Electrochemical Analysis of Ion Channels and Transporters in Pore-Suspending Membranes - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 315

Whilst the conductance of the bilayer was varied between
G p = 10 -12 S and 5·10 -4 S, the electrolyte conductance was kept
constant at G el = 10 -3 S. The resulting theoretical photocurrent
curves are displayed in Fig. 17 B . In contrast to the photocurrent
that was simulated assuming model A, the initial current after
switching the light source on does not decay in a transient fashion
but is constant at a certain value. This value is nearly preserved
even if the bilayer conductance increased by seven orders of mag-
nitude. Only if G p is increased to 5·10 -4 S, the photocurrent drops
significantly and reaches the regime of the electrolyte resistance.
Variations in C p do not change the course of the photocurrent.
Therefore, the bR-doped pore-spanning bilayer solely acts as an
insulator to enable the detection of an electrical signal between
two electrolyte-filled measuring chambers.

2. Attachment of Purple Membranes to Nano-BLMs

( i ) Functionality of bR in PM-fragments adsorbed on nano-

BLMs

Purple membranes have been adsorbed on many substrates in
order to investigate the light-induced photocurrent generated by
bR. Substrates include membranes like BLMs 94-96 and SSMs 97,98
immobilized on inorganic, conducting materials such as gold 99 or
tin-oxide. Especially BLMs and SSMs are well-suited for the in-
vestigation of electrical properties of ion translocating proteins like
bR. However, BLMs suffer from short lifetimes. This problem can
be overcome by using SSMs that exhibit a high long-term stability.
Unfortunately, they do not allow measuring stationary currents due
to the capacitance of the underlying support, which serves as the
electrode. For the purpose of detecting proton transport, nano-
BLMs were chosen as a suitable alternative as they provide a long-
term stable membrane system (Section II) that additionally is ex-
pected to allow for monitoring stationary currents generated by
immobilized bR. In order to prove this notion, PM-fragments were
adsorbed to preformed nano-BLMs. Adsorption was mediated by
the addition of octadecylamine, which renders the nano-BLM posi-
tively charged so that the negatively charged PM can adsorb elec-
trostatically. Illumination of the membrane-covered porous surface