Bacteriophage M13 Aggregation on a Microhole Poly(ethylene-terephthalate) Substrate Produces an Anionic Current Rectifier: Sensitivity toward Anionic versus Cationic Guests

Bacteriophage material (M13, wild-type) deposited as a film onto a poly-ethylene-terephthalate (PET) substrate (6 m thick with a 20 m diameter laser-drilled microhole) has been investigated for ion conductivity and ionic current rectification effects for potential applications in membranes. The M13 aggregate membrane forms under acidic conditions (in aqueous 10 mM acids) and behaves like a microporous anion conductor with micropores defined by the packing of cylindrical virus particles. Asymmetric deposition on the PET film substrate in conjunction with semi-permeability leads to anionic diode behaviour. Typical rectification ratio values are around 10 (determined at +/-1V) in aqueous 10 mM acids. Cationic guest species (aqueous Cu2+, Co2+, Ag+) consistently lead to a rectification minimum at 0.5 mM guest concentration. In contrast, anionic guest species (indigo carmine) lead to a similar rectification minimum already at 5 M concentration. The behaviour is proposed to be associated with cation exclusion effects on transport.