Nanostructured Electrospun Fibers with Self-Assembled Cyclo-L-Tryptophan-L-Tyrosine Dipeptide as Piezoelectric Materials and Optical Second Harmonic Generators

The potential use of nanostructured dipeptide self-assemblies in materials science for energy harvesting devices is a highly sought-after area of research. Specifically, aromatic cyclo-dipeptides containing tryptophan have garnered attention due to their wide-bandgap semiconductor properties, high mechanical rigidity, photoluminescence, and nonlinear optical behavior. In this study, we present the development of a hybrid system comprising biopolymer electrospun fibers incorporated with the chiral cyclo-dipeptide L-Tryptophan-L-Tyrosine. The resulting nanofibers are wide-bandgap semiconductors (bandgap energy 4.0 eV) consisting of self-assembled nanotubes embedded within a polymer matrix, exhibiting intense blue photoluminescence. Moreover, the cyclo-dipeptide L-Tryptophan-L-Tyrosine incorporated into polycaprolactone nanofibers displays a strong effective second harmonic generation signal of 0.36 pm/V and shows notable piezoelectric properties with a high effective coefficient of 22 pCN-1, a piezoelectric voltage coefficient of geff=1.2 VmN-1 and a peak power density delivered by the nanofiber mat of 0.16μWcm-2. These hybrid systems hold great promise for applications in the field of nanoenergy harvesting and nanophotonics.

Solvent-dependent formation kinetics of L,L-diphenylalanine micro/nanotubes

Investigating the molecular mechanism underlying the aggregation process of amyloid fibers is of great importance both for its implications in several degenerative diseases and for the design of new materials based on self-assembly. In particular, micro/nanotubes of L,L-diphenylalanine have been investigated as a model of amyloid plaques in Alzheimer's disease and also for their broad range of physical properties, e.g., good thermo- and mechanical stability, semiconductivity, piezoelectricity and optical properties. It has been reported that the assembly/disassembly dynamics of L,L-diphenylalanine crystals is influenced by the solvent composition being triggered by evaporation of solvents. In fact the solvatomorphism of this peptide-based nanomaterial is complex and rich attracting great attention. Here we investigated the growing kinetics of the micro/nanotubes of L,L-diphenylalanine in samples prepared with toluene, ethanol, and acetic acid solvents by time-resolved Raman spectroscopy. Our results indicated that the self-assembly in this case competes with the water evaporation process contrary to what is reported by samples prepared with widely used solvent 1,1,1,3,3,3-hexafluoro-2-propanol. We note that exclusively tubular structures (being hollow for the toluene solvent case) were observed. Interestingly our results support the fact that for acetic acid, ethanol, and toluene the micro/nanotube formation process is autocatalytic instead of being nucleation-dominating as reported for samples prepared using solvent 1,1,1,3,3,3-hexafluoro-2-propanol.

Looking into a crystal ball: printing and patterning self-assembled peptide nanostructures

The solution processability of organic semiconductors and conjugated polymers along with the advent of nanomaterials as conducting inks have revolutionized next-generation flexible consumer electronics. Another equally important class of nanomaterials, self-assembled peptides, heralded as next-generation materials for bioelectronics, have a lot of potential in printed technology. In this minireview, we address the self-assembly process in dipeptides, their application in electronics, and recent progress in three-dimensional printing. The prospect of a generalizable path for nanopatterning self-assembled peptides using ice lithography and its challenges are further discussed.

Emerging trends of receptor-mediated tumor targeting peptides: A review with perspective from molecular imaging modalities

Natural peptides extracted from natural components such are known to have a relatively short in-vivo half-life and can readily metabolize by endo- and exo-peptidases. Fortunately, synthetic peptides can be easily manipulated to increase in-vivo stability, membrane permeability and target specificity with some well-known natural families. Many natural as well as synthetic peptides target to their endogenous receptors for diagnosis and therapeutic applications. In order to detect these peptides externally, they must be modified with radionuclides compatible with single photon emission computed tomography (SPECT) or positron emission tomography (PET). Although, these techniques mainly rely on physiological changes and have profound diagnostic strength over anatomical modalities such as MRI and CT. However, both SPECT and PET observed to possess lack of anatomical reference frame which is a key weakness of these techniques, and unfortunately, cannot be available freely in most clinical centres especially in under-developing countries. Hence, it is need of the time to design and develop economic, patient friendly and versatile strategies to grapple with existing problems without any hazardous side effects. Optical molecular imaging (OMI) has emerged as a novel technique in field of medical science using fluorescent probes as imaging modality and has ability to couple with organic drugs, small molecules, chemotherapeutics, DNA, RNA, anticancer peptide and protein without adding chelators as necessary for radionuclides. Furthermore, this review focuses on difference in imaging modalities and provides ample knowledge about reliable, economic and patient friendly optical imaging technique rather radionuclide-based imaging techniques.

