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Amyloid Directed Synthesis of Titanium Dioxide Nanowires and Their Applications in Hybrid Photovoltaic Devices
Advanced Functional Materials
Abstract
This paper reports beta-lactoglobulin amyloid protein fibrils directed synthesis of Titanium Dioxide (TiO2) hybrid nanowires. Protein fibrils act as templates to generate closely packed TiO2 nanoparticles on the surface of the fibrils using titanium (IV) bis (ammonium lactato) dihydroxide (TiBALDH) as precursor, resulting in the TiO2coated amyloid hybrid nanowires. These amyloid fibrils also exhibit complexation with a luminescent water-soluble semiconductive polythiophene (P3HT). TiO2 nanowires behave as electron acceptor while, P3HT as electron donor. In this way, amyloid-TiO2 hybrid nanowires can serve in heterojunction photovoltaic devices. To demonstrate this, a photovoltaic active layer is prepared by spin coating the blended mixture of polythiophene-coated fibrils and amyloid-TiO2 hybrid nanowires. The currentvoltage characteristics of these photovoltaic devices exhibit excellent fill factor of 0.53, photovoltaic current density of 3.97 mAcm-2 and power conversion efficiency of 0.72%, highlighting a possible future role for amyloid-based templates in donoracceptor devices, organic electronics and hybrid solar cells.
... Self-assembled amyloid-like peptides have emerged as a unique class of materials with potential applications as soft templates for nanotube and nanowire growth [141,142]. Mezzenga et al. used amyloid-like peptides as soft templates to direct the mineralization process of titania [143]. Particularly, β-lactoglobulin amyloid protein with self-assembled fibrillar nanostructures was also employed as template for the synthesis of titania-based hybrid nanowires. ...
... Particularly, β-lactoglobulin amyloid protein with self-assembled fibrillar nanostructures was also employed as template for the synthesis of titania-based hybrid nanowires. The titania nanoparticles were sintered uniformly, thus producing a rather homogeneous layer with the thickness of 20-25 nm on the surface of the protein fibrils, which can serve in heterojunction photovoltaic devices (Fig. 17) [143]. Mezzenga et al. also prepared a photovoltaic active layer by spin coating the blended mixture of polythiophenecoated fibrils and amyloid-titania hybrid nanowires. ...
... TiO 2 nanowires behave as electron acceptor while, polythiophene as electron donor. These photovoltaic devices exhibited enhanced fill factor, increased photovoltaic current density and much higher power conversion efficiency in comparison with photovoltaic solar cells based on fully organic homologue active layers [143]. The individual encapsulation of living cells has a great impact on the areas of single cell-based sensors and devices as well as funda-mental studies in single cell-based biology, which promises the potential of chemically manipulating cellular activities (e.g., cell division) at the single-cell level and protecting cells from external stressors. ...
... These nanowires are then complexed with water-soluble semiconductor thiophene to act as electron donors and acceptors, respectively. They can be used in heterojunction photovoltaic devices and, in the future, in organic electronics and hybrid solar cells [43,44]. Grafting functional units onto the target in the form of grafting is also one of the commonly used methods for functionalization. ...
... (a) Modification of amyloid fibrils, reproduced from ref.[43], Wiley. (b) Processing of amyloid fibrils into two-dimensional membrane materials, reproduced from ref.[49], Nature Publishing Group. ...
Amyloid fibrils are one of the important forms of protein aggregates, first discovered in the pathological brain tissues of patients with various neurodegenerative diseases. They are considered the core pathological markers of different neurodegenerative diseases. In recent years, research has found that multiple proteins or peptides dynamically assemble to form functional amyloid-like nanofibrils under physiological conditions, exhibiting excellent mechanical properties, high environmental stability, and self-healing ability. Therefore, they have become a class of functional biological nanomaterials with important development potential. This article systematically reviews the latest progress in the preparation, functionalization, and application of amyloid-like nanofibrils in engineering and provides an outlook on possible future development directions.
... The multiple benefits of using amyloid fibrils to template the active layer in optoelectronic devices, converting either electricity into light (LEDs) or solar energy into electricity (photovoltaic solar cells, PSCs), have been demonstrated by Inganas' group on fully organic devices 645−648 and by our group on hybrid devices. 649 The role of amyloids has been shown to be many-fold: increase in external quantum efficiency (EQE) by more than 1 order of magnitude, outstanding power conversion efficiency (PCE), high charge mobility, as reflected by the fill factor (FF), and high charge generation, as indicated by high short-circuit currents J SC . ...
... An alternative approach to use amyloids to assist the formation of the active layer in hybrid photovoltaic cells was proposed by Bolisetty et al. 649 In this approach, the amyloid fibrils were made of β-lactoglobulin and played a crucial role in the design of the active layer: they were first blended with TiBALDH precursor to template TiO 2 nanoparticles directly on the surface of the amyloids, as a first electron acceptor pseudocomponent, then β-lactoglobulin was mixed with polytiophene to form the electron donor pseudocomponent, the two were then assembled into an active layer of a sandwiched photovoltaic hybrid cell. Importantly, the resulting device was found to have a fill factor (FF) as high as 0.53 and a power conversion efficiency approaching 1% (0.72%). ...
For each kilogram of food protein wasted, between 15 and 750 kg of CO2 end up in the atmosphere. With this alarming carbon footprint, food protein waste not only contributes to climate change but also significantly impacts other environmental boundaries, such as nitrogen and phosphorus cycles, global freshwater use, change in land composition, chemical pollution, and biodiversity loss. This contrasts sharply with both the high nutritional value of proteins, as well as their unique chemical and physical versatility, which enable their use in new materials and innovative technologies. In this review, we discuss how food protein waste can be efficiently valorized not only by reintroduction into the food chain supply but also as a template for the development of sustainable technologies by allowing it to exit the food-value chain, thus alleviating some of the most urgent global challenges. We showcase three technologies of immediate significance and environmental impact: biodegradable plastics, water purification, and renewable energy. We discuss, by carefully reviewing the current state of the art, how proteins extracted from food waste can be valorized into key players to facilitate these technologies. We furthermore support analysis of the extant literature by original life cycle assessment (LCA) examples run ad hoc on both plant and animal waste proteins in the context of the technologies considered, and against realistic benchmarks, to quantitatively demonstrate their efficacy and potential. We finally conclude the review with an outlook on how such a comprehensive management of food protein waste is anticipated to transform its carbon footprint from positive to negative and, more generally, have a favorable impact on several other important planetary boundaries.
... Amyloids can be used for optoelectronic applications by modifying the amyloid surface with functional materials, such as proteins and polymers [9]. For example, hybrid nanowires created by coating amyloids made from β-lactoglobulin with titanium dioxide (TiO 2 ) and polythiophene could work as photovoltaic devices with excellent power conversion efficiency, making them promising candidates for use in hybrid solar cells [17]. Functionalization of the amyloid surface was achieved using a biotinstreptavidin system; the amyloids were modified with biotin through co-incubation with a protein peptide and biotin, and labeled streptavidin was attached to the amyloids via biotin-streptavidin interactions [18,19]. ...
Protein amyloids have attracted attention for their application as functional amyloid materials because of their strong properties, such as high resistance to chemical or biological degradation, despite their medical issues. Amyloids can be used for various applications by modifying the amyloid surface with functional materials, such as proteins and polymers. In this study, we investigated the effect of polyallylamine (PAA), a functional cationic polymer as a candidate for amyloid modification, on the amyloids formed from amyloid β (Aβ) peptide. It was demonstrated for the first time that PAA can bind to Aβ amyloids through fluorescence observations and the quenched emission from the tyrosine at site 10 near the fibrillogenic core. These results suggest that PAA could be used to develop new functional amyloids. However, notably, coating Aβ amyloid with PAA could affect conventional amyloid detection assays such as thioflavin T assay and detection using antibodies. Thus, our results also indicate that consideration would be necessary for the analysis of functional amyloids coated with various polymers.
... Currently, amyloid fibrils also capture interest in the field of nanotechnology, as they can act as a scaffolding to a wide range of (in)organic building blocks resulting in materials of extraordinary mechanical and optical properties. [9,10] Amyloid-based nanomaterials can find applications in various areas ( Figure 1) including biomedicine (among others in antitumor therapy, [11,12] as drug-delivering agents, [13] cell scaffolds [14] or artificial tissues [15,16] and technology (in photovoltaics, [17] catalysis, [18] optoelectronics, [19][20][21] as nanocomposites/hybrid materials [22,23] and biosensors [24] ). To achieve intended functionalities, a plethora of macroscopic structures: bulk gels, films, fibers, as well as micro-or nanogels and condensates of protein fibrils are achievable. ...
Amyloid fibrils are supramolecular systems showing distinct chirality at different levels of their complex multilayered architectures. Due to the regular long‐range chiral organization, amyloid fibrils exhibit the most intense Vibrational Optical Activity (VOA) signal observed up to now, making VOA techniques: Vibrational Circular Dichroism (VCD) and Raman Optical Activity (ROA) very promising tools to explore their structures, handedness and intricate polymorphism. This concept article reviews up‐to‐date experimental studies on VOA applications to investigate amyloid fibrils highlighting its future potential in analyzing of these unique supramolecular systems, in particular in the context of biomedicine and nanotechnology.
... [11][12][13][14] Amyloid-like protein brils have been used successfully for templating metallic nanowires. 11,[15][16][17] Fabricating nanoscale amyloid-inorganic hybrid materials using amyloid protein bers is interesting because these scaffolds present high aspect ratios and generally display multiple binding sites for small molecules, cations or nanoparticles along their surface for the design of nanocomposites through specic postfunctionalization or in situ approaches. [18][19][20] In addition to their regularity and ready production, these biological templates may have another key advantage, as they can grow directly on the required surfaces, thus guiding the assembly of the inorganic nanostructures straight onto the nanodevices and eliminating the positioning and micro-manipulation stage. ...
