Determining Membrane Capacitance by Dynamic Control of Droplet Interface Bilayer Area

Abstract

By making dynamic changes to the area of a droplet interface bilayer (DIB), we are able to measure the specific capacitance of lipid bilayers with improved accuracy and precision over existing methods. The dependence of membrane specific capacitance on the chain-length of the alkane oil present in the bilayer is similar to that observed in black lipid membranes. In contrast to conventional artificial bilayers, DIBs are not confined by an aperture, which enables us to determine that the dependence of whole bilayer capacitance on applied potential is predominantly a result of a spontaneous increase in bilayer area. This area change arises from the creation of new bilayer at the three phase interface and is driven by changes in surface tension with applied potential that can be described by the Young-Lippmann equation. By accounting for this area change, we are able to determine the proportion of the capacitance dependence that arises from a change in specific capacitance with applied potential. This method provides a new tool with which to investigate the vertical compression of the bilayer and understand the changes in bilayer thickness with applied potential. We find that, for 1,2-diphytanoyl-sn-glycero-3-phosphocholine membranes in hexadecane, specific bilayer capacitance varies by 0.6-1.5% over an applied potential of ±100 mV.

Stable Free-Standing Lipid Bilayer Membranes in Norland Optical Adhesive 81 Microchannels

“…Since the maximum surface area for the lipid bilayer is the size of the aperture (100 m X 85 m), we obtain a specific membrane capacitance of at least 0.4 µF.cm -2 . Considering the lipid bilayer surface area measured with confocal microscopy, we estimate a specific membrane capacitance of ~ 0.5 µF.cm -2 , which is within capacitance values previously reported for DPhPC lipid membranes [29][30][31] , indicating little or no residual decane in the bilayer membrane, and remarkably less than for a bilayer at a droplet interface 30 .…”

The interactions of squalene, alkanes and other mineral oils with model membranes; effects on membrane heterogeneity and function

“…A variety of oils have been used during the generation of DIBs including different alkanes [3,4,12,13], mineral oil [14], squalene [3] and soybean oil [15] and whilst the propensity of some of this oil to remain within the bilayer has been demonstrated previously, the extent and consequences of these interactions has not been fully elucidated and appear to be dependent upon the specific oil used within the protocol. In one case, for example, it was calculated that 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) DIBs would contain 9.2% hexadecane (used in many DIB preparation protocols [3,12]) or 38% decane by volume [16]. This is in comparison to DIBs formed in cis-9-tricosene which produced a lipid bilayer which was essentially solvent-free [16].…”

Formation of lipid bilayer membrane in a poly(dimethylsiloxane) microchip integrated with a stacked polycarbonate membrane support and an on-site nanoinjector

“…The output voltage of the amplifier is monitored with an analog/digital storage oscilloscope (LT342, LeCroy, Chestnut Ridge, NY, USA), digitized via a multimeter (2010, Keithley, Cleveland, OH, USA), and stored on a PC using a LabView program (National Instruments, Austin, TX, USA). Bilayer capacitance is determined by applying a triangular wave 28 (50 mV amplitude and 5 Hz frequency), using a potentiostat (FAS2/Femtostat, Gamry Instruments, Warminster, PA, USA) set at an acquisition frequency of 2 kHz.…”