A reconstructive phase transition has been found and studied in ultrashort di- and tripeptide nanostructures, self-assembled from biomolecules of different compositions and origin such as aromatic, aliphatic, linear, and cyclic (linear FF-diphenylalanine, linear LL-dileucine, FFF-triphenylalanine, and cyclic FF-diphenylalanine). The native linear aromatic FF, FFF and aliphatic LL peptide nanoensembles of various shapes (nanotubes and nanospheres) have asymmetric elementary structure and demonstrate nonlinear optical and piezoelectric effects. At elevated temperature, 140-180 °C, these native supramolecular structures (except for native Cyc-FF nanofibers) undergo an irreversible thermally induced transformation via reassembling into a completely new thermodynamically stable phase having nanowire morphology similar to those of amyloid fibrils. This reconstruction process is followed by deep and similar modification at all levels: macroscopic (morphology), molecular, peptide secondary, and electronic structures. However, original Cyc-FF nanofibers preserve their native physical properties. The self-fabricated supramolecular fibrillar ensembles exhibit the FTIR and CD signatures of new antiparallel β-sheet secondary folding with intermolecular hydrogen bonds and centrosymmetric structure. In this phase, the β-sheet nanofibers, irrespective of their native biomolecular origin, do not reveal nonlinear optical and piezoelectric effects, but do exhibit similar profound modification of optoelectronic properties followed by the appearance of visible (blue and green) photoluminescence (PL), which is not observed in the original peptides and their native nanostructures. The observed visible PL effect, ascribed to hydrogen bonds of thermally induced β-sheet secondary structures, has the same physical origin as that of the fluorescence found recently in amyloid fibrils and can be considered to be an optical signature of β-sheet structures in both biological and bioinspired materials. Such PL centers represent a new class of self-assembled dyes and can be used as intrinsic optical labels in biomedical microscopy as well as for a new generation of novel optoelectronic nanomaterials for emerging nanophotonic applications, such as biolasers, biocompatible markers, and integrated optics.

Bio-nanophotonics is a wide field in which advanced optical materials, biomedicine, fundamental optics, and nanotechnology are combined and result in the development of biomedical optical chips. Silk fibers or synthetic bioabsorbable polymers are the main light-guiding components. In this work, an advanced concept of integrated bio-optics is proposed, which is based on bioinspired peptide optical materials exhibiting wide optical transparency, nonlinear and electrooptical properties, and effective passive and active waveguiding. Developed new technology combining bottom-up controlled deposition of peptide planar wafers of a large area and top-down focus ion beam lithography provides direct fabrication of peptide optical integrated circuits. Finding a deep modification of peptide optical properties by reconformation of biological secondary structure from native phase to β-sheet architecture is followed by the appearance of visible fluorescence and unexpected transition from a native passive optical waveguiding to an active one. Original biocompatibility, switchable regimes of waveguiding, and multifunctional nonlinear optical properties make these new peptide planar optical materials attractive for application in emerging technology of lab-on-biochips, combining biomedical photonic and electronic circuits toward medical diagnosis, light-activated therapy, and health monitoring.

The emerging "bottom-up" nanotechnology reveals a new field of bioinspired nanomaterials composed of chemically synthesized biomolecules. They are formed from elementary constituents in supramolecular structures by the use of a developed nature self-assembly mechanism. The focus of this perspective paper is on intrinsic fundamental physical properties of bioinspired peptide nanostructures and their small building units linked by weak noncovalent bonds. The observed exceptional optical properties indicate a phenomenon of quantum confinement in these supramolecular structures, which originates from nanoscale size of their elementary building blocks. The dimensionality of the confinement gives insight into intrinsic packing of peptide supramolecular nanomaterials. QC regions, revealed in bioinspired nanostructures, were found by us in amyloid fibrils formed from insulin protein. We describe ferroelectric and related properties found at the nanoscale based on original crystalline asymmetry of the nanoscale building blocks, packing these structures. In this context, we reveal a classic solid state physics phenomenon such as reconstructive phase transition observed in bioorganic peptide nanotubes. This irreversible phase transformation leads to drastic reshaping of their quantum structure from quantum dots to quantum wells, which is followed by variation of their space group symmetry from asymmetric to symmetric. We show that the supramolecular origin of these bioinspired nanomaterials provides them a unique chance to be disassembled into elementary building block peptide nanodots of 1-2 nm size possessing unique electronic, optical and ferroelectric properties. These multifunctional nanounits could lead to a new future step in nanotechnology and nanoscale advanced devices in the fields of nanophotonics, nanobiomedicine, nanobiopiezotronics, etc.

