Browsing by Subject "self-assembly"

Now showing 1 - 7 of 7

Open Access
Characterization and corneal tissue engineering application of peptide amphiphiles
(2012) Dağdaş, Yavuz Selim
Molecular self-assembly is a powerful technique for developing novel nanostructures by using non-covalent interactions such as hydrogen bonding, hydrophobic, electrostatic, metal-ligand, π-π and van der Waals interactions. Hydrogen bonding, hydrophobic and electrostatic interactions promote self-assembly of peptide amphiphile molecules into nanofibers. Bundles of nanofibers form a three-dimensional network resulting in gel formation. Concentration and temperature dependent measurements of gel stiffness suggest that the mechanical properties of the gels are determined by a number of factors including the interfiber interactions and mechanical properties of individual nanofibers. Peptide amphiphile molecules provide a convenient model as extracellular matrix mimetic systems for regenerative medicine studies. Since the substrate stiffness is crucial for cellular behaviours such as proliferation, adhesion and differentiation, understanding the mechanisms behind the viscoelastic properties of the gels formed by self-assembling molecules can lead to development of new materials with controlled stiffness. In this study, regeneration of the corneal stroma was used as a model system for utilization of peptide amphiphile molecules in regenerative medicine studies. Corneal stroma is constituted by collagen fiber arrays that are closely packed forming a stiff environment for corneal fibroblasts. The tunability of mechanical properties of self-assembled peptide amphiphile nanostructures was aimed to be utilized in corneal stroma regeneration. Thinning of the corneal stroma is a debilitating problem that can be caused by diseases like keratoconus, infections or accidents. Since corneal stroma has a restricted regenerative capacity, thinning of stroma is usually treated with cornea transplantation, which is limited by the number of donors. In this thesis, I studied mechanical properties of self-assembled peptide amphiphile nanostructures in nanometer and micrometer scale. I found that the divergence in gel stiffness may arise from the difference of strength of interfiber bonds. An injectable, biocompatible, biodegradable and bioactive system that can be used for thickening the corneal stroma was developed. This system that is composed of nanofibers was observed to enhance viability and proliferation of keratocytes in vitro.
Open Access
Fabrication of an on-chip nanowire device with controllable nanogap for manipulation, capturing, and electrical characterization of nanoparticles
(2008) Uran, Can
One of the major challenges in nanofabrication commonly arises from the necessity to integrate nanostructures (e.g., nanoparticles) on the same chip with microcomponents (e.g., microelectrodes) that are orders-of-magnitude larger in size. For example, in order to make electrical contacts to colloidally synthesized nanoparticles (typically 1-100 nm in size) by integrating them with microelectrodes (typically in the few micrometers range on the critical side), a large size mismatch that easily ranges from 1:10 to 1:10,000 is required to be handled delicately for successful nano-to-micro integration. This necessitates the ability to manipulate and integrate nanoparticles with a sufficient level of precision on the microchip. In this thesis, to provide a convenient solution to this challenging problem, we proposed and demonstrated for the first time an onchip nanowire device that features a controllable nanogap in its architecture for capturing and electrical characterization of nanoparticles in the gap, all fully integrated on the same microchip. Our innovative approach relies on the use of dielectrophoretic electric-field assisted self-assembly of our segmented nanowires to construct a nanoscale device platform. For this purpose, we synthesized gold-silver-gold segmented nanowires and dielectrophoretically aligned them across our microfabricated array of electrodes. Subsequently, we selectively removed the middle silver segment to open a gap in the nanometer size between the self-aligned gold end segments. Using dielectrophoretic assembly once more, we captured nanoparticles in these nanogaps for further electrical characterization. One of the key benefits in our approach was that the aligned nanowires automatically provided electrical contacts to the captured nanoparticles to allow for electrical probing at the nanoscale. Our innovative approach enabled convenient full integration from nanoparticles to nanowires to microelectrodes to macroprobes on a single chip, spanning a size range of more than six orders of magnitude.
Open Access
Self-assembly of peptide nanofibers and their mechanical properties
(2012) Erkal, Turan Selman
Peptide nanofibers have been drawing attention because of their versatile, tailorable and functional properties in various research areas. The self-assembly mechanism of peptides and peptide amphiphile molecules is generally based on noncovalent interactions like hydrophobic, electrostatic and metal-ligand interactions. In this thesis, I investigated hydrophobic interaction of peptide amphiphiles (PAs) with other hydrophobic molecules and effect of pH change on self-assembly mechanism. The zinc phthalocyanine molecule was used as a hydrophobic probe to be encapsulated by peptide amphiphile molecules, which help to dissolve the molecule in water instead of an organic solvent. Charge neutralization of PAs by pH change led to nanofiber formation, which resulted in encapsulation and organization of zinc phthalocyanine molecules. The degree of self-assembly by pH change determined non-linear optical properties of zinc phthalocyanine molecule. Besides, morphological, mechanical and spectroscopic properties of phthalocyanine containing peptide nanofibers were characterized by TEM, SEM, oscillatory rheology, UV-Vis, fluorescence and circular dichroism spectroscopy. The mechanical properties of peptide and PA hydrogels and nanofibers have an essential place to determine applicability in different areas. Especially, PA and peptide molecules have been widely used in regenerative medicine studies and the stiffness of the extracellular matrix has a significant role on cellular behavior. In this thesis, viscoelastic properties of the peptide and PA gels were studied by oscillatory rheology. In addition to characterization of bulk mechanical properties of peptide gels, adhesion and stiffness of peptide nanofibers were determined by Atomic Force Microscopy.