Gold-metallic nanofibrils were prepared from three different iso-apoferritin (APO) proteins with different Light/Heavy (L/H) subunit ratios (from 0% up to 100% L-subunits). We show that APO protein fibrils have the ability to in situ nucleate and grow gold nanoparticles (AuNPs) simultaneously assembled on opposite strands of the fibrils, forming hybrid inorganic-organic metallic nanowires. The AuNPs are arranged following the pitch of the helical APO protein fiber. The mean size of the AuNPs was similar in the three different APO protein fibrils studied in this work. The AuNPs retained their optical properties in these hybrid systems. Conductivity measurements showed ohmic behavior like that of a continuous metallic structure.
... For example, biotic nanomaterials, based on highly chiral and ordered nanofibril scaffolds, show versatile prospective optoelectronic and photonic applications. [105][106][107] The central general question to answer using VCD is what is the impact of the handedness and chiral polymorphism on architectures, stability and reversibility of amyloid fibrils. ...
Vibrational optical activity (VOA) refers to two vibrational techniques: vibrational circular dichroism (VCD) and Raman optical activity (ROA) that are sensitive both to the chirality and the molecular structure, typically surpassing electronic optical activity (EOA) in recognition of fine structural details. However, the measurement of VOA is inherently obstructed as the intensity of the VOA signal is typically 10-4-10-5 of the intensity of the parent IR or Raman signals. This feature considerably limits the practical applications of VOA and is a fundamental reason why various strategies are currently developed to enhance the VOA intensity. This perspective review discusses up-to-date studies focusing on applications of VOA to analyse supramolecular, mostly biogenic, systems showing induction and amplification of chirality. Most attention is devoted to two types of biogenic supramolecular assemblies providing unique enhancement of VOA: amyloid fibrils showing enormous VCD and carotenoid aggregates exhibiting resonantly enhanced ROA.
... An in-depth examination of the binding between nano-Pd and AFs by Fourier transform infrared spectroscopy (FTIR) revealed peaks at 1250 cm À 1 , 1530 cm À 1 , and 1663 cm À 1 for amide I, amide II, and amide III, respectively, suggesting the characteristic signatures of AFs (Figure 2b). [13] These results confirmed the high-density cross-linkage of nano-Pd and the CP surface bridged by AFs. ...
Electrocatalysis offers great promise for water purification but is limited by low active area and high uncontrollability of electrocatalysts. To overcome these constraints, we propose hybrid bulk electrodes by synthesizing and binding a Pd nanocatalyst (nano‐Pd) to the electrodes via amyloid fibrils (AFs). The AFs template is effective for controlling the nucleation, growth, and assembly of nano‐Pd on the electrode. In addition, the three‐dimensional hierarchically porous nanostructure of AFs is beneficial for loading high‐density nano‐Pd with a large active area. The novel hybrid cathodes exhibit superior electroreduction performance for the detoxification of hexavalent chromium (Cr⁶⁺), 4‐chlorophenol, and trichloroacetic acid in wastewater and drinking water. This study provides a proof‐of‐concept design of an AFs‐templated nano‐Pd‐based hybrid electrode, which constitutes a paradigm shift in electrocatalytic water purification, and broadens the horizon of its potential engineered applications.
... In the case of water soluble conjugated polymers a co-solvent is not required. 233 In a pioneering study, LEDs were prepared where the active layer consisted of an electroluminescent blue emitting polymer and PNFs. Compared to a control device without PNFs the device with PNFs was about 10 times more efficient. ...
he development towards a sustainable society requires a radical change of many of the materials we currently use. Besides the replacement of plastics, derived from petrochemical sources, with renewable alternatives, we will also need functional materials for applications in areas ranging from green energy and environmental remediation to smart foods. Proteins could, with their intriguing ability of self-assembly into various forms, play important roles in all these fields. To achieve that, the code for how to assemble hierarchically ordered structures similar to the protein materials found in nature must be cracked. During the last decade it has been demonstrated that amyloid-like protein nanofibrils (PNFs) could be a steppingstone for this task. PNFs are formed by self-assembly in water from a range of proteins, including plant resources and industrial side streams. The nanofibrils display distinct functional features and can be further assembled into larger structures. PNFs thus provide a framework for creating ordered, functional structures from the atomic level up to the macroscale. This review address how industrial scale protein resources could be transformed into PNFs and further assembled into materials with specific mechanical and functional properties. We describe what is required from a protein to form PNFs and how the structural properties at different length scales determine the material properties. We also discuss potential chemical routes to modify the properties of the fibrils and to assemble them into macroscopic structures.
... 3 Amyloid-like aggregates can occur in different forms and various sizes: from elongated fibrils and dense microparticles (particulates) to core−shell structures (spherulites) and nanotubes. 11−15 Fibrils are particularly suited for the development of three-dimensional cell culture scaffolds, tissue engineering, and inorganic patterning 7,16,17 as well as for organic templates for metals and semiconductors 18 and coating materials for functionalized biosensors. 15,19 Core−shell structures have shown their potential as a drug delivery system for sustained release, 20 and engineering protein microparticles are used to enhance pulmonary delivery of proteins and peptides. ...
De novo designed protein supramolecular structures are nowadays attracting much interest as highly performing biomaterials. While a clear advantage is provided by the intrinsic biocompatibility and biodegradability of protein and peptide building blocks, developing sustainable and green bottom up approaches for finely tuning the material properties still remains a challenge. Here, we present an experimental study on the formation of protein microparticles in the form of particulates from the protein α-lactalbumin using bulk mixing in water solution and high temperature. Once formed, the structure and stability of these spherical protein condensates change upon further thermal incubation while the size of aggregates does not significantly increase. Combining advanced microscopy and spectroscopy methods, we prove that this process, named maturation, is characterized by a gradual increase of amyloid-like structure in protein particulates, an enhancement in surface roughness and in molecular compactness, providing a higher stability and resistance of the structure in acidic environments. When dissolved at pH 2, early stage particulates disassemble into a homogeneous population of small oligomers, while the late stage particulates remain unaffected. Particulates at the intermediate stage of maturation partially disassemble into a heterogeneous population of fragments. Importantly, differently matured microparticles show different features when loading a model lipophilic molecule. Our findings suggest conformational transitions localized at the interface as a key step in the maturation of amyloid protein condensates, promoting this phenomenon as an intrinsic knob to tailor the properties of protein microparticles formed via bulk mixing in aqueous solution. This provides a simple and sustainable platform for the design and realization of protein microparticles for tailored applications.
... In a study of Bolisetty et al. 310 , they first developed amyloid fibrils, an inorganic oxide (TiO2), and π-conjugated polymers (polythiophene (P3HT)) based hybrid material capable of serving in heterojunction photovoltaic solar cell. To synthesize TiO2-coated amyloid hybrid nanowires, protein fibrils act as templates to produce closely packed TiO2 nanoparticles on the surface of the fibrils, while titanium (IV) bis (ammonium lactate) dihydroxide was used as a precursor. ...
... Review retention at 20 A/g, retaining 99.2% of initial specific capacitance after even 5000 cycles. 308 Bolisetty et al. 309 developed a hybrid material based on amyloid fibrils, an inorganic oxide (TiO 2 ), and π-conjugated polymers (polythiophene (P3HT)) capable of serving in a heterojunction photovoltaic solar cell. In synthesis of TiO 2coated amyloid hybrid nanowires, protein fibrils act as templates to produce closely packed TiO 2 nanoparticles on the surface of the fibrils, while titanium(IV) bis (ammonium lactate) dihydroxide was used as a precursor. ...
Researchers have recently focused on the advancement of new materials from biorenewable and sustainable sources because of great concerns about the environment, waste accumulation and destruction, and the inevitable depletion of fossil resources. Biorenewable materials have been extensively used as a matrix or reinforcement in many applications. In the development of innovative methods and materials, composites offer important advantages because of their excellent properties such as ease of fabrication, higher mechanical properties, high thermal stability, and many more. Especially, nanocomposites (obtained by using biorenewable sources) have significant advantages when compared to conventional composites. Nanocomposites have been utilized in many applications including food, biomedical, electroanalysis, energy storage, wastewater treatment, automotive, etc. This comprehensive review provides chemistry, structures, advanced applications, and recent developments about nanocomposites obtained from biorenewable sources.
... Self-assembling molecules are increasingly used for the production of polymeric materials, fibrous assemblies and hydrogels with applications as diverse as photovoltaic cells [22] to platforms for tissue engineering [23]. Amyloid fibrils are extremely strong and stable structures [24,25], resistant to degradation and can be strengthened even further with intermolecular crosslinking [26,27]. ...
... 15 These particulate proteins have a narrow size distribution, relatively high sphericity and various functional groups, which enable them to be used in a wide range of fields from food processing, [16][17][18] and drug delivery [19][20][21] to more recently soft-electronics. [22][23][24][25] However, there is no report of stabilizing protein particles by a thin coating of p-conjugated polymer and carbon for advanced applications in nanoelectronics. ...
We demonstrate a versatile and facile method for fabrication of a new class of amphiphilic spherical nanoparticles having nitrogen-enriched carbonised surface and precisely-controlled morphology, which are prepared by one-pot polymerization...
... Owing to high thermal stability, stiffness, biocompatibility, and controllable selfassembly (6,7); amyloids are emerging as novel class of biological nanomaterials. They have found applications in the areas of food science, materials science, medicine and electronics (8)(9)(10)(11)(12). Amyloid fibrils have also been hybridized with graphene and DNA origami to develop hybrid biomaterials (7,(13)(14)(15). ...
Amyloid fibrils are associated with many neurodegenerative diseases, motivating investigations into their structure and function. Although not linked to a specific disease, albumins have been reported to form many structural aggregates. We were interested in investigating host immune responses to amyloid fibrils assembled from the model protein ovalbumin. Surprisingly, upon subjecting ovalbumin to standard denaturing conditions, we encountered giant protein nanosheets harbouring amyloid-like features and hypothesized that these nanosheets might have potential in clinical or therapeutic applications. We found that the nanosheets, without the administration of any additional adjuvant, evoked a strong antibody response in mice that was higher than that observed for native ovalbumin. This suggests that amyloid nanosheets have self-adjuvanting property. The nanosheet-induced immune response was helper T cell 2 (Th2) biased and negligibly inflammatory. While testing whether the nanosheets might form depots for the sustained release of precursor proteins, we did observe release of ovalbumin that mimicked the conformation of native protein. Moreover, the nanosheets could load the anticancer drug doxorubicin and release it in a slow and sustained manner. Taken together, our results suggest that amyloid nanosheets should be further investigated as either an antigen delivery vehicle or as a multifunctional antigen and drug co-delivery system, with potential applications in simultaneous immunotherapy and chemotherapy.
