Biomedical Engineering Reference
In-Depth Information
by impedance spectroscopy and, in part, voltage clamp experi-
ments on single ion channel forming peptides and proteins.
II. ELECTROCHEMICAL CHARACTERISATION OF
PORE-SUSPENDING MEMBRANES
1. Nano-BLMs
A couple of years ago, we developed an artificial membrane sys-
tem based on porous alumina substrates that can be considered as a
hybrid between a solid supported membrane and a freestanding
lipid bilayer. As each of the bilayers spanning the pores of the sub-
strate resembles a black lipid membrane (BLM), a membrane that
was first invented by Müller and Rudin in the 1970's, but of nano-
metre size, the system was called nano-BLMs.
To investigate the electrical properties, such as capacitance
and resistance of lipid membranes, electrochemical impedance
spectroscopy (EIS) is a powerful technique.
12,20,21
In general, this
method is well suited to elucidate the electrochemical properties of
sensitive biological interfaces in a non-invasive manner by the ap-
plication of an alternating voltage of small amplitude.
(
i
)
Formation and Impedance Analysis of Nano-BLMs
Porous alumina can be prepared easily, reproducibly and ra-
ther cheaply in almost arbitrary lateral dimensions, making this
material well suited for routine applications as well as for biosen-
sor devices. The substrates are formed by anodisation in the pres-
ence of acids.
22,23
To use them as an underlying substrate for nano-
BLMs, the pore-bottoms need to be removed, which results in a
sieve-like structure.
24
For the formation of nano-BLMs we adapted
a method, which was originally established to prepare solid sup-
ported membranes on gold electrodes.
9
The strategy is to utilize
the strong, quasi-covalent interaction between gold and sulfur to
chemisorb alkane thiols or thiol-functionalized lipids such as the
phospholipid 1,2-dipalmitoyl-
sn
-glycero-3-phosphothioethanol
(DPPTE) on gold surfaces. Thus, the upper part of the alumina
substrates is covered with a 60 nm gold layer followed by the
chemisorption of a thiol compound that renders the upper surface
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