Many peptide nanostructures, self-assembled from chemically synthesized biomolecules, have drawn much attention in the fi eld of nanotechnology due to their physical, chemical, and biological properties, which make them promising candidates for applications in bionanomedicine, [ 1 ] bionanotechnology, [ 2,3 ] electronics, [ 4,5 ] optics, [ 6 ] energy storage, [ 7,8 ] etc. Some of these properties, such as ferro-and piezoelectricity observed in diphenylalanine nanotubes (FF-PNT) [ 9 ] are directly related to the nanocrystalline structural asymmetry of the elementary building blocks comprising these supramolecular materials. [ 6,10 ] One basic physical effect that depends on both the crystalline symmetry and the electronic properties of dielectric materials is second harmonic generation (SHG). SHG is observed only in crystals with no center of symmetry [ 11 ] and is related to ferroelectric phenomena together with linear electrooptical and piezoelectric effects. Ferroelectric effects have been observed in many biological materials such as plants, animals, and human tissues (amino acids, pineal gland of brain, skin, tendon, etc.). [ 12 ] Today, the SHG effect is also exploited in optical microscopy, especially in medical and biological research. [ 13 ] It allows the detection of two-photon emission from biomaterials and biopolymers [ 14 ] lacking a center of symmetry. The effect has been used with quantitative metrics for diagnosing a wide range of diseases. [ 15 ] Recently, second-order responses have also been found in bioinspired aromatic FF-PNT with hexagonal space group P6 1 using nonlinear optical microscopy. [ 16 ] Both the elementary crystalline symmetry and the electronic structure of bioinspired peptide nanostructures can be significantly changed by deep reconstruction process, such as phase transformation at a nanoscale level, which results in the disappearance of an SHG response. [ 17 ] Another method to modulate these fundamental properties is to use different solvents, [18][19][20][21] which strongly infl uence the self-assembly process and defi ne peptide nanostructures' morphologies. Modifi cation of the physical properties in peptide nanomaterials is a new way to fabricate basic nanoscale units for future bottom-up nanotechnologies. [ 6 ] Bioinspired peptide nanostructures, much like other organic nanostructures, [ 22,23 ] have ultra-small sizes and are easily produced by a rapid self-assembly fabrication process. All these properties make them favorable for implementation in diverse applications, and especially in biophotonics devices.In this work, we have studied the SHG effect in bioorganic peptide nanostructures of different morphologies and symmetries, such as nanotubes, nanofi bers, nanobelts, and nanospheres. These nanostructures were self-assembled in different solvents from peptide precursors with a variable number of A nonlinear optical effect of a second harmonic generation (SHG) was fi rst observed in quartz and then found in many inorganic materials that have an asymmetric crystalline s...

Thermally induced phase transformation in bioorganic nanotubes, which self-assembled from two ultrashort dipeptides of different origin, aromatic diphenylalanine (FF) and aliphatic dileucine (LL), is studied. In both FF and LL nanotubes, irreversible phase transformation found at 120-180 °C is governed by linear-to-cyclic dipeptide molecular modification followed by formation of extended β-sheet structure. As a result of this process, native open-end FF and LL nanotubes are transformed into ultrathin nanofibrils. Found deep reconstructions at all levels from macroscopic (morphology) and structural space symmetry to molecular give rise to new optical properties in both aromatic FF and aliphatic LL nanofibrils and generation of blue photoluminescence (PL) emission. It is shown that observed blue PL peak is similar in these supramolecular nanofibrillar structures and is excited by the network of non-covalent hydrogen bonds that link newly thermally induced neighboring cyclic dipeptide strands to final extended β-sheet structure of amyloid-like nanofibrils. The observed blue PL peak in short dipeptide nanofibrils is similar to the blue PL peak that was recently found in amyloid fibrils and can be considered as the optical signature of β-sheet structures. Nanotubular structures were characterized by environmental scanning electron microscope, ToF-secondary ion mass spectroscopy, CD and fluorescence spectroscopy.