... Key examples of such pathologies include Alzheimerʼs disease, Parkinsonʼs disease, sickle-cell anemia and type-II diabetes, which are associated with the formation in the human brain or other organs of filamentous protein assemblies commonly known as amyloid fibrils [13][14][15][16][17][18][19][20][21][22][23][24]. Finally, due to their unique physicochemical properties, self-assembled filamentous structures can be used as biomaterials for many applications in nanotechnology [25][26][27][28][29][30][31]. ...
The growth of filamentous aggregates from precursor proteins is a process of central importance to both normal and aberrant biology, for instance as the driver of devastating human disorders such as Alzheimer's and Parkinson's diseases. The conventional theoretical framework for describing this class of phenomena in bulk is based upon the mean-field limit of the law of mass action, which implicitly assumes deterministic dynamics. However, protein filament formation processes under spatial confinement, such as in microdroplets or in the cellular environment, show intrinsic variability due to the molecular noise associated with small-volume effects. To account for this effect, in this paper we introduce a stochastic differential equation approach for investigating protein filament formation processes under spatial confinement. Using this framework, we study the statistical properties of stochastic aggregation curves, as well as the distribution of reaction lag-times. Moreover, we establish the gradual breakdown of the correlation between lag-time and normalized growth rate under spatial confinement. Our results establish the key role of spatial confinement in determining the onset of stochasticity in protein filament formation and offer a formalism for studying protein aggregation kinetics in small volumes in terms of the kinetic parameters describing the aggregation dynamics in bulk.
... Self-assembling molecules are increasingly used for the production of polymeric materials, fibrous assemblies and hydrogels with applications as diverse as photovoltaic cells [22] to platforms for tissue engineering [23]. Amyloid fibrils are extremely strong and stable structures [24,25], resistant to degradation and can be strengthened even further with intermolecular crosslinking [26,27]. ...
Amyloidogenic peptides are well known for their involvement in diseases such as type 2 diabetes and Alzheimer’s disease. However, more recently, amyloid fibrils have been shown to provide scaffolding and protection as functional materials in a range of organisms from bacteria to humans. These roles highlight the incredible tensile strength of the cross-b amyloid architecture. Many amino acid sequences are able to self-assemble to form amyloid with a cross-b core. Here we describe our recent advances in understanding how sequence contributes to amyloidogenicity and structure. For example, we describe penta- and hexapeptides that assemble to form different morphologies; a 12mer peptide that forms fibrous crystals; and an eightresidue peptide originating from a-synuclein that has the ability to form nanotubes. This work provides a wide range of peptides that may be exploited as fibrous bionanomaterials. These fibrils provide a scaffold upon which functional groups may be added, or templated assembly may be performed. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
... Bolisetty et al. utilized b-lactoglobulin amyloid fibrils as templates to successfully direct the synthesis of closely packed TiO 2 hybrid nanowires. 432 Due to the well-organized combination of electrostatic and hydrogen bond interactions, TiO 2 nanoparticles decorated the surfaces of the protein fibrils uniformly. Subsequently, the TiO 2 -coated amyloid hybrid nanowires could be prepared into a photovoltaic active layer by spincoating a blended mixture of polythiophene-coated fibrils and amyloid-TiO 2 hybrid nanowires (Fig. 30b). ...
Self-assembled peptide and protein amyloid nanostructures have traditionally been considered only as pathological aggregates implicated in human neurodegenerative diseases. In more recent times these nanostructures have found interesting applications as advanced materials in biomedicine, tissue engineering, renewable energy, environmental science, nanotechnology and material science, to name only a few fields. In all these applications, the final function depends on: i) the specific mechanisms of protein aggregation, ii) the hierarchical structure of the protein and peptide amyloids from atomistic to mesoscopic length scales, and iii) the physical properties of the amyloids in the context of their surrounding environment (biological or artificial). In this review we will discuss recent progress made in the field of functional and artificial amyloids and highlight connections between protein/peptide folding, unfolding, and aggregation mechanisms, with resulting amyloid structure and functionality. We also highlight current advances in the design and synthesis of amyloid-based biological and functional materials and identify new potential fields in which amyloid-based structures promise new breakthroughs.
... The self-assembly properties [1,4,5] and high stability [6,7] of amyloid fibrils suggest the potential to utilize them as bionanomaterials [8]. Previous research has demonstrated the functionalization of fibrils for various applications such as biosensors [9][10][11][12][13], nanowires [14][15][16], nanocomposites [17,18], thin films [19], nanoporous matrices [20], hydrogels [21], and aerogels [22]. Their stability over a broad-range of temperatures, pHs, solvents, and proteases, allows amyloid fibrils to be exploited for many applications [13,23]. ...
Amyloid fibrils are a class of insoluble protein nanofibers that are formed via the self-assembly of a wide range of peptides and proteins. They are increasingly exploited for a broad range of applications in bionanotechnology, such as biosensing and drug delivery, as nanowires, hydrogels, and thin films. Amyloid fibrils have been prepared from many proteins, but there has been no definitive characterization of amyloid fibrils from hemoglobin to date. Here, nanofiber formation was carried out under denaturing conditions using solutions of apo-hemoglobin extracted from bovine waste blood. A characteristic amyloid fibril morphology was confirmed by transmission electron microscopy (TEM) and atomic force microscopy (AFM), with mean fibril dimensions of approximately 5 nm diameter and up to several microns in length. The thioflavin T assay confirmed the presence of β-sheet structures in apo-hemoglobin fibrils, and X-ray fiber diffraction showed the characteristic amyloid cross-β quaternary structure. Apo-hemoglobin nanofibers demonstrated high stability over a range of temperatures (−20 to 80 °C) and pHs (2–10), and were stable in the presence of organic solvents and trypsin, confirming their potential as nanomaterials with versatile applications. This study conclusively demonstrates the formation of amyloid fibrils from hemoglobin for the first time, and also introduces a cost-effective method for amyloid fibril manufacture using meat industry by-products.
... Several examples of functional amyloid materials, with analogous molecular-level characteristics as their pathogenic counterparts, have in fact been found inside biological organisms ranging from bacteria to humans [18]. This discovery has provided a source of inspiration for the application of synthetic, amyloid-like structures in bio-, nano-, and microtechnology [19][20][21][22][23][24][25][26][27][28]. ...
The polymerization of proteins and peptides into filamentous supramolecular structures is an elementary form of self-organization of key importance to the functioning biological systems, as in the case of actin biofilaments that compose the cellular cytoskeleton. Aberrant filamentous protein self-assembly, however, is associated with undesired effects and severe clinical disorders, such as Alzheimer's and Parkinson's diseases, which, at the molecular level, are associated with the formation of certain forms of filamentous protein aggregates known as amyloids. Moreover, due to their unique physicochemical properties, protein filaments are finding extensive applications as biomaterials for nanotechnology. With all these different factors at play, the field of filamentous protein self-assembly has experienced tremendous activity in recent years. A key question in this area has been to elucidate the microscopic mechanisms through which filamentous aggregates emerge from dispersed proteins with the goal of uncovering the underlying physical principles. With the latest developments in the mathematical modeling of protein aggregation kinetics as well as the improvement of the available experimental techniques it is now possible to tackle many of these complex systems and carry out detailed analyses of the underlying microscopic steps involved in protein filament formation. In this paper, we review some classical and modern kinetic theories of protein filament formation, highlighting their use as a general strategy for quantifying the molecular-level mechanisms and transition states involved in these processes.
... Metallic conductivity can be provided by fibre metallization 12 and semiconducting behaviours can result from the intrinsic properties of self-assembled fibres given by π-stacked aromatics or charged groups at their surfaces [13][14][15][16][17][18][19] . They can also be incorporated into hybrid devices with luminescent or shape-memory properties [20][21][22][23] . Furthermore, it has been shown that it is possible to unfold and refold a protein bound on the surface of an amyloid fibre 24 . ...
Engineering bioelectronic components and set-ups that mimic natural systems is extremely challenging. Here we report the design of a protein-only redox film inspired by the architecture of bacterial electroactive biofilms. The nanowire scaffold is formed using a chimeric protein that results from the attachment of a prion domain to a rubredoxin (Rd) that acts as an electron carrier. The prion domain self-assembles into stable fibres and provides a suitable arrangement of redox metal centres in Rd to permit electron transport. This results in highly organized films, able to transport electrons over several micrometres through a network of bionanowires. We demonstrate that our bionanowires can be used as electron-transfer mediators to build a bioelectrode for the electrocatalytic oxygen reduction by laccase. This approach opens opportunities for the engineering of protein-only electron mediators (with tunable redox potentials and optimized interactions with enzymes) and applications in the field of protein-only bioelectrodes. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
... 35 Moreover, β-LG fibril is also a good template for the synthesis of inorganic nanomaterials. For instance, Mezzenga and co-workers synthesized metal (gold, silver, and palladium) nanoparticles, 36 gold single crystals, 37−39 TiO 2 nanowires, 40 and Fe 3 O 4 /β-LG fibrils (or nanoclusters) hybrids 41 for diverse applications. Because of its high strength and easy availability, 42 the β-LG fibril is a promising candidate to serve as the catalyst scaffold for the construction of the metal NP-loaded CMRs. ...
A catalytic membrane reactor, which contains a membrane matrix and a catalytic film of alloy nanoparticle-loaded β-lactoglobulin fibrils (NPs@β-LGF), was developed for the continuous-flow reduction of 4-nitrophenol (4-NP). The Cu-Ag and Cu-Ag-Au alloy NPs were synthesized using β-LGF as a scaffold and stabilizing agent. In this process, the Cu nanoclusters were formed in the initial stage and were able to promote the synthesis of Ag0, which acts as a reducing agent for the rapid formation of Au0. Furthermore, a catalytic membrane reactor was constructed by depositing the NPs@β-LGFs on a membrane matrix. The catalytic activity of the Cu-Ag-Au alloy NPs was higher than that of the Cu-Ag alloy NPs, using the reduction of 4-NP to 4-AP as a model reaction. The observed rate constant in the continuous-flow system is also higher than that in the batch system. In addition, these catalytic membrane reactors had good operating stability and antibacterial activity.
