Structure and electrophysical properties of self-organized composite layers based on peptide and silver nanoparticles

Atomic force microscopy, scanning tunnel microscopy, and IR spectroscopy are employed to study composite films formed from dispersions of silver nanoparticles in an aqueous solution of Asp-Glu-Val-Asp-Trp-Phe-Asp peptide on different substrates at room temperature. It is established that pure peptide crystallizes on substrates to yield different structures, the character of which essentially depends on the chemical nature of a substrate, method of its pretreatment, and solution pH. When films are formed from dispersions containing both silver nanoparticles and peptide, globular structures are formed, in which individual nanoparticles are included into a peptide matrix. It is established that, during the reduction of silver ions and stabilization of resulting nanoparticles, peptide bonds are partly ruptured and another isomeric form (cisconfiguration) of peptide molecules is realized in the silver nanoparticle dispersion in its solution. Distributions of the surface potential and local tunnel voltage-current characteristics are measured for the composite layers. The voltage-current characteristics of all examined composite layers are essentially nonlinear. It is established that the charge transfer in the composite and pure peptide layers is carried out via the Poole-Frenkel mechanism and the Schottky overbarrier emission, respectively.