The structure, morphology and electrical properties of thin dipeptide hexamethylenediamide bis (N-monosuccinylglutamlysin) (DPT) layers and a DPT composite with gold nanoparticles deposited on gold and HOPG substrates were studied by probe microscopy and spectroscopy. The chemical formula of DPT is: {HOOC–(CH2)2–CO-L-Glu-L-Lys-NH–(CH2)3}2, and it is a mimetic of nerve growth factor. The results demonstrate that the structure and morphology of DPT thin layers depend significantly on the molecule charge (neutral or anion) and the nature of the substrate–layer interface. It was possible to control the structure and properties of the formed solid layers by changing pH of aqua solution (the charge of the DPT molecule). Bipolar resistive switching was observed in thin DPT layers on graphite and gold surfaces. The crystallization of anions on the surface of gold led to the formation of a ferroelectric unlike graphite. A strong dependence of the morphology of DPT composite layers on the nature of the substrate and the state of its surface is revealed. It indicates the important role of interfacial interactions in the crystallization processes of the DPT layers. The electrical properties of layers also depend on the interaction of DPT with the substrate. An increase in the thickness of the layers significantly affects the morphology and value of the tunneling current. Similar to crystallization of DPT salt on a gold surface, crystallization of DPT composite with gold nanoparticles also leads to the formation of a ferroelectric. The differences found in the structure of DPT composite layers on graphite and gold surfaces can be explained by assuming that the structure of the second and all subsequent layers is completely determined by the structure of the first adsorption layer in DPT-substrate interface. So this layer serves as a template for the growth of all other layers. The results can find practical application in 3D printing technologies. The presence of negative differential conductivity on local tunnel current–voltage characteristics of peptide composites is of great practical importance when used as active elements for amplifying current and power, memory cells in organic electronics. Investigated DPT has rather good memristive characteristics, including good endurance, satisfying ON/OFF current ratio, long retention time and reproducible write-once read-many times (WORM) memory behavior. All this allows us to consider the DPT to be a perspective material of memristor organic electronics. Since it is also a drug, the polymorphism and its dependence on pH can also find application in the pharmaceutical industry.
Bio-Memristor Based on Peptide and Peptide Composite with Gold Nanoparticles