... The unique mechanical behaviour of the amyloid like peptide assemblies contributedto the design of functional materials including conductive fibres, energy harvesting systems or tissue scaffolds [368][369][370][371][372]. Cross-β sheet organization, excess hydrogen bonding and aromatic interactions between the amyloid-based peptides are the inherent sources of the mechanical stability and rigidity of the amyloid derived peptide assemblies [373]. ...
Nature is an important inspirational source for scientists, and presents complex and elegant examples of adaptive and intelligent systems created by self-assembly. Significant effort has been devoted to understanding these sophisticated systems. The self-assembly process enables us to create supramolecular nanostructures with high order and complexity, and peptide-based self-assembling building blocks can serve as suitable platforms to construct nanostructures showing diverse features and applications. In this review, peptide-based supramolecular assemblies will be discussed in terms of their synthesis, design, characterization and application. Peptide nanostructures are categorized based on their chemical and physical properties and will be examined by rationalizing the influence of peptide design on the resulting morphology and the methods employed to characterize these high order complex systems. Moreover, the application of self-assembled peptide nanomaterials as functional materials in information technologies and environmental sciences will be reviewed by providing examples from recently published high-impact studies.
We here explore confinement-induced assembly of whey protein nanofibrils (PNFs) into microscale fibers using microfocused synchrotron X-ray scattering. Solvent evaporation aligns the PNFs into anisotropic fibers, and the process is followed in situ by scattering experiments within a droplet of PNF dispersion. We find an optimal temperature at which the order parameter of the protein fiber is maximized, suggesting that the degree of order results from a balance between the time scales of the forced alignment and the rotational diffusion of the fibrils. Furthermore, the assembly process is shown to depend on the nanoscale morphology and flexibility of the PNFs. Stiff/straight PNFs with long persistence lengths (∼2 μm) align at the air–water interface, with anisotropy decreasing toward the center of the droplet as Marangoni flows increase entanglement toward the center. By contrast, flexible/curved PNFs with shorter persistence lengths (<100 nm) align more uniformly throughout the droplet, likely due to enhanced local entanglements. Straight PNFs pack tightly, forming smaller clusters with short intercluster distances, while curved PNFs form intricate, adaptable networks with larger characteristic distances and more varied structures.
Compared to native protein monomers, β-lactoglobulin amyloid fibrils (β-LAFs) produced through strong acidic and high thermal conditions possess unique nutritional, technological, and physicochemical attributes, but there is yet inadequate comprehensive information about the architecture, preparation, and characterization for their wide consumption. In this review, we summarize recent progress in the generation, characterization, and application of β-LAFs. A holistic viewpoint is adopted to provide an in-depth, critical, and readable document useful to a broad community in chemistry, food, material science, medical, and environmental sciences. β-LAFs, as emulsifying and gelling agents, possess tremendous potential in bioactive/drug delivery, tissue engineering, food packaging, antioxidant/antibacterial/antiviral materials, environmental applications, etc. In this review, we set: (i) to highlight structural, physicochemical, and techno-functional properties of β-LAFs alongside the critical factors in the protein fibrillation process, (ii) to tabulate a large number of characterization techniques to understand various properties of β-LAFs, (iii) to consolidate the most important and up-to-date information from the field of β-LAF applications (like chemistry, food, material science, medical, environmental, etc.); and to reflect these progresses in one, comprehensive study, (iv) and finally, to broadly reflect on the difficulties with application of β-LAFs.
Biominerals present in organisms are typically inorganic–organic hybrid materials with unique complex form, hierarchically ordered superstructures, and superior materials properties. Bio‐inspired polymer‐controlled crystallization approaches, aiming to transform the optimized designs and formation mechanisms lurking in biominerals to artificial systems, have been successfully applied to the synthesis of a wide range of inorganic materials. In order to avoid duplication with previous reviews, in this chapter we only focus on the new branches of polymer‐controlled crystallization for the design and preparation of functional inorganic materials with novel structures and improved resulting properties. For clear understanding of the interactions between added polymers and growing crystals and their mediation over the final crystal structures, some basic principles of crystallization involving classical and nonclassical pathways are first introduced. Emphasis will be laid on latest developments and important advances of bio‐inspired synthesis of various kinds of functional inorganic materials via polymer‐controlled crystallization. Their resulting improvements in different properties and potential applications in diverse fields of energy transformation and storage, catalysis, sensing, environmental management, (bio)medical science, and so on are subsequently discussed and highlighted. The challenges of current studies and prospects for future research about this new branch topic are finally suggested.
In this study beta-lactoglobulin solutions were processed with glass beads in an orbital shaker at high temperatures and low pH value to identify the effect of mechanical stressing and surfaces on amyloid aggregation kinetics. The information will provide a better understanding on how specific mechanical factors provide a nucleation supporting effect on the assembling of building blocks for a more efficient production of functional amyloid aggregates. Because aggregate morphologies vary at pH 2 (semiflexible) or pH 3.5 (worm-like), examination at both pH values gives information about their specific formation and stability characteristics. Different diameters of glass beads (20–1000 μm), and different shaking frequencies (0 - 280 min−1) were used to vary mechanical stress energy, which was quantified by CFD-DEM simulations. To investigate surface effects, the hydrophobicity and surface roughness of glass beads was altered by modification with stearic acid. Amyloid aggregates and bead surfaces were analysed by ThT-assay, AFM and ATR-FTIR.
Hydrophobic beads with high surface roughness affected the aggregation negatively. The use of non-hydrophobic beads increased the formation kinetics of fibrils but not of worm-like aggregates, although, both morphologies had a reduced mean length.
Biomimetic science has attracted great interest in the fields of chemistry, biology, materials science, and energy. Biomimetic mineralization is the process of synthesizing inorganic minerals under the control of organic molecules or biomolecules under mild conditions. Peptides are the motifs that constitute proteins, and can self-assemble into various hierarchical structures and show a high affinity for inorganic substances. Therefore, peptides can be used as building blocks for the synthesis of functional biomimetic materials. With the participation of peptides, the morphology, size, and composition of mineralized materials can be controlled precisely. Peptides not only provide well-defined templates for the nucleation and growth of inorganic nanomaterials but also have the potential to confer inorganic nanomaterials with high catalytic efficiency, selectivity, and biotherapeutic functions. In this review, we systematically summarize research progress in the formation mechanism, nanostructural manipulation, and applications of peptide-templated mineralized materials. These can further inspire researchers to design structurally complex and functionalized biomimetic materials with great promising applications.
The natural ability of many proteins to polymerize into highly structured filaments has been harnessed as scaffolds to align functional molecules in a diverse range of biomaterials. Protein-engineering methodologies also enable the structural and physical properties of filaments to be tailored for specific biomaterial applications through genetic engineering or filaments built from the ground up using advances in the computational prediction of protein folding and assembly. Using these approaches, protein filament-based biomaterials have been engineered to accelerate enzymatic catalysis, provide routes for the biomineralization of inorganic materials, facilitate energy production and transfer, and provide support for mammalian cells for tissue engineering. In this review, we describe how the unique structural and functional diversity in natural and computationally designed protein filaments can be harnessed in biomaterials. In addition, we detail applications of these protein assemblies as material scaffolds with a particular emphasis on applications that exploit unique properties of specific filaments. Through the diversity of protein filaments, the biomaterial engineer's toolbox contains many modular protein filaments that will likely be incorporated as the main structural component of future biomaterials.
Given the broad use of nanostructured crystalline titania films, an environmentally friendly and more sustainable synthesis route is highly desirable. Here, a water‐based, low‐temperature route is presented to synthesize nanostructured foam‐like crystalline titania films. A pearl necklace‐like nanostructure is introduced as tailored titania morphology via biotemplating with the use of the major bovine whey protein ß‐lactoglobulin (ß‐lg). It is shown that titania crystallization in a brookite‐anatase mixed phase is promoted via spray deposition at a comparatively low temperature of 120 °C. The obtained crystallites have an average grain size of (4.2 ± 0.3) nm. In situ grazing incidence small‐angle and wide‐angle X‐ray scattering (GISAXS/GIWAXS) are simultaneously performed to understand the kinetics of film formation and the templating role of ß‐lg during spray coating. In the ß‐lg:titania biohybrid composites, the crystal growth in semicrystalline titania clusters is sterically directed by the condensing ß‐lg biomatrix. Due to using spray coating, the green chemistry approach to titania‐based functional films can be scaled up on a large scale, which can potentially be used in photocatalytic processes or systems related to energy application.
Electrocatalysis offers great promise for water purification but is limited by low active area and high uncontrollability of electrocatalysts. To overcome these constraints, we propose hybrid bulk electrodes by synthesizing and binding Pd nanocatalyst (nano-Pd) to the electrodes via amyloid fibrils (AFs). The AFs template is effective for controlling the nucleation, growth, and assembly of nano-Pd on the electrode. In addition, the three-dimensional hierarchically porous nanostructure of AFs is beneficial for loading high-density nano-Pd with a large active area. The novel hybrid cathodes exhibit superior electroreduction performance for detoxification of hexavalent chromium (Cr6+), 4-chlorophenol, and trichloroacetic acid in wastewater and drinking water. This study provides a proof-of-concept design of AFs-templated nano-Pd-based hybrid electrode, which constitutes a paradigm shift in electrocatalytic water purification, and broadens the horizon of its potential engineered applications.
Herein we demonstrate a novel way of modifying the colloidal stability of proteins by the presence of hydrophobic molecules. A protein capable of self-assembly into protein nanofibrils (PNFs) is milled with a hydrophobic molecular material. Upon dissolution in acidic water followed by heating, the proteins are converted into PNFs containing hydrophobic dyes. When aqueous dispersions of such PNFs are heated, films are formed at the air–water interface. The films contain ordered, optically anisotropic domains, and the shape of the reaction vessel can influence the PNF packing. We demonstrate the generality of the process by employing PNFs derived from the three proteins bovine insulin (INS), β-lactoglobulin (BLG), and hen egg white lysozyme (HEWL) in combination with the dyes α-sexithiophene (6T) and 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM). As individual dye molecules are oriented along the long PNF axis, whole ensembles of dyes become aligned and, as a result, display emission of polarized light. Moreover, in the case of PNFs stained with DCM, stimulated emission is demonstrated.
