Photogating of ionic currents across a lipid bilayer.

Photoformation of metalloporphyrin cations in a lipid bilayer increases the ionic currents of negative and decreases those of positive hydrophobic ions. At low concentrations of the mobile hydrophobic ion, a 30% change in conductivity is observed that decreases with increasing concentration of positive tetraphenylphosphonium ion and increases drastically with increasing concentration of negative tetraphenylboride ion. In the region of saturated conductance of boride ion, the increase in conductivity is 3.6-fold. A 15-fold increase is observed with the protonophore carbonyl cyanide 3-chlorophenylhydrazone. In this case the net charge gated is 300 times greater than the photogenerated charge in the bilayer membrane. Thus there is a net gain in this organic field effect phototransistor. The gating can also be accomplished by continuous light or chemical oxidants. Photogating is explained as space charge effects inside the bilayer.