A new spiral microelectrode assembly for electroporation and impedance measurements of adherent cell monolayers

Detection of Gram-positive and Gram-negative bacteria membrane permeabilization induced by pulsed electric field using electrochemical admittance spectroscopy

Electrochemical impedance or admittance spectroscopy (EIS or EAS) has been widely used for decades, offering a label-free, rapid, real-time, and non-destructive assay for optically opaque and turbid bacterial solutions. However, PEF-induced changes in the bacterial envelope can present challenges in detecting the extent of membrane permeabilization in both Gram-positive and Gram-negative bacteria due to their distinct morphological properties. Here, we used a new approach for detecting bacterial membrane permeabilization induced by PEF using electrochemical admittance spectroscopy (EAS). The metabolic activity results have shown that the larger L. d. bulgaricus bacteria was found to be significantly more resistant to PEF strengths ranging from 4 to 16 kV/cm than the smaller E. coli bacteria at shorter PEF treatment durations (10 × 10 µs pulses). Interestingly, the difference in the increase of the admittance magnitude and a decrease in phase angle between the PEF treatment times of 10 × 10 µs and 10 × 100 µs pulses at different PEF strengths was more pronounced for E. coli bacteria samples. Our results demonstrate that EAS is more effective in comparing the degree of membrane permeabilization of Gram-positive and Gram-negative bacteria when longer PEF treatment durations are applied.

Transepithelial Electrical Impedance Increase Following Porous Substrate Electroporation Enables Label-Free Delivery

Porous substrate electroporation (PSEP) is a promising new method for intracellular delivery, yet fundamentals of PSEP are not well understood, especially the intermediate processes leading to delivery. PSEP is an electrical method, yet the relationship between PSEP and electrical impedance remains underexplored. In this study, a device capable of measuring impedance and performing PSEP is developed and the changes in transepithelial electrical impedance (TEEI) are monitored. These measurements show TEEI increases following PSEP, unlike other electroporation methods. The authors then demonstrate how cell culture conditions and electrical waveforms influence this response. More importantly, TEEI response features are correlated with viability and delivery efficiency, allowing prediction of outcomes without fluorescent cargo, imaging, or image processing. This label-free delivery also allows improved temporal resolution of transient processes following PSEP, which the authors expect will aid PSEP optimization for new cell types and cargos.

Transepithelial Electrical Impedance Increase Following Porous Substrate Electroporation Enables Label-Free Delivery

Porous substrate electroporation (PSEP) is a promising new method for intracellular delivery, yet fundamentals of the PSEP delivery process are not well understood, partly because most PSEP studies rely solely on imaging for evaluating delivery. Although effective, imaging alone limits understanding of intermediate processes leading to delivery. PSEP is an electrical process, so electrical impedance measurements naturally complement imaging for PSEP characterization. In this study, we developed a device capable of measuring impedance and performing PSEP and we monitored changes in transepithelial electrical impedance (TEEI). Our measurements show TEEI increases following PSEP, unlike other electroporation methods. We then demonstrated how cell culture conditions and electrical waveforms influence this response. More importantly, we correlated TEEI response features with viability and delivery efficiency, allowing prediction of outcomes without fluorescent cargo, imaging, or image processing. This label-free delivery also allows improved temporal resolution of transient processes following PSEP, which we expect will aid PSEP optimization for new cell types and cargos.

Effect of Experimental Electrical and Biological Parameters on Gene Transfer by Electroporation: A Systematic Review and Meta-Analysis

The exact mechanisms of nucleic acid (NA) delivery with gene electrotransfer (GET) are still unknown, which represents a limitation for its broader use. Further, not knowing the effects that different experimental electrical and biological parameters have on GET additionally hinders GET optimization, resulting in the majority of research being performed using a trial-and-error approach. To explore the current state of knowledge, we conducted a systematic literature review of GET papers in in vitro conditions and performed meta-analyses of the reported GET efficiency. For now, there is no universal GET strategy that would be appropriate for all experimental aims. Apart from the availability of the required electroporation device and electrodes, the choice of an optimal GET approach depends on parameters such as the electroporation medium; type and origin of cells; and the size, concentration, promoter, and type of the NA to be transfected. Equally important are appropriate controls and the measurement or evaluation of the output pulses to allow a fair and unbiased evaluation of the experimental results. Since many experimental electrical and biological parameters can affect GET, it is important that all used parameters are adequately reported to enable the comparison of results, as well as potentially faster and more efficient experiment planning and optimization.

Delivery of Foreign Materials into Adherent Cells by Gold Nanoparticle-Mediated Photoporation

Delivering extracellular materials into adherent cells presents several challenges. A homemade photoporation platform, mediated by gold nanoparticles (AuNPs), was constructed to find a suitable method for finding all adherent cells in this process with high delivery efficiency. The thermal dynamics of AuNPs could be monitored. Based on this system, 60 nm AuNPs were selected to be attached to cells for optimal photoporation. After irradiating the cells covered with AuNPs using a nanosecond pulse laser, fluorescein isothiocyanate-dextran in the medium were delivered into optoporated adherent HeLa (human cervical cell lines) cells. The delivery efficiency and cell viability of this process were evaluated using a fluorescence microscope and flow cytometry. The experimental results showed that targeting cells using antibodies, laser irradiation from the top of the cell culture well, and reducing the cell medium are important for improving the delivery efficiency. The optimal loading efficiency for adherent HeLa cells was 53.4%.

The Feasibility of a Smart Surgical Probe for Verification of IRE Treatments Using Electrical Impedance Spectroscopy

SIGNIFICANCE

Irreversible electroporation (IRE) is gaining popularity as a focal ablation modality for the treatment of unresectable tumors. One clinical limitation of IRE is the absence of methods for real-time treatment evaluation, namely actively monitoring the dimensions of the induced lesion. This information is critical to ensure a complete treatment and minimize collateral damage to the surrounding healthy tissue.

GOAL

In this study, we are taking advantage of the biophysical properties of living tissues to address this critical demand.

METHODS

Using advanced microfabrication techniques, we have developed an electrical impedance microsensor to collect impedance data along the length of a bipolar IRE probe for treatment verification. For probe characterization and interpretation of the readings, we used potato tuber, which is a suitable platform for IRE experiments without having the complexities of in vivo or ex vivo models. We used the impedance spectra, along with an electrical model of the tissue, to obtain critical parameters such as the conductivity of the tissue before, during, and after completion of treatment. To validate our results, we used a finite element model to simulate the electric field distribution during treatments in each potato.

RESULTS

It is shown that electrical impedance spectroscopy could be used as a technique for treatment verification, and when combined with appropriate FEM modeling can determine the lesion dimensions.

CONCLUSIONS

This technique has the potential to be readily translated for use with other ablation modalities already being used in clinical settings for the treatment of malignancies.