We report on observation of photoluminescence (PL) in blue and UV regions of exciton origin in bioinspired material-peptide nanotubes (PNTs). Steplike optical absorption and PL measurements have allowed finding quantum confined (QC) phenomenon in PNTs. The estimations show that QC in these nanotubes occurs due to a crystalline structure of subnanometer scale dimension formed under the self-assembly process. Our new findings pave the way for the integration of PNT in a new generation of optical devices. A blue PL array of a PNT-patterned device is demonstrated.

In the world of biology, "self-assembly" is the ability of biological entities to interact with one another to form supramolecular structures. One basic group of self-assembled structures is peptide nanotubes (PNTs). However, the self-assembly mechanism, with its special characteristics, is not yet fully understood. An exceptional quantum-confined approach is shown here for the self-assembly mechanism in bio-inspired materials. We found the elementary building block of the studied PNT, which is self-assembled from short peptides composed of two phenylalanine residues, to be 0D-quantum-confined (can be related to confinement in 3D), also called a quantum dot (QD). This elementary building block can further self-assemble to a PNT formation. It has been observed that the assembly process of dots to tubes and the disassembly process of tubes to dots are reversible. We further show that a similar dipeptide can also self-assemble to a QD-like structure, with different dimensions. The presented peptide QD structures are nanometer-sized structures, with pronounced exciton effects, which may promote the use of an entirely new kind of organic QDs.

The piezoelectric effect has been studied in wet and dry human bones using a piezoresponse force microscope (PFM). It allowed to measure piezoelectric response with nanometer scale resolution directly in a collagen matrix and to obtain a piezoresponse image near the Haversian channel. Dielectric response and dc conductivity have been measured. Theoretical calculations taking into account the inhomogeneity of the electric field under the PFM tip apex and its screening in highly conductive bone samples were performed for obtaining the piezoelectric coefficient in the bone collagen.Ferroelectric phenomena have been observed in many biological materials. The origin of these fundamental physical properties is ascribed to high structural ordering of biological systems at any level that is a low symmetry configuration of elementary cells based of their helical or chiralic dissymmetry. Linear electrooptic effect has been found in nerve fibers. 1 Dielectric spectroscopy studies of oriented purple membranes showed that bacteriorhodopsin, which is an integral membrane protein, possesses a significant electrical dipole moment and demonstrates a liquid crystal-like ferroelectric behavior. 2 This experiment was a direct confirmation of the theoretical model of ion channels in a biological membrane 3,4 acting as electric switches between ferroelectric (closed, insulating) and paraelectric (open, ion-conducting) states. Plants and animal and human tissues (protein amino acids, pineal gland of brain, bones, skin, tendon, etc.) reveal pronounced piezoelectric 5,6 and pyroelectric properties. 7-9 Reports on the observation of pyroelectric effect 7-9 was a first evidence of the existence of macroscopic spontaneous electrical polarization in bones. Application of an ac electric field to the cortical human bone allowed to observe reversal of the spontaneous polarization by recording dielectric hysteresis loop. 10 Both piezoelectric and pyroelectric phenomena were related to collagen, which is an organic crystalline matrix of the bone composed from strongly aligned polar organic protein molecules. 11 It was proposed that the piezoelectric effect plays an important physiological role in bone growth, remodeling, and fracture healing. 12In this paper we report on studies of piezoelectric effect in moist and dry human bones by the use of a piezoresponse force microscope (PFM). It allowed both to measure piezoelectric response with nanometer scale resolution directly in a collagen matrix and to obtain a piezoresponse image near the Haversian channel. Theoretical calculations, taking into account the inhomogeneity of the electric field under the PFM tip apex and screening of the applied electric field, were performed for obtaining the piezoelectric coefficient in bone collagen.Human adult humerus and tibia diaphysial fragments were used for sample preparation. Bones were supplied by The Israeli National Bone Bank at the Chaim Sheba Medical Center. All the bones were obtained from young (<45 years of age) individuals during organ harvesting a...

A theory of an equilibrium shape of domains formed in an electric field of atomic force microscope (AFM) is proposed. The domain shape depends on parameters of the ferroelectric and on the applied voltage. Under low voltages the length and the diameter of the domain are of the same order of magnitude. With voltage increase the ratio between the length and the diameter increases. A correlation between the lateral sizes and the spontaneous polarization value is considered. It is shown that under the same voltage the thinnest domains are formed in ferroelectrics with high spontaneous polarization. The concept of the domain shape invariant as a combination of the domain length and lateral size, which is constant when changing the AFM parameters, is introduced. Results of the calculation of the invariant value in barium titanate as well as of the domain dimensions and the shape in GASH are in good agreement with the experiment.