Metal doped polyaniline as neuromorphic circuit elements for in-materia computing.

Polyaniline-based atomic switches are material building blocks whose nanoscale structure and resultant neuromorphic character provide a new physical substrate for the development next-generation, nanoarchitectonic-enabled computing systems. Metal ion-doped devices consisting of a Ag/metal ion doped polyaniline/Pt sandwich structure were fabricated using an in situ wet process. The devices exhibited repeatable resistive switching between high (ON) and low (OFF) conductance states in both Ag+ and Cu2+ ion-doped devices. The threshold voltage for switching was>0.8 V and average ON/OFF conductance ratios (30 cycles for 3 samples) were 13 and 16 for Ag+ and Cu2+ devices, respectively. The ON state duration was determined by the decay to an OFF state after pulsed voltages of differing amplitude and frequency. The switching behaviour is analagous to short-term (STM) and long-term (LTM) memories of biological synapses. Memristive behaviour and evidence of quantized conductance were also observed and interpreted in terms of metal filament formation bridging the metal doped polymer layer. The successful realization of these properties within physical material systems indicate polyaniline frameworks as suitable neuromorphic substrates for in materia computing.

Preparation of poly(epsilon-lysine) adsorbents and application to selective removal of lipopolysaccharides.

To remove endotoxins (lipopolysaccharides; LPS) from cell products used as drugs, water-insoluble poly(epsilon-lysine) (PL) particles were prepared by cross-linking with PL originating from Streptomyces albulus and chloromethyloxirane (CMO). The apparent pKa (pK(a,app)) and the anion-exchange capacity of the particles were easily adjusted by changing the PL ratio and the CMO ratio. The higher the pK(a,app), the greater the LPS-adsorption capacity of the particles. On the other hand, when the PL ratio (in the particles) increased to 75 unit-mol% or higher, the adsorption of bovine serum albumin by the particles also increased, but decreased with increasing ionic strength of the buffer to mu = 0.2 or higher. The adsorption of gamma-globulin increased with decreasing PL ratio to 65 unit-mol% or lower. As a result, when the PL ratio was 70 unit-mol% and the pK(a,app) was 6.7, the PL/CMO particles selectively removed LPS from various protein solutions that were naturally contaminated with LPS, at pH 6.0 and mu = 0.05.