Metal nanohybrids are fast emerging functional nanomaterials with advanced structures, intriguing physicochemical properties, and a broad range of important applications in current nanoscience research. Significant efforts have been devoted toward design and develop versatile metal nanohybrid systems. Among numerous biological components, diverse proteins offer avenues for making advanced multifunctional systems with unusual properties, desired functions, and potential applications. This review discusses the rational design, properties, and applications of metal-protein nanohybrid materials fabricated from proteins and inorganic components. The construction of functional biomimetic nanohybrid materials is first briefly introduced. The properties and functions of these hybrid materials are then discussed. After that, an overview of promising application of biomimetic metal-protein nanohybrid materials is provided. Finally, the key challenges and outlooks related to this fascinating research area are also outlined.
Fibrillar amyloids exhibit a fascinating range of mechanical, optical, and electronic properties originating from their characteristic β-sheet-rich structure. Harnessing these functionalities in practical applications has so far been hampered by a limited ability to control the amyloid self-assembly process at the macroscopic scale. Here, we use core-shell electrospinning with microconfinement to assemble amyloid-hybrid fibers, consisting of densely aggregated fibrillar amyloids stabilized by a polymer shell. Up to centimeter-long hybrid fibers with micrometer diameter can be arranged into aligned and ordered arrays and deposited onto substrates or produced as free-standing networks. Properties that are characteristic of amyloids, including their high elastic moduli and intrinsic fluorescence signature, are retained in the hybrid fiber cores, and we show that they fully persist through the macroscopic fiber patterns. Our findings suggest that microlevel confinement is key for the guided assembly of amyloids from monomeric proteins.
The past few decades have witnessed transition metal oxides (TMOs) as promising candidates for a plethora of applications in numerous fields. The exceptional properties retained by these materials have rendered them of paramount emphasis as functional materials. Thus, the controlled and scalable synthesis of transition metal oxides with desired properties has received enormous attention. Out of different top-down and bottom-up approaches, template-assisted synthesis predominates as an adept approach for the facile synthesis of transition metal oxides, owing to its phenomenal ability for morphological and physicochemical tuning. This review presents a comprehensive examination of the recent advances in the soft-template-assisted synthesis of TMOs, focusing on the morphological and physicochemical tuning aided by different soft-templates. The promising applications of TMOs are explained in detail, emphasizing those with excellent performances.
The origin of self‐winding mechanisms in plants’ tendrils has fascinated scientists for centuries and continues to inspire developments in material science and nanotechnology. Here, bioinspired water‐responsive wires that replicate these mechanisms, including the formation of coils and chiral perversions, are presented. A right‐handed gelatin matrix is loaded with rigid left‐handed amyloid fibrils and roll–dry‐spun into wires in which self‐winding activation emerges from simultaneous bending and twisting deformations. Wire bending is a consequence of amyloid fibrils’ concentration and distribution within the wire, whereas twisting is controlled by amyloid fibrils’ orientation. The resultant wires can be functionalized by organic molecules and inorganic nanoparticles, and potential applications in magnetic actuators and sensors are demonstrated. The simple fabrication method and the remarkable spontaneous self‐winding response of these gelatin–amyloid wires exemplify how biomaterials based on mixed proteins have striking potential to develop advanced and tunable properties that can serve robotics, soft machines, and engineering systems. A gelatin matrix is loaded with amyloid fibrils, similarly to fiber‐reinforced composites. This material is dry‐spun into wires with asymmetric core–shell cross‐sections that develop Young's modulus gradients. In water, these wires undergo differential swelling, causing spontaneous self‐winding, corresponding to climbing plants’ tendrils. The functionalization of amyloid fibrils enables the fabrication of functional wires with accurate sensing and actuation properties.
Amyloid diseases are global epidemics with profound health, social and economic implications and yet remain without a cure. This dire situation calls for research into the origin and pathological manifestations of amyloidosis to stimulate continued development of new therapeutics. In basic science and engineering, the cross-β architecture has been a constant thread underlying the structural characteristics of pathological and functional amyloids, and realizing that amyloid structures can be both pathological and functional in nature has fuelled innovations in artificial amyloids, whose use today ranges from water purification to 3D printing. At the conclusion of a half century since Eanes and Glenner’s seminal study of amyloids in humans, this review commemorates the occasion by documenting the major milestones in amyloid research to date, from the perspectives of structural biology, biophysics, medicine, microbiology, engineering and nanotechnology. We also discuss new challenges and opportunities to drive this interdisciplinary field moving forward.
Amyloids are associated with human disease. However, they are also exploited by nature for functional purposes. Functional amyloids have inspired amyloid-based biomaterials for different nanotechnologies. Early soluble species in the fibrillation pathway seem to be the primary elicitors of cytotoxicity, instead of fibrils. Organisms have evolved dedicated mechanisms to avoid toxicity during the assembly of functional amyloids. In their absence, artificial amyloid-based nanomaterials might also produce toxic intermediates. We show here that even when the building blocks of artificial amyloids are small, polar and compositionally simple, their early soluble assemblies are extremely cytotoxic, causing cell death through mechanisms identical to those of disease-associated proteins. Our results raise safety concerns about the use of non-natural amyloid-based materials without a rigorous characterization of their fibrillation pathway. Besides, the simple, cheap, and easy to synthesize peptides we use here might turn very useful to understand the molecular determinants behind amyloid cytotoxicity.
Marine mollusks have inspired to construct robust composites with hierarchical microstructures, and also to design artificial muscles with rapid and controllable deformation. Abalone nacre has the unique “brick and mortar” structure, whose two-dimensional (2D) “mortar” can serve both as the strong adhesive between aragonite platelets, and as the raw material for organic and carbon nanomeshes applicable in soft ionic actuator. Through an optimal production procedure, carbon nanomeshes with abundant micropores (0.7−2 nm) and in-plane mesopores (9−13 nm) are produced in high yield. When incorporating into the actuator electrodes, their large surface area (>625 m² g⁻¹) and heteroatom doping (>7.5 %) ensure to offer large ion storage desired by large deformation. Their in-plane mesopores allow for ion penetration desired by fast actuating kinetics, in contrast to graphene nanosheets which block free ion transportation. The resultant ionic actuator shows a low driving voltage (≤3 V), large deformation strain difference (1.11%), fast actuation (10⁰ s) and air working durability (>10⁴ cycles), being superior to the actuators based on other 2D carbon nanomaterials. Thus this low-cost and scalable production of carbon nanomeshes offers not only a novel type of biomass-based carbon nanomaterials, but also a high-performance electrochemical actuator applicable in soft robotics and smart devices.
Most of the biomolecules are chiral and this very aspect is often propagated and amplified through dynamic recognition processes to create macroscopic objects. In this chapter, we will focus on how chirality transfer is observed in various systems with different levels of complexity, particularly for the nanometric molecular self‐assemblies. We will then present our own studies in which the concept of chirality transfer is used at different levels, starting from a chiral molecule to functional materials with new chiral properties.
Effective and selective removal of fluoride from water systems is a pressing global issue for both drinking water and wastewater purification. Most of the present adsorbents exhibit inferior removal performance and low capacity, due to the intrinsic feature (light halogenide) of fluoride ions, so that developing new materials capable to remove both high and low concentrations of fluoride from water remains a challenge. This work reports a new strategy for efficient removal of fluoride from contaminated water streams, which relies on carbon hybrid membranes made of amyloid fibrils‐ZrO2 nanoparticles (<10 nm) nucleated in‐situ onto the amyloid fibrils surface via a chemical deposition process. These nanoparticles provide the ensued hybrids a remarkable affinity towards fluoride and very efficient removal performance when used in the form of membranes in combination with activated carbon to increase permeability. These hybrid membranes exhibit superior selectivity for fluoride against various competitive ions, with a distribution coefficient Kd as high as 6820 mL/g, exceeding commercial ion‐exchange resins (IRA‐900) by 180 times and outdoing the performance of most commercial carbon‐activated aluminum membranes. In both low (several mg/L) and highly (~200 mg/L) fluoride concentrations, representative of tap‐water and wastewater contamination regimes, the efficiency of the membrane exceeds 99.5% removal. Benchmark on real untreated municipal tap water (~2.8 mg/L) under continuous operating mode, indicates that ~1750 Kg water/m2 membrane can be treated while maintain water quality above WHO drinking threshold, and the saturated membranes can be regenerated and re‐used several times without decrease in performance. The selectivity of the membranes, their simple and affordable manufacturing and their high performance on real water sources, make this technology highly promising for mitigating the problem of fluoride water contamination worldwide
We report a new strategy for efficient removal of F⁻ from contaminated water streams, and it relies on carbon hybrid membranes made of amyloid fibril/ZrO2 nanoparticles (<10 nm). These membranes exhibit superior selectivity for F⁻ against various competitive ions, with a distribution coefficient (Kd) as high as 6820 mL g⁻¹, exceeding commercial ion‐exchange resins (IRA‐900) by 180 times and outdoing the performance of most commercial carbon‐activated aluminum membranes. At both low and high (ca. 200 mg L⁻¹) F⁻ concentrations, the membrane efficiency exceeds 99.5 % removal. For real untreated municipal tap water (ca. 2.8 mg L⁻¹) under continuous operating mode, data indicates that about 1750 kg water m⁻² membrane can be treated while maintaining drinking water quality, and the saturated membranes can be regenerated and reused several times without decrease in performance. This technology is promising for mitigating the problem of fluoride water contamination worldwide.
