Novel Langmuir-Blodgett membranes for silicon-based ion sensors

An improved preparation for electrolyte/Langmuir-Blodgett film/oxide/silicon (ELBOS) structures with ultrathin Langmuir-Blodgett (LB) films of substituted phthalocyaninato-polysiloxane (PCPS) polymers is presented. This allows for the assembly of LB films with only 2–20 layers which show no degradation for at least 140 days in permanent contact with liquid electrolytes. The PCPS films are pH sensitive, their sensitivity depending on the number of layers and ranging from 36 mV/pH for 2 layers to 56 mV/pH for 20 layers. The PCPS film is claimed to be a protonic conductor. The pH sensitivity is related to protonic sites at the polymer molecule, leading to an increase in the number of sites with increasing number of layers. New LB films of a poly(γ-methyl-L-glutamate-co-γ-n-octadecyl-L-glutamate) (PG) show a reduced pH sensitivity of less than 13 mV/pH and may serve as a reference element in an all-solid-state LB film ion-sensing device.