Open Access
Supramolecular chiral self-assembled peptide nanostructures
(2016-01) Hatip, Meryem
Self-assembly process is an easy and convenient bottom-up technique for designing novel functional materials. Self-assembled peptide amphiphile (PA) molecules are remarkable building blocks for a wide-range of applications due to their easy synthesis, biocompatibility, biodegradabability and dynamic nature in aqueous conditions. Controlling self-assembly behavior still remains complex, since it can be affected by multiple factors. Chirality is an important parameter for designing and controlling self-assembled supramolecular nanomaterials. In this thesis, self-assembly mechanism of chiral peptide molecules was studied with different driving forces in order to develop new methodsfor producing self-assembled nanomaterials. In addition to self-assembly mechanism, different morphologies and chiral behaviors of the self-assembled supramolecular chiral peptide amphiphile nanostructureswere monitored with variouscharacterization methods. pH is a significant contributor for the self-assembly process and this effect was studied in detail to elucidate pH dependency of supramolecular conformation. According to morphological characterizations, histidine containing PA molecules form nanosheet like structures under acidic pH.At the isoelectric point of imidazole, they have a tendency to form twisted fiber or ribbon structures. Athigh pH iv conditions, pH 10, they form nanotubes due to the neutralization of imidazole groups and π-π interactionsat theside chain of histidine moiety.When another aromatic ring is included in the sequence, in this case phenylalanine residue, different nanostructures were observed. In addition to histidine PA, lysine and glutamic acid containing peptide building blocks were also studied to understand the effect of electrostatic interactions. Phenylalanine containing PAs and valine containing PAs were compared in terms of their chiral self-assembly behaviors. As a result of self-assembly of the positively charged and negatively charged peptides, well defined nanostructures were obtained. While valine containing PA molecules form straight nanofibers, phenyl alanine containing PAs form well ordered rigid twisted fibers and twisted ribbon structures.
Open Access
Synthesis and characterization of metallopeptide nanostructures
(2013) Ustahüseyin, Oya
Organic-inorganic hybrid structures play a number of distinguished roles in the living milieu. For instance, metal ions function as cofactors of enzymes and apatite mineralization in bone is driven by collagen nanofibers serve as both physical and chemical templates. These unique interactions in natural systems are examples for development of synthetic materials for many applications such as catalysts, artificial enzymes or materials for regenerative medicine etc. Manufacturing a catalyst at the nanoscale is important due to increased specific surface area and reduced diffusion path length. In this thesis, we demonstrated peptide based bioinspired nanomaterials. The self-assembled peptide nanofibers were utilized as templates for palladium nanoparticle formation. Functionalization of insoluble electrospun nanofibers with a heavy metal binding peptide sequence was utilized to remove toxic metal ions from water. In addition, peptide amphiphile nanofibers complexed with ZnII were used as enzyme mimics. The resulting nanostructures resemble natural bone alkaline phosphatase activity, which is a major enzyme for natural bone apatite formation.
Open Access
Targeted self-assembly of nanocrystal quantum dot emitters using smart peptide linkers on light emitting diodes
(2008) Zengin, Gülis
Semiconductor nanocrystal quantum dots find several applications in nanotechnology. Particularly in device applications, such quantum dots are typically required to be assembled with specific distribution in space for enhanced functionality and placed at desired spatial locations on the device which commonly has several diverse material components. In conventional approaches, self-assembly of nanocrystals typically takes place nonspecifically without surface recognition of materials and cannot meet these requirements. To remedy these issues, we proposed and demonstrated uniform, controlled, and targeted self-assembly of quantum dot emitters on multi-material devices by using cross-specificity of genetically engineered peptides as smart linkers and achieved directed immobilization of these quantum dot emitters decorated with peptides only on the targeted specific regions of our color-conversion LEDs. Our peptide decorated quantum dots exhibited 270 times stronger photoluminescence intensity compared to their negative control groups.
Open Access
Ultrahigh quality microlasers from controlled self-assembly of ultrathin colloidal semiconductor quantum wells
(Wiley-VCH GmbH, 2023-03-09) Thung, Yi Tian; Duan, Rui; Durmuşoğlu, Emek Göksu; He, Yichen; Xiao, Lian; Lee, Calvin Xiu Xian; Lew, Wen Siang; Zhang, Lin; Demir, Hilmi Volkan; Sun, Handong
Colloidal quantum wells (CQWs) have emerged as a promising class of gain material in various optical feedback configurations. This is due to their unique excitonic features arising from their 1D quantum confinement. However, existing methods for integrating CQW onto microresonators will cause low laser quality due to uneven CQW coating. To overcome this, the use of liquid-interface kinetically driven self-assembly is proposed to coat ultrathin, close-packed layers of colloidal CdSe/Cd1−xZnxS core/shell CQWs between 7 and 14 nm onto the surface of silica microsphere cavities. The fabricated CQW-whispering-gallery-mode microlasers possess a commendable high quality (Q) factor of 13 000 at room temperature. Stable single-mode lasing output is demonstrated through evanescent field coupling between a CQW-coated microsphere and a thin uncoated microfiber in a 2D-3D microcavity configuration. These promising results highlight the suitability of the liquid-interface kinetically driven self-assembly method for realizing ultrathin CQW-coated microlasers and its high compatibility for integrating colloidal nanocrystals onto complex 3D microstructures for future miniaturized colloidal optoelectronic and photonic applications.