besides diffusion, govern the delivery into cells.Copyright

Extreme Elongation of Vesicles Under DC Electric Fields

Electrodeformation refers to the deformation of cell or vesicle lipid membranes under the application of an electric field. Such a phenomenon often accompanies electroporation processes, and also can be leveraged to detect pathological changes in cells. Recent studies have suggested that the electrical conductivity difference across the lipid membrane is a dominant factor in determining the characteristics of deformation, and various regimes of deformation were observed. Using a vesicle model system, the current work is the first report of extreme elongation of vesicles of high conductivity ratio under DC electric fields. The results suggest that the osmolarity difference between the encapsulated and bathing solutions may contribute to such abnormal deformation behavior.Copyright