High Resolution Piezoresponse Force Microscopy Study of Self-Assembled Peptide Nanotubes
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High Resolution Piezoresponse Force Microscopy Study of Self-Assembled Peptide Nanotubes Maxim Ivanov1,2, Ohheum Bak3, Svitlana Kopyll, Semen Vasilev4, Pavel Zelenovskiy4, Vladimir Shur4, Alexei Gruverman3, Andrei Kholkin1,4 1
Department of Physics & CICECO – Aveiro Institute of Materials, University of Aveiro, Aveiro, 3810-193 Portugal 2 Moscow Technological University MIREA, Moscow, 119454, Russian Federation 3 Department of Physics and Astronomy, University of Nebraska - Lincoln, NE 68588, United States 4 School of Natural Sciences and Mathematics, Ural Federal University, Ekaterinburg, 620026, Russian Federation ABSTRACT Peptide nanotubes based on short dipeptide diphenylalanine (FF) attract a lot of attention due to their unique physical properties ranging from strong piezoelectricity to extraordinary mechanical rigidity. In this work, we present the results of high-resolution Piezoresponse Force Microscopy (PFM) measurements in FF microtubes prepared from the solution. First in-situ temperature measurements show that the effective shear piezoelectric coefficient d15 (proportional to axial polarization) significantly decreases (to about half of the initial value) under heating up to 100 o C. The piezoresponse becomes inhomogeneous over the surface being higher in the center of the tubes. Further, PFM study of a composite consisting of FF microtubes and reduced graphene oxide (rGO) was performed. We show that piezoelectric properties of peptide microtubes are significantly modified and radial (vertical) piezoresponse appears in the presence of rGO as confirmed via PFM analysis. The results are rationalized in terms of molecular approach in which π – π molecular interaction between rGO and dipeptide is responsible for the appearance of radial component of polarization in such hybrid structures. INTRODUCTION Recently, short aromatic peptides have attracted significant interest because they can spontaneously form fascinating discrete and well-ordered structures at the nanoscale: nanotubes, nanospheres, nanofibrils, and hydrogels. Peptide nanotubes (PNTs) based on diphenylalanine (FF) possess unique biological and physical properties such as inherent biocompatibility, high aspect ratio and remarkably rigid structure. Strong piezoelectricity found recently in aromatic PNTs [1] adds a new important functionality useful for the development of sensors, actuators and micromechanical systems. Piezoeffect was found to be weakly dependent on frequency and applied electric field, however its temperature dependence was measured either after cooling [2] or by scanning of a small area [3]. Higher chemical reactivity of PNTs as compared to carbon nanotubes (CNTs) or silicon nanowires makes easier to modify their properties with receptor molecules, and more versatile synthesis protocols, whereby a lot of novel devices can be produced [4,5]. Thus, biocompatible, lightweight and highly mechanically stable PNTs are an attractive material for the fabrication of piezoelectric transducers for future generation of chemical sensors and
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