Bilayer lipid membrane (BLM) based ion selective electrodes at the meso-, micro-, and nano-scales

Abstract

This paper presents a novel method for making micron-sized apertures with tapered sidewalls and nano-sized apertures. Their use in bilayer lipid membrane-based ion selective electrode design is demonstrated and compared to mesoscale bilayers and traditional PVC ion selective electrodes. Micron-sized apertures are fabricated in SU-8 photoresist films and vary in diameter from 10 to 40 microns. The tapered edges in SU-8 films are desired to enhance bilayer lipid membrane (BLM) formation and are fabricated by UV-light overexposure. Nanoapertures are made in boron diffused silicon film. The membranes are used as septa to separate two potassium chloride solutions of different concentrations. Lecithin BLMs are assembled on the apertures by ejecting lipid solution. Potassium ionophore, dibenzo-18-crown-6, is incorporated into BLMs by dissolving it in the lipid solution before membrane assembly. Voltage changes with increasing potassium ion concentrations are recorded with an A/D converter. Various ionophore concentrations in BLMs are investigated. At least a 1% concentration is needed for consistent slopes. Electrode response curves are linear over the 10−6 to 0.1 M range with a sub-Nernstian slope of 20 mV per Log concentration change. This system shows high selectivity to potassium ions over potential interfering sodium ions. BLMs on the three different aperture sizes at the meso, micro, and nano-scales all show similar linear ranges and limits of detection (LODs) as PVC ion selective membranes.

Stable lipid bilayers based on micro- and nano-fabrication

“…suggests that the annulus -septum contact angle should be small for a stable arrangement of BLMs (19,25,26), the tapered aperture edge, as well as nanometre thickness of the septum, is favourable to improve the BLM stability. Formation of free-standing BLMs across the aperture was investigated by the folding method.…”

“…Extensive studies have been made to improve the stability of free-standing BLMs by preparing BLMs in microfabricated devices (3,(8)(9)(10)(11)(12)(13) or supporting BLMs with hydrogels (14)(15)(16)(17). These efforts led to prolonged membrane lifetime of several tens of hours (18,19). However, mechanical stability of the BLMs has not been improved to the desired extent.…”

Stable Lipid Bilayers Based on Micro- and Nano-Fabrication as a Platform for Recording Ion-Channel Activities

“…6,[11][12][13][14][15][16] These efforts have led to a prolonged membrane lifetime of several tens of hours. 12,17 However, the mechanical stability of the BLMs has not been improved to the desired extent. In addition, these approaches are commonly based on BLMs prepared from lipid solutions in unvolatile organic solvents, which are often criticized that some amount of the solvent remains in the central hydrophobic area of the BLMs, 18 and likely denatures ion-channel functions.…”

Emerging trends in precision fabrication of microapertures to support suspended lipid membranes for sensors, sequencing, and beyond

“…Liu et al described the fabrication of nanoapertures in a silicon oxide/boride thin film by electron beam lithography [24]. In this procedure, boron diffusion is used to form a thin boride layer at the surface of a silicon wafer.…”