Bacterial type IV pili (T4P) are polymeric protein nanofibers that have diverse biological roles. Their unique physicochemical properties mark them as a candidate biomaterial for various applications, yet difficulties in producing native T4P hinder their utilization. Recent effort to mimic the T4P of the metal‐reducing Geobacter sulfurreducens bacterium led to the design of synthetic peptide building blocks, which self‐assemble into T4P‐like nanofibers. Here, it is reported that the T4P‐like peptide nanofibers efficiently bind metal oxide particles and reduce Au ions analogously to their native counterparts, and thus give rise to versatile and multifunctional peptide–metal nanocomposites. Focusing on the interaction with Au ions, a combination of experimental and computational methods provides mechanistic insight into the formation of an exceptionally dense Au nanoparticle (AuNP) decoration of the nanofibers. Characterization of the thus‐formed peptide–AuNPs nanocomposite reveals enhanced thermal stability, electrical conductivity from the single‐fiber level up, and substrate‐selective adhesion. Exploring its potential applications, it is demonstrated that the peptide–AuNPs nanocomposite can act as a reusable catalytic coating or form self‐supporting immersible films of desired shapes. The films scaffold the assembly of cardiac cells into synchronized patches, and present static charge detection capabilities at the macroscale. The study presents a novel T4P‐inspired biometallic material. Inspired by bacterial metal‐binding protein nanofibers, nanocomposites are fabricated from mimetic self‐assembled peptide nanofibers and metallic moieties. Experimental and computational methods show how reduction of ionic Au by the nanofibers leads to their exceptionally dense decoration by gold nanoparticles. The thus‐formed nanocomposite forms a catalytic coating, or immersible self‐supporting films for cardiac patch assembly and static charge detection.
Amyloids are highly ordered peptide/protein aggregates traditionally associated with multiple human diseases including neurodegenerative disorders. However, recent studies suggest that amyloids can also perform several biological functions in organisms varying from bacteria to mammals. In many lower organisms, amyloid fibrils function as adhesives due to their unique surface topography. Recently, amyloid fibrils have been shown to support attachment and spreading of mammalian cells by interacting with the cell membrane and by cell adhesion machinery activation. Moreover, similar to cellular responses on natural extracellular matrices (ECMs), mammalian cells on amyloid surfaces also use integrin machinery for spreading, migration, and differentiation. This has led to the development of biocompatible and implantable amyloid-based hydrogels that could induce lineage-specific differentiation of stem cells. In this chapter, based on adhesion of both lower organisms and mammalian cells on amyloid nanofibrils, we posit that amyloids could have functioned as a primitive extracellular matrix in primordial earth.
This thesis presents a systematic study of how different types monolayer-protected AuNPs interact with amyloid fibers. We report a class of amphiphilic gold nanoparticles capable of adsorbing onto specific surface features on these types of protein fibers. A common disease-associated protein fold is the amyloid state: it is characterized by a cross-beta sheet structure that forces proteins and peptides into a fibrillar state, commonly found in illnesses such as Alzheimerâs disease, Parkinsonâs disease among many others. Amyloid diseases are typically chronic, correlated with ageing and have posed several challenges: the exact structure of the fibers is difficult to determine and their etiologic role is often unclear. This thesis shows, for the first time, that amphiphilic monolayer-protected AuNPs can discriminatively adsorb onto surface features of amyloid fibers made of A1-40 and -synuclein in vitro and that hydrophobicity determines adsorption onto Tau fibers. Given an amyloid fiber that adopts a twisted ribbon morphology, AuNPs protected by a mixture of sulfonated and hydrophobic thiolate molecules adsorb onto specific features on the surface of the fiber, leaving other interfaces uncovered. This generates a novel supra-molecular assembly that directly interfaces an engineered nanomaterial with a biological structure, without using antibodies. Experiments and calculations demonstrated the importance of nanoparticle size and ligand-shell composition: a size cut-off around 4 nm was observed and other types of water soluble nanoparticles did not adsorb discriminatively. Small amphiphilic AuNPs act as surfactants and probably adsorb onto solvent-exposed beta sheets and small amyloidogenic oligomers. The results presented in this thesis provide a systematic framework to understand the interaction between nanoparticles and amyloid fibers. The particles can, moreover, become useful markers for amyloid research and possibly a cross-instrumental probe to reconcile spectroscopic and imaging techniques to help molecular structure determination. During this work, the synthesis and purification of large amounts of sulfonated thiolate molecules was systematized to generate libraries of differently coated water soluble gold nanoparticles (AuNPs). This helped elucidate how amphiphilic AuNPs fuse with lipid bilayers.
The formation of elongated supra-molecular structures from protein building blocks generates functional intracellular filaments, but this process is also at the heart of many neurodegenerative conditions including Alzheimer’s and Parkinson’s diseases, where it occurs in an uncontrolled manner. When observed at appropriate concentration and time scales, the chemical kinetics of filamentous protein self-assembly exhibits the remarkable property of self-similarity: the dynamics appears similar as the observation scale changes. We discuss here how this property leads to crucial simplifications of the fundamental laws governing protein filament formation and the emergence of scaling laws that provide the basis for connecting microscopic events with macroscopic realisations of such processes. In particular, we review recent developments in the modelling of linear protein self-assembly phenomena in the light of the concepts of dimensional analysis and physical self-similarity. We show how these tools and concepts can be used to elucidate the nature of the scaling laws for filamentous protein self-assembly, which illuminate the ultimately simple mathematical and physical principles underlying this seemingly highly complex phenomenon, and are expected to guide further developments in the field of linear self-assembly.
Amyloid nanowires were incorporated in organic photovoltaic devices in order to enhance the transport properties. Amyloid fibrils act as a template for donor-acceptor materials. The current-voltage characteristics under illumination and in the dark display a maximum for the fill factor and the space charge limit current, respectively, at an amyloid nanowire-donor-acceptor mass ratio of 0.014:1:1, associated to a better charge transport in the donor-acceptor domains. The absorption experiments display a redshift associated to a more planar polymer backbone with increasing concentration of amyloid fibrils. Amyloid nanowires present a significant effect on the donor-acceptor materials organization.
Vertically aligned Ti O 2 nanorods were prepared by its sol-gel which is spun coat onto aluminum anodic oxide template pregrown on an indium tin oxide glass substrate. The poly(3-hexylthiophene) (P3HT), a conjugate polymer infiltrated into the nanorod arrays, and the combined system were used as the active layer. The nanorods/P3HT solar cell with cell size of 0.06 cm 2 demonstrated a power conversion efficiency of 0.512% while the bilayer Ti O 2 film/P3HT cell was 0.12%. The current work provides fabrication method for a stable well aligned nanorods/polymer hybrid solar cell production.
Amyloid fibrils belong to the group of ordered nanostructures that are self-assembled from a wide range of polypeptides/proteins. Amyloids are highly rigid structures possessing a high mechanical strength. Although amyloids have been implicated in the pathogenesis of several human diseases, growing evidence indicates that amyloids may also perform native functions in host organisms. Discovery of such amyloids, referred to as functional amyloids, highlight their possible use in designing novel nanostructure materials. This review summarizes recent advances in the application of amyloids for the development of nanomaterials and prospective applications of such materials in nanotechnology and biomedicine.
The aggregation of proteins is central to many aspects of daily life, including food processing, blood coagulation, eye cataract formation disease and prion-related neurodegenerative infections. However, the physical mechanisms responsible for amyloidosis-the irreversible fibril formation of various proteins that is linked to disorders such as Alzheimer's, Creutzfeldt-Jakob and Huntington's diseases-have not yet been fully elucidated. Here, we show that different stages of amyloid aggregation can be examined by performing a statistical polymer physics analysis of single-molecule atomic force microscopy images of heat-denatured beta-lactoglobulin fibrils. The atomic force microscopy analysis, supported by theoretical arguments, reveals that the fibrils have a multistranded helical shape with twisted ribbon-like structures. Our results also indicate a possible general model for amyloid fibril assembly and illustrate the potential of this approach for investigating fibrillar systems.
Focusing on the basic principles of mineral formation by organisms, this comprehensive volume explores questions that relate to a wide variety of fields, from biology and biochemistry, to paleontology, geology, and medical research. Preserved fossils are used to date geological deposits and archaeological artifacts. Materials scientists investigate mineralized tissues to determine the design principles used by organisms to form strong materials. Many medical problems are also associated with normal and pathological mineralization. Lowenstam, the pioneer researcher in biomineralization, and Weiner discuss the basic principles of mineral formation by organisms and compare various mineralization processes. Reference tables listing all known cases in which organisms form minerals are included.
We have investigated the structural time-evolution of multistranded β-lactoglobulinproteinfibrils at pH 2 and 90 °C by combining small angle neutron scattering (SANS), dynamic (DLS) and depolarized light scattering (DDLS) as well as atomic force microscopy (AFM). Light scattering techniques, combined with SANS clearly demonstrate the different stages of conversion of β-lactoglobulin monomers (2 wt %) into semiflexible proteinfibrils upon heating at 90 °C. In addition, atomic force microscopy allows the resolution of some details of the fibrils at the molecular length scale which bulk scattering techniques cannot capture. Thus, we were able to resolve and identify different individual stages of the fibrillation process, including the formation of protofilaments, their alignment and aggregation into mature multistranded fibrils, and the development of a periodic pitch along their contour length. The picture emerging from combination of the scattering and single molecule techniques is consistent with three critical steps: (i) individual protofilaments align upon approaching due to liquid crystalline interactions; (ii) short range attractions among filaments—presumably of Lennard–Jones or hydrophobicity type—lead to irreversible aggregation of nearly perfectly aligned protofilaments into multistranded ribbon-like fibrils; (iii) intramolecular electrostatic repulsion of fibrils leads to twisting of the ribbon along the axis leading to the development of a periodic pitch along the fibrils contour length. The individual stages of the fibrillation and aggregation process are discussed in detail, in terms of the colloidal physics involved.
Titania (TiO2) nanoparticles are widely used, or are under active development, for a range of applications in (photo)catalysis, photovoltaics, enzyme support, energy storage, and photonics. The peptide-directed room-temperature formation of titania nanoparticles can be an attractive alternative to higher-temperature synthetic methods. However, the influence of the peptide primary structure on the titania precipitation activity at room temperature is not well understood. Through the selective binding of phage-displayed 12-mer peptides to TiO2 substrates, we have identified 20 peptides with an affinity for titania. The average numbers of arginine, lysine, and histidine residues present in these 20 peptides were distinctly higher than for the overall peptide-bearing phage library. Synthetic 16-mer versions of four of these peptides (i.e., 12-mer peptides with C-terminal tetrapeptide tags for quantitative spectrophotometry) induced the formation of 8.1–38.7 mol TiO2/mol peptide after exposure for only 10 min to an otherwise water-stable Ti(IV) complex at room temperature and a pH of 6.3. X-ray diffraction analyses, electron diffraction analyses, and high-resolution transmission electron microscopy revealed that the peptide-induced titania contained fine (<10 nm) anatase and monoclinic β-TiO2 nanocrystals, along with an amorphous phase. The titania yield increased with the number of positive charges carried by these peptides. On the basis of these results, a peptide was designed that exhibited the highest titania formation activity reported to date for a peptide (82.9 mol TiO2/mol peptide), as well as a reduced pH dependence for such titania formation.
