A new approach for the fabrication of microscale lipid bilayers at glass pipets: application to quantitative passive permeation visualization

Abstract

A new method of planar bilayer lipid membrane (BLM) formation is presented that allows stable, solventfree lipid bilayers exhibiting high seal resistances to be formed rapidly, easily and reproducibly. Using these bilayers the passive permeation of a series of carboxylic acids is investigated, to determine quantitatively the trend in permeability with lipophilicity of the acid. BLMs are formed at the tip openings of pulled theta pipets, and the rate of permeation of each carboxylic acid across the bilayer, from 10 within the pipet into the bulk solution is determined. This is achieved through spatially-resolved measurements of the pH change that occurs upon the permeation of the weak acid, visualized using a pHsensitive fluorophore with a confocal laser scanning microscope. The extracted fluorescence profiles are matched to finite element method (FEM) simulations, to allow the associated permeation coefficient for each weak acid to be determined with high accuracy, since this is the only adjustable parameter used to fit 15 the experimental data. For bilayers formed in this way, the weak acids show increasing permeability with lipophilicity. Furthermore, the arrangement allows the effect of a trans-membrane electric field on permeation to be explored. For both propanoic and hexanoic acid it is found that an applied electric field enhances molecular transport, which is attributed to the formation of pores within the membrane.

Micro‐ and Nano‐Technologies for Lipid Bilayer‐Based Ion‐Channel Functional Assays

“…Unwin et al. modified the tip‐dip method to improve the stability of solvent‐free BLMs that were formed at capillary tips . The lipid monolayer covering the capillary tip was formed directly from a lipid solution in chloroform and the tip was then lowered into a solution that contains a phospholipid monolayer at the air/water interface.…”

“…The potential influence on drug partitioning cannot be neglected, as drug potency can be significantly influenced by drug adhesion to the plate surface in some automated microfluidic patch‐clamp systems . Although only limited groups have reported on the use of a combination of microfabricated devices with solvent‐free BLMs, the next trend promises to be shifted towards the formation of solvent‐free BLMs as a platform for functional integration of eukaryotic channels.…”

Microcavity-Supported Lipid Bilayers; Evaluation of Drug–Lipid Membrane Interactions by Electrochemical Impedance and Fluorescence Correlation Spectroscopy

“…Alternative approaches have emerged that assemble membranes supported over pores which can improve fluidity whilst maintaining stability. [24][25][26] We recently reported a microcavity supported lipid bilayer (MSLB) formed from polystyrene sphere templated polydimethylsiloxane (PDMS) 27 for optical measurements and on gold-coated silicon wafers for electrochemical measurements. These platforms, because of their aqueous filled pore underlying the bilayer, combine the fluidity of a liposome with stability and versatility reminiscent of an SLB.…”

Enhanced Temporal Resolution with Ion Channel-Functionalized Sensors Using a Conductance-Based Measurement Protocol

“…This variability is expected, however, because the BLMs exhibited different seal resistances, ranging from 147 GΩ to 284 GΩ; these values are comparable to those reported for BLMs on micron-sized apertures composed of several different substrates. 19,52–54 The differences in seal resistance among the pipettes/BLMs used here do not pose an impediment for sensing IC activity because each sensor must be calibrated prior to use for quantitative measurements. Though, protocols B–E produced larger relative standard deviations (RSDs) than Protocol A, there was no observed correlation between net conductance acquisition time and RSD (Table 1).…”