Initial Aggregation and Ordering Mechanism of Diphenylalanine from Microsecond All-Atom Molecular Dynamics Simulations

Self-assembled diphenylalanine (FF) nanostructures have recently been demonstrated to be interesting materials for antibacterial and anticancer applications. These applications, among others, seek to take advantage of the high-order and resulting appealing physical properties of FF nanostructures by modifying the peptide in some way to achieve specific functionality. To rationally design modifications to the dipeptide that allow for this behavior, the driving forces of FF self-assembly must be understood. Molecular simulations have been utilized to assess these properties but have yielded conflicting conclusions due to inconsistencies in models chosen as well as the lack of quantitative analyses on the specific driving forces. Here, we present an all-atom explicit solvent molecular dynamics-based study on different length scales of FF aggregation. We utilize a free energy decomposition analysis as well as a dimer cluster analysis to identify the initial aggregation driving force to be FF intermolecular electrostatics, whereas solvent-mediated forces drive crystal growth. These data are consistent with the hypothesis that all hydrophobic dipeptides will have a similar initial aggregation mechanism until a critical aggregate size is reached, at which point crystallization occurs and subsequent crystal growth is dominated by solvent-mediated forces. We demonstrate that this proposed mechanism is testable by infrared spectroscopy focusing on the blueshift of the amide I peak as well as the ordering of the carboxylate peak.

Peptide Nanophotonics: From Optical Waveguiding to Precise Medicine and Multifunctional Biochips

Optical waveguiding phenomena found in bioinspired chemically synthesized peptide nanostructures are a new paradigm which can revolutionize emerging fields of precise medicine and health monitoring. A unique combination of their intrinsic biocompatibility with remarkable multifunctional optical properties and developed nanotechnology of large peptide wafers makes them highly promising for new biomedical light therapy tools and implantable optical biochips. This Review highlights a new field of peptide nanophotonics. It covers peptide nanotechnology and the fabrication process of peptide integrated optical circuits, basic studies of linear and nonlinear optical phenomena in biological and bioinspired nanostructures, and their passive and active optical waveguiding. It is shown that the optical properties of this generation of bio-optical materials are governed by fundamental biological processes. Refolding the peptide secondary structure is followed by wideband optical absorption and visible tunable fluorescence. In peptide optical waveguides, such a bio-optical effect leads to switching from passive waveguiding mode in native α-helical phase to an active one in the β-sheet phase. The found active waveguiding effect in β-sheet fiber structures below optical diffraction limit opens an avenue for the future development of new bionanophotonics in ultrathin peptide/protein fibrillar structures toward advanced biomedical nanotechnology.

SERS active self-assembled diphenylalanine micro/nanostructures: A combined experimental and theoretical investigation

Enhancing Raman signatures of molecules by self-assembled metal nanoparticles, nanolithography patterning, or by designing plasmonic nanostructures is widely used for detection of low abundance biological systems. Self-assembled peptide nanostructures provide a natural template for tethering Au and Ag nanoparticles due to its fractal surface. Here, we show the use of L,L-diphenylalanine micro-nanostructures (FF-MNSs) for the organization of Ag and Au nanoparticles (Nps) and its potential as surface-enhanced Raman scattering (SERS)-active substrates. The FF-MNSs undergo an irreversible phase transition from hexagonally packed (hex) micro-nanotubes to an orthorhombic (ort) structure at ∼150 °C. The metal Nps form chains on hex FF-MNSs as inferred from transmission electron microscopy images and a uniform non-aggregated distribution in the ort phase. The high luminescence from the ort FF-MNS phase precludes SERS measurements with AgNps. The calculated Raman spectra using density-functional theory shows a higher intensity from rhodamine 6G (R6G) molecule in the presence of an Ag atom bound to ort FF compared with hex FF. The SERS spectra obtained from R6G bound to FF-MNSs with AuNps clearly show a higher enhancement for the ort phase compared with hex FF, corroborating our theoretical calculations. Our results indicate that FF-MNSs both in the hex and ort phases can be used as substrates for the SERS analysis with different metal nanoparticles, opening up a novel class of optically active bio-based substrates.

Multicomponent peptide assemblies

Self-assembled peptide nanostructures have been increasingly exploited as functional materials for applications in biomedicine and energy. The emergent properties of these nanomaterials determine the applications for which they can be exploited. It has recently been appreciated that nanomaterials composed of multicomponent coassembled peptides often display unique emergent properties that have the potential to dramatically expand the functional utility of peptide-based materials. This review presents recent efforts in the development of multicomponent peptide assemblies. The discussion includes multicomponent assemblies derived from short low molecular weight peptides, peptide amphiphiles, coiled coil peptides, collagen, and β-sheet peptides. The design, structure, emergent properties, and applications for these multicomponent assemblies are presented in order to illustrate the potential of these formulations as sophisticated next-generation bio-inspired materials.