We report the characteristics of polymer∕nanocrystalline solar cells fabricated using an environmentally friendly water-soluble polythiophene and TiO2 in a bilayer configuration. The cells were made by dropping the polymer onto a TiO2 nanocrystalline film and then repeatedly sweeping a clean glass rod across the polymer as it dried. The devices showed an open circuit voltage of 0.81 V, a short circuit current density of 0.35 mA/cm2, a fill factor of 0.4, and an energy conversion efficiency of 0.13%. The water-soluble polythiophene showed significant photovoltaic behavior and the potential for use in solar cells.
Poly(allylamine) (a mimic of biopolyamines) and the R5 peptide (a repeat unit of a silaffin protein isolated from a diatom) induce the formation of mineralized titanium from soluble titanium(IV) precursors. These reactions proceed under mild aqueous conditions. Scanning electron microscopy shows that the nanometer to micrometer diameter particles induced by poly(allylamine) are spherical under a range of conditions, while those induced by the R5 peptide include spheres and fused structures. Dynamic light scattering experiments confirm the SEM results and reveal that the particles range in size from 2 nm to 5 μm. The surface charge is negative at neutral pH. Energy dispersive X-ray spectroscopy shows the composition to be primarily titanium, oxygen, and phosphorus. The solids are amorphous at room temperature by powder X-ray diffraction but the material induced by poly(allylamine) converts to cubic crystalline TiP2O7 with annealing to 800 °C. Infrared spectroscopy suggests that the biomolecule mineralization inducers are encapsulated in the solid. Discrete poly(allylamine)-induced spheres are formed only between pH 7−9.5, with polydispersity strongly dependent on pH. The surface of the poly(allylamine)-induced spheres becomes smoother at higher reaction temperatures. Green fluorescent protein can be immobilized in the solid induced by poly(allylamine) but not R5 peptide under the conditions examined.
Current approaches to the synthesis of metal oxides generally require harsh conditions. In contrast, many biological processes can produce intricate metal oxide nanostructures under ambient conditions. For example, the diatom Cylindrotheca fusiformis forms reproducible nanostructures from silicic acid using species specific peptides known as silaffins. Herein, we report that the R5 peptide a bioinspired analogue derived from the NatSil protein in C. fusiformis can form titanium dioxide (TiO2) in a concentration dependent manner from the non-natural substrate, titanium bis(ammonium lactato)dihydroxide. Additionally, the polypeptide poly(l-lysine) acts as a template for the biomimetic synthesis of TiO2. Subsequently, the nanoparticles were characterized using scanning electron microscopy, energy-dispersive X-ray spectrometry, and IR spectroscopy. A variable temperature X-ray diffraction study of the titanium dioxide phase transition from anatase to rutile was conducted. A delay in transition temperature was observed with titanium dioxide synthesized in the presence of phosphate buffer.
Silicatein, an enzymatic biocatalyst purified from the glassy skeletal elements of a marine sponge, and previously shown capable of catalyzing and structurally directing the hydrolysis and polycondensation of silicon alkoxides to yield silica and silsesquioxanes at low temperature and pressure and neutral pH, is shown to be capable of catalyzing and templating the hydrolysis and subsequent polycondensation of a water-stable alkoxide-like conjugate of titanium to form titanium dioxide. The structure and behavior of the TiO2 formed through this biocatalytic route, including thermally induced crystal grain growth and phase transformation from anatase to rutile, differ from those of TiO2 formed from the same precursor via alkali catalysis or thermal pyrolysis. This enzymatic route affords a path to templated synthesis that avoids the high temperatures and extremes of pH typically required for synthesis of metallo-oxanes from the corresponding alkoxide-like precursors, and thus provides access to a new and potentially useful parameter space of structures and properties. The proteins may also be nanoscopically structure-directing, as evidenced by the formation of nanocrystallites of anatase, a polymorph usually formed at much higher temperatures. The summation of weak interactions between the protein and mineral may induce this stabilization and thus may afford a new level of nanostructural control, with associated enhancement of selected performance properties.
We have made photovoltaic cells by infiltrating the conjugated polymer regioregular poly(3-hexylthiophene) into films of mesoporous titania, which are self-assembled using a structure directing block copolymer. The mesoporous titania films were chosen because they have pores with a diameter slightly less than 10 nm, which is the exciton diffusion length in many conjugated polymers, and because they provide continuous pathways for electrons to travel to an electrode after electron transfer has occurred. The photovoltaic cells have an external quantum efficiency of 10% and a 1.5% power conversion efficiency under monochromatic 514 nm light. Experiments that vary the amount of polymer in the titania films suggest that the performance of the cells is limited by poor hole transport in the polymer. © 2003 American Institute of Physics.
Amyloid or amyloid-like fibrils represent a general class of nanomaterials that can be formed from many different peptides and proteins. Although these structures have an important role in neurodegenerative disorders, amyloid materials have also been exploited for functional purposes by organisms ranging from bacteria to mammals. Here we review the functional and pathological roles of amyloid materials and discuss how they can be linked back to their nanoscale origins in the structure and nanomechanics of these materials. We focus on insights both from experiments and simulations, and discuss how comparisons between functional protein filaments and structures that are assembled abnormally can shed light on the fundamental material selection criteria that lead to evolutionary bias in multiscale material design in nature.
Fibrils of β-lactoglobulin, formed by heating at pH 2, were titrated with a sulfated polysaccharide (κ-carrageenan) to determine the morphology and mechanism of complex formation at low pH. Structural information on the resultant complexes was gathered using transmission electron microscopy, atomic force microscopy, Doppler electrophoresis, and small-angle neutron scattering. Electrophoresis demonstrated that the carrageenan complexed with protein fibrils until reaching a maximum complexation efficiency at a protein/polysaccharide (r) weight ratio of 5:3. Neutron scattering and microscopy indicated an increasing formation of spherical aggregates attached along the protein fibrils with increases in the carrageenan concentration. These globular particles had an average diameter of 30 nm. Small-angle neutron scattering of these complexes could be accurately described by a form factor corresponding to multistranded twisted ribbons with spherical aggregates along their contour length, arranged in a necklace configuration.
We report for the first time on the templating effect of β-lactoglobulin amyloid-like fibrils to synthesize gold single crystals of several decades of μm in dimensions. The gold single crystals were produced by reducing an aqueous solution of chloroauric acid by β-lactoglobulin amyloid protein fibrils. Atomic force microscopy, conventional and scanning transmission electron microscopy, electron diffraction and optical microscopy techniques were combined to characterize the structure of the gold crystals. The single-crystalline features of these macroscopic gold crystals are witnessed by their distinctive hexagonal and triangular shape and are confirmed by selected area electron diffraction (SAED). UV-vis absorption spectrum, recorded after a reaction time of 6h at the heating temperature of 55°C showed a surface plasmon resonance peak at 540 nm. With the increase of reaction time to 24h, the absorption spectrum peaks shift to a very broad and higher wavelength region extending up to near infrared region. Remarkably, these single crystalline gold crystals show auto fluorescence when illuminated to UV lamp. Further increase in β-lactoglobulin amyloid fibrils concentration above the isotropic-nematic transition, drives the formation of gold single crystals microplates stacking together and self-assembling into new hierarchical, layered protein-gold hybrid composites.
Biomineralization is a hot topic in the area of materials, and this volume in the Metals Ions in Life Sciences series takes a systematic approach, dealing with all aspects from the fundamentals to applications. Key biological features of biomineralization, such as gene directed growth and the role of enzymes are covered, as are new areas, including copper/zinc in the jaws of invertebrates or magnetic biomaterials that help birds with navigation.
We are entering a new phase in biomaterials research in which rational design is being used to produce functionalised materials tailored to specific applications. As is evident from this Themed Issue, there are now a number of distinct types of designed, self-assembling, fibrous biomaterials. Many of these are ripe for development and application for example as scaffolds for 3D cell culture and tissue engineering, and in templating inorganic materials. Whilst a number of groups are making headway towards such applications, there is a general challenge to translate a wealth of excellent basic research into materials with a genuine future in real-life applications. Amongst other contemporary aspects of this evolving research area, a key issue is that of decorating or functionalising what are mostly bare scaffolds. There are a number of hurdles to overcome to achieve effective and controlled labelling of the scaffolds, for instance: maintaining biocompatibility, i.e., by minimising covalent chemistry, or using milder bioconjugation methods; attaining specified levels of decoration, and, in particular, high and stoichiometric labelling; introducing orthogonality, such that two or more functions can be appended to the same scaffold; and, in relevant cases, maintaining the possibility for recombinant peptide/protein production. In this critical review, we present an overview of the different approaches to tackling these challenges largely for self-assembled, peptide-based fibrous systems. We review the field as it stands by placing work within general routes to fibre functionalisation; give worked examples on our own specific system, the SAFs; and explore the potential for future developments in the area. Our feeling is that by tackling the challenges of designing multi-component and functional biomaterials, as a community we stand to learn a great deal about self-assembling biomolecular systems more broadly, as well as, hopefully, delivering new materials that will be truly useful in biotechnology and biomedical applications (107 references).
