The cell membrane and the membranes of cellular organelles are mostly composed of lipid bilayers that also include protein molecules. Exposing a cell to an electrical field of sufficient strength and duration increases the permeability of the cell membrane. This phenomenon is called electroporation. Electroporation is routinely used today in biomedicine and biotechnology. Experiments show that during electroporation the changes in the membrane – pores occur within the lipid regions of the cell membrane. Artificially created planar lipid bilayers are often used as an approximation of the actual cell membrane in electroporation research.
Planar lipid bilayers are macroscopically defined by their characteristics such as capacitance, thickness, resistance or conductance, and breaking voltage. Each one of these characteristics requires a specific measurement technique. Measurements are mostly based on voltage or current clamping and then analysing the current or voltage responses respectively.
Constructing planar lipid bilayers is time-consuming and technically challenging. After the planar lipid bilayer is constructed we verify its existence by measuring the current when exposing the potential bilayer to a brief 100 µs voltage pulse with an amplitude of 100 mV. If the current is negligibly small, we measure the capacitance with the pulse discharge method and assess the quality of the planar lipid bilayer. Then we can study the planar lipid bilayer in various ways like measuring its resistivity and capacitance in relation to time with impedance-based methods or we can use a voltage signal that increases linearly with time to determine the breaking time and breaking voltage of the planar lipid bilayer. Experiments are time-consuming and can last multiple hours or even span multiple days.
The purpose of this study is to develop an autonomous measuring system that simplifies and automates the procedures of creating planar lipid bilayers and measuring their electrical properties. The end-user of our system is a researcher in a laboratory.
The system is based on a circuit developed by Rok Malič in his bachelor diploma. We added the functionality of automatic planar lipid bilayer construction with the help of two laboratory syringe pumps WPI ALADDIN-1000, which are controlled with UART communication. Furthermore, we standardized the generation of voltage signals for voltage clamping and enabled measuring electrical current and voltage and further analysis of collected data.
We developed a way for the user to control and take advantage of the system with a personal computer and MATLAB, for which we developed a simple user interface following SCPI (Standard Commands for Programmable Instruments) standards.