Amir Handelman

Reconstructive Phase Transition in Ultrashort Peptide Nanostructures and Induced Visible Photoluminescence

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.

Structural and optical properties of short peptides: nanotubes‐to‐nanofibers phase transformation

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. Copyright

Optical transition induced by molecular transformation in peptide nanostructures

In this letter we present a variation in the optical properties of bio-organic peptide nanostructures, which are induced by molecular transformation. The self-assembled tubular structures are formed from short aromatic di-peptides. Upon thermal induction, the structure changes its molecular conformation, and the linear di-peptide closes into a cyclic peptide. This irreversible transition changes the molecular packing at the nanoscale, which results in reconstruction of the native quantum dot-like packing to quantum well-like packing and the generation of blue luminescence. We further show that the same cyclic peptide can exhibit different photoluminescence properties according to the formed structure.

Linear and nonlinear optical waveguiding in bio-inspired peptide nanotubes.

Unique linear and nonlinear optical properties of bioinspired peptide nanostructures such as wideband transparency and high second-order nonlinear optical response, combined with elongated tubular shape of variable size and rapid self-assembly fabrication process, make them promising for diverse bio-nano-photonic applications. This new generation of nanomaterials of biological origin possess physical properties similar to those of biological structures. Here, we focus on new specific functionality of ultrashort peptide nanotubes to guide light at fundamental and second-harmonic generation (SHG) frequency in horizontal and vertical peptide nanotubes configurations. Conducted simulations and experimental data show that these self-assembled linear and nonlinear optical bio-waveguides provide strong optical power confinement factor, demonstrate pronounced directionality of SHG and high conversion efficiency of SHG ∼10(-5). Our study gives new insight on physics of light propagation in nanostructures of biological origin and opens the avenue towards new and unexpected applications of these waveguiding effects in bio-nanomaterials both for biomedical nonlinear microscopy imaging recognition and development of novel integrated nanophotonic devices.

Bioorganic nanodots for non-volatile memory devices

In recent years we are witnessing an intensive integration of bio-organic nanomaterials in electronic devices. Here we show that the diphenylalanine bio-molecule can self-assemble into tiny peptide nanodots (PNDs) of ∼2 nm size, and can be embedded into metal-oxide-semiconductor devices as charge storage nanounits in non-volatile memory. For that purpose, we first directly observe the crystallinity of a single PND by electron microscopy. We use these nanocrystalline PNDs units for the formation of a dense monolayer on SiO2 surface, and study the electron/hole trapping mechanisms and charge retention ability of the monolayer, followed by fabrication of PND-based memory cell device.

Ferroelectric Properties and Phase Transition in Dipeptide Nanotubes

Small aromatic dipeptides can self-assemble into supramolecular bioinspired peptide nanotubes. Nanoscale dimensions of their nanocrystalline building blocks and their space symmetry is the origin for exceptional physical properties of these nanotubular structures, such as quantum confinement and ferroelectric-related phenomena (piezoelectricity, second harmonic generation and spontaneous polarization). In this work we study basic intrinsic physical properties in diphenylalanine-based peptide nanostructures, and follow their variation during the phase transition process.

Peptide Optical waveguides

Small‐scale optical devices, designed and fabricated onto one dielectric substrate, create integrated optical chip like their microelectronic analogues. These photonic circuits, based on diverse physical phenomena such as light–matter interaction, propagation of electromagnetic waves in a thin dielectric material, nonlinear and electro‐optical effects, allow transmission, distribution, modulation, and processing of optical signals in optical communication systems, chemical and biological sensors, and more. The key component of these optical circuits providing both optical processing and photonic interconnections is light waveguides. Optical confinement and transmitting of the optical waves inside the waveguide material are possible due to the higher refractive index of the waveguides in comparison with their surroundings.

Strong Electro‐Optic Effect and Spontaneous Domain Formation in Self‐Assembled Peptide Structures

Short peptides made from repeating units of phenylalanine self‐assemble into a remarkable variety of micro‐ and nanostructures including tubes, tapes, spheres, and fibrils. These bio‐organic structures are found to possess striking mechanical, electrical, and optical properties, which are rarely seen in organic materials, and are therefore shown useful for diverse applications including regenerative medicine, targeted drug delivery, and biocompatible fluorescent probes. Consequently, finding new optical properties in these materials can significantly advance their practical use, for example, by allowing new ways to visualize, manipulate, and utilize them in new, in vivo, sensing applications. Here, by leveraging a unique electro‐optic phase microscopy technique, combined with traditional structural analysis, it is measured in di‐ and triphenylalanine peptide structures a surprisingly large electro‐optic response of the same order as the best performing inorganic crystals. In addition, spontaneous domain formation is observed in triphenylalanine tapes, and the origin of their electro‐optic activity is unveiled to be related to a porous triclinic structure, with extensive antiparallel beta‐sheet arrangement. The strong electro‐optic response of these porous peptide structures with the capability of hosting guest molecules opens the door to create new biocompatible, environmental friendly functional materials for electro‐optic applications, including biomedical imaging, sensing, and optical manipulation.

Bioinspired Peptide Nanotubes: Ferroelectricity at Nanoscale

Asymmetry in the biological world was considered by Pasteur as its universal property. Plants, animal and human tissues (pineal gland of brain, bones, skin, tendon, etc.) reveal pronounced ferroelectric and related properties such as second harmonic generation, linear electroptical, piezoelectric and pyroelectric effects. Helical, chiralic dissymmetry or low symmetry configuration of elementary biological building blocks (amino acids, peptide, proteins) allows to predict the existence of ferroelectricity and related phenomena in biological nanofibrillar structures. Another class of nanomaterials is man-made bioinspired materials, which are composed from chemically synthesized biomolecules and can self assemble into nanotubes (Fig. 1), nanospheres, hydrogels, etc. [1]. In this work we present our studies on intrinsic ferroelectric and related phenomena of dipeptide nanotubes (PNT) self-assembled by different techniques (Fig. 1), having different composition (aromatic and non-aromatic amino acids) and crystallographic symmetry [1, 2]. We found that peptide nanocrystalline subunits, composing these supramolecular nanostructures are characterized by strong piezoelectricity [3] (Fig. 2) and second harmonic generation effect based on their asymmetric structures. Some sorts of PNT such as diphenilalanine (FF)-PNT possess spontaneous electrical polarization which indicates on a new family of ferroelectricsbioinspired supramolecular ferroelectrics. We found that these nanoferroelectrics of biological origin demonstrate irreversible phase transitions around 150◦C which is characterized by dramatic changes of molecular structure, their crystalline symmetry and basic physical properties [4]. The symmetry variation (XRD data) from hexagonal asymmetric P61 space group to orthorhombic centrosymmetric Pmna results in disappearance of piezoelectric and second harmonic generation effects. The crystallographic symmetries for low and high phase are not linked by group-subgroup relations. We show that the observed phase transition occurs due to peptide molecular transformation from native linear FF molecules to FF-cyclopeptide (TOF-SIMS data) with reconstruction of covalent bonds. Lack of group-subgroup relation, breaking of covalent bonds between low and high temperature phases allows to relate this phase transition to reconstructive.

Peptide 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.