The fabrication of biomaterials which serve as functional scaffolds exhibiting diversified effects has been valued. We report here a unique strategy to fibrillate hemoglobin A (HbA), which exhibits multiple photoelectrochemical properties, and a subsequent specific defibrillation procedure. A subtle structural rearrangement of the α/β-subunits within the quaternary structure of HbA is responsible for the HbA fibril formation in the presence of 0.5% CHCl₃. The narrow pH dependence of the suprastructure formation around pH 7.4 illustrates the highly sensitive nature of the structural alteration. The CHCl₃-induced fibrils become disintegrated by ascorbic acid, indicating that the oxidation-reduction process of the iron within the heme moiety could be involved in stabilization of the fibrillar structures. The electron-transferring property of the iron allows the fibrils to exhibit not only their conductive behavior but also a photodynamic effect generating hydroxyl radicals in the presence of H(2)O(2) with light illumination. A photovoltaic effect is also demonstrated with the HbA fibrils, which generate an electric current on the fibril-coated microelectrode upon irradiation at 405nm. Taken together, the multiple effects of HbA fibrils and the selective fibrillation/defibrillation procedures could qualify the fibrils to be employed for various future applications in biotechnology, including bio-machine interfaces.
We have developed a new method allowing the study of the thermodynamic phase behavior of mesoscopic colloidal systems consisting of amyloid protein fibers in water, obtained by heat denaturation and aggregation of beta-lactoglobulin, a dairy protein. The fibers have a cross section of about 5.2 nm and two groups of polydisperse contour lengths: (i) long fibers of 1-20 microm, showing semiflexible behavior, and (ii) short rods of 100-200 nm long, obtained by cutting the long fibers via high-pressure homogenization. At pH 2 without salt, these fibers are highly charged and stable in water. We have studied the isotropic-nematic phase transition for both systems and compared our results with the theoretical values predicted by Onsager's theory. The experimentally measured isotropic-nematic phase transition was found to occur at 0.4% and at 3% for the long and short fibers, respectively. For both systems, this phase transition occurs at concentrations more than 1 order of magnitude lower than what is expected based on Onsager's theory. Moreover, at low enough pH, no intermediate biphasic region was observed between the isotropic phase and the nematic phase. The phase diagrams of both systems (pH vs concentration) showed similar, yet complex and rich, phase behavior. We discuss the possible physical fundamentals ruling the phase diagram as well as the discrepancy we observe for the isotropic-nematic phase transition between our experimental results and the predicted theoretical results. Our work highlights that systems formed by water-amyloid protein fibers are way too complex to be understood based solely on Onsager's theories. Experimental results are revisited in terms of the Flory's theory (1956) for suspensions of rods, which allows accounting for rod-solvent hydrophobic interactions. This theoretical approach allows explaining, on a semiquantitative basis, most of the discrepancies observed between the experimental results and Onsager's predictions. The sources of protein fibers complex colloidal behavior are analyzed and discussed at length.
Yeast-derived peptides, zinc fingerlike peptides, protein cages, engineered dendritic and amphiphilic peptides, phage-displayed library-identified peptides, and commercially available proteins have all been utilized to produce semiconductor nanoparticles with varying degrees of success. A select number of these biomolecules have synthesized quantum-confined semiconductors with size distributions equal to or finer than those achieved with the most modern synthetic techniques, while avoiding the use of exotic organic solvents and high temperatures. The chemistry and crystal structure (polymorph) control achieved through biomimetic mineralization is also notable. While such biomolecule-controlled syntheses of semiconductor nanomaterials have been achieved, further advances rivaling or exceeding synthetic approaches seem possible and likely. For example, one particular area in which biomimetic engineering may make inroads relative to synthetic chemistry is in the production of core-shell or hybrid quantum structures, wherein protein or peptide templates can be used to direct/ template the growth of several semiconductor materials.
We report on the conformation of heat-induced bovine beta-lactoglobulin (betalg) aggregates prepared at different pH conditions, and their complexes with model anionic surfactants such as sodium dodecyl sulfate (SDS). The investigation was carried out by combining a wide range of techniques such as ultra small angle light scattering, static and dynamic light scattering, small angle neutron scattering, small-angle X-ray scattering, electrophoretic mobility, isothermal titration calorimetry (ITC) and transmission electron microscopy. Three types of aggregates were generated upon heating betalg aqueous dispersions at increasing pH from 2.0 to 5.8 to 7.0: rod-like aggregates, spherical aggregates, and worm-like primary aggregates, respectively. These aggregates were shown not only to differ for their sizes and morphologies, but also for their internal structures and fractal dimensions. The main differences between aggregates are discussed in terms of the ionic charge and conformational changes arising for betalg at different pHs. The formation of complexes between SDS and the various protein aggregates at pH 3.0 was shown to occur by two main mechanisms: at low concentration of SDS, the complex formation occurs essentially by ionic binding between the positive residues of the protein and the negative sulfate heads of the surfactant. At complete neutralization of charges, precipitation of the complexes is observed. Upon further increase in SDS concentration, complex formation of SDS and the protein aggregates occurs primarily by hydrophobic interactions, leading to (i) the formation of an SDS double layer around the protein aggregates, (ii) the inversion of the total ionic charge of each individual protein aggregate, and (iii) the complete redispersion of the protein aggregate-SDS complexes in water. Remarkably, the SDS double layer around the protein aggregates provides an efficient protective shield, preventing precipitation of the aggregates at any possible pH values, including those values corresponding to the isoelectric pH of the aggregates.
We demonstrate that semiconductor nanorods can be used to fabricate readily processed and efficient hybrid solar cells together with polymers. By controlling nanorod length, we can change the distance on which electrons are transported directly through the thin film device. Tuning the band gap by altering the nanorod radius enabled us to optimize the overlap between the absorption spectrum of the cell and the solar emission spectrum. A photovoltaic device consisting of 7-nanometer by 60-nanometer CdSe nanorods and the conjugated polymer poly-3(hexylthiophene) was assembled from solution with an external quantum efficiency of over 54% and a monochromatic power conversion efficiency of 6.9% under 0.1 milliwatt per square centimeter illumination at 515 nanometers. Under Air Mass (A.M.) 1.5 Global solar conditions, we obtained a power conversion efficiency of 1.7%.
(Chemical Equation Presented) Biomineral-forming organisms provide inspiration for developing new reaction pathways to functional materials, such as rutile for optical devices. A recombinant protein (rSilC) was designed based on the sequence of a silica-forming protein from a diatom. This unique protein induced the formation of hierarchically nanostructured rutile microcrystals under mild reaction conditions (see SEM image).
The synthesis of supramolecular conducting nanowires can be achieved by using DNA and pyrrole. Oxidation of pyrrole in DNA-containing solutions yields a material that contains both the cationic polypyrrole (PPy) and the anionic DNA polymers. Intimate interaction of the two polymer chains in the self-assembled nanowires is indicated by FTIR spectroscopy. AFM imaging shows individual nanowires to be continuous, approximately 5 nm high and conformationally flexible. This feature allows them to be aligned by molecular combing in a similar manner to bare DNA and provides a convenient method for fabricating a simple electrical device by stretching DNA/PPy strands across an electrode gap. Current-voltage measurements confirm that the nanowires are conducting, with values typical for a polypyrrole-based material. In contrast to polymerisation of pyrrole on a DNA template in bulk solution, attempts to form similar wires by polymerisation at surface-immobilised DNA do not give a continuous coverage; instead, a beads-on-a-string appearance is observed suggesting that immobilisation inhibits the assembly process.
Naturally occurring polyamines putrescine, cadaverine, spermidine, and spermine are analogues of the species-specific long-chain polyamines found in diatoms. Scanning electron microscopy and energy-dispersive spectroscopy show that the reactions of a soluble Ti(IV) precursor with spermidine and spermine, but not putrescine or cadaverine, produce nanostructured irregular polyhedra of titanium oxide. At 25 degrees C, the average size of the particles formed with spermidine is 400 +/- 150 nm, and with spermine, 140 +/- 50 nm. Although the particles are X-ray amorphous at room temperature, annealing studies reveal that the particles adopt crystallinity at higher temperatures characteristic of anatase (TiO2). The major portion of the biopolyamines is not coprecipitated with the solid but is left in solution. Kinetic measurements reveal an initial fast step followed by two slower phases of reaction. At 25 degrees C, k(1obs) and k(2obs) for the reaction with spermidine are 5 x 10(-3) s(-1) and 3.6 x 10(-4) s(-1), respectively, and for spermine, 4.8 x 10(-3) s(-1) and 4.2 x 10(-4) s(-1), respectively. Taken together, the data suggest spermidine and spermine are biocatalysts for the precipitation of nanostructured titanium oxide.
Over the past decades, the tremendous effort put into TiO2 nanomaterials has resulted in a rich database for their synthesis, properties, modifications, and applications. The continuing breakthroughs in the synthesis and modifications of TiO2 nanomaterials have brought new properties and new applications with improved performance. Accompanied by the progress in the synthesis of TiO2 nanoparticles are new findings in the synthesis of TiO2 nanorods, nanotubes, nanowires, as well as mesoporous and photonic structures. Besides the well-know quantum-confinement effect, these new nanomaterials demonstrate size-dependent as well as shape- and structure-dependent optical, electronic, thermal, and structural properties. TiO2 nanomaterials have continued to be highly active in photocatalytic and photovoltaic applications, and they also demonstrate new applications including electrochromics, sensing, and hydrogen storage. This steady progress has demonstrated that TiO2 nanomaterials are playing and will continue to play an important role in the protections of the environment and in the search for renewable and clean energy technologies.
Amyloid fibers constitute one of the most abundant and important naturally occurring self-associated assemblies. A variety of protein and peptide molecules with various amino acid sequences form these highly stable and well-organized assemblies under diverse conditions. These assemblies display phase states ranging from liquid crystals to rigid nanotubes. The potential applications of these supramolecular assemblies exceed those of synthetic polymers since the building blocks may introduce biological function in addition to mechanical properties. Here we review the structural characteristics of amyloidal supramolecular assemblies, their potential use as either natural or de novo designed sequences, and the range of applications that have been demonstrated so far.
Proteins offer an almost infinite number of functions and geometries for building nanostructures. Here we have focused on amyloid fibrillar proteins as a nanowire template and shown that these fibrils can be coated with the highly conducting polymer alkoxysulfonate PEDOT through molecular self-assembly in water. Transmission electron microscopy and atomic force microscopy show that the coated fibers have a diameter around 15 nm and a length/thickness aspect ratio >1:1000 . We have further shown that networks of the conducting nanowires are electrically and electrochemically active by constructing fully functional electrochemical transistors with nanowire networks, operating at low voltages between 0 and 0.5 V.