Meital Reches

Low-Cost Printing of Poly(dimethylsiloxane) Barriers To Define Microchannels in Paper

This paper describes the use of a modified x,y-plotter to generate hydrophilic channels by printing a solution of hydrophobic polymer (pol(dimethylsiloxane; PDMS) dissolved in hexanes onto filter paper. The PDMS penetrates the depth of the paper and forms a hydrophobic wall that aqueous solutions cannot cross. The minimum size of printed features is approximately 1 mm; this resolution is adequate for the rapid prototyping of hand-held, visually read, diagnostic assays (and other microfluidic systems) based on paper. After curing the printed PDMS, the paper-based devices can be bent or folded to generate three-dimensional systems of channels. Capillary action pulls aqueous samples into the paper channels. Colorimetric assays for the presence of glucose and protein are demonstrated in the printed devices; spots of Bromothymol Blue distinguished samples with slightly basic pH (8.0) from samples with slightly acidic pH (6.5). The work also describes using printed devices that can be loaded using multipipets and printed flexible, foldable channels in paper over areas larger than 100 cm2.

Controlled patterning of aligned self-assembled peptide nanotubes.

Controlling the spatial organization of objects at the nanoscale is a key challenge in enabling their technological application1,2,3. Biomolecular assemblies are attractive nanostructures owing to their biocompatibility, straightforward chemical modifiability, inherent molecular recognition properties and their availability for bottom-up fabrication4,5,6,7,8,9,10,11,12,13,14,15,16. Aromatic peptide nanotubes are self-assembled nanostructures with unique physical and chemical stability and remarkable mechanical rigidity14,15,16. Their application in the fabrication of metallic nanowires and in the improvement of the sensitivity of electrochemical biosensors have already been demonstrated14,15,16,17. Here we show the formation of a vertically aligned nanoforest by axial unidirectional growth of a dense array of these peptide tubes. We also achieved horizontal alignment of the tubes through noncovalent coating of the tubes with a ferrofluid and the application of an external magnetic field. Taken together, our results demonstrate the ability to form a two-dimensional dense array of nanotube assemblies with either vertical or horizontal patterns.

Amyloid Fibril Formation by Pentapeptide and Tetrapeptide Fragments of Human Calcitonin

The process of amyloid fibril formation by the human calcitonin hormone is associated with medullary thyroid carcinoma. Based on the effect of pH on the fibrillization of human calcitonin, the analysis of conformationally constrained analogues of the hormone, and our suggestion regarding the role of aromatic residues in the process of amyloid fibril formation, we studied the ability of a short aromatic charged peptide fragment of calcitonin (NH2-DFNKF-COOH) to form amyloid fibrils. Here, using structural and biophysical analysis, we clearly demonstrate the ability of this short peptide to form well ordered amyloid fibrils. A shorter truncated tetrapeptide, NH2-DFNK-COOH, also formed fibrils albeit less ordered than those formed by the pentapeptide. We could not detect amyloid fibril formation by the NH2-FNKF-COOH tetrapeptide, the NH2-DFN-COOH tripeptide, or the NH2-DANKA-COOH phenylalanine to the alanine analogue of the pentapeptide. The formation of amyloid fibrils by rather hydrophilic peptides is quite striking, because it was speculated that hydrophobic interactions might play a key role in amyloid formation. This is the first reported case of fibril formation by a peptide as short as a tetrapeptide and one of very few cases of amyloid formation by pentapeptides. Because the aromatic nature seems to be the only common property of the various very short amyloid-forming peptides, it further supports our hypothesis on the role of aromatic interactions in the process of amyloid fibril formation.

Designed aromatic homo-dipeptides: formation of ordered nanostructures and potential nanotechnological applications

Molecular self-assembly offers new routes for the fabrication of novel materials at the nano-scale. Peptide-based nanostructures represent nano-objects of particular interest, as they are biocompatible, can be easily synthesized in large amounts, can be decorated with functional elements and can be used in various biological and non-biological applications. We had previously revealed the formation of highly ordered tubular structures by the diphenylalanine peptide, the core recognition motif of Alzheimers beta-amyloid polypeptide, due to specific aromatic interactions. We further confirmed this model and demonstrated that a non-charged peptide analogue, Ac-Phe-Phe-NH2, self-assembled into similar tubular structures. We later explored other amine and carboxyl modified diphenylalanine peptide analogues and revealed that these dipeptides can form ordered tubular structures at the nanometric scale. Moreover, a very similar peptide, the diphenylglycine, self-assembled into ordered nano-spherical assemblies. Here we extend our research and explore the self-assembly of other homo-aromatic dipeptides in which their phenyl side-chains are modified with halogen atoms (di-para-fluoro-Phe, di-pentafluoro-Phe, di-para-iodo-Phe), additional phenyl groups (di-4-phenyl-Phe), or with nitro substitutions (di-para-nitro-Phe). We also probed the effect of the alteration of the phenyl groups with naphtyl groups (di-D-1-Nal and di-D-2-Nal). In all cases, well-ordered nanostructures were obtained and studied by scanning electron microscopy, transmission electron microscopy and vibrational spectroscopy. Taken together, the current work and previous ones define the homo-aromatic dipeptide as a central motif for the formation of ordered self-assembled tubular, spherical and two-dimensional structures at the nano-scale.

Molecular Self-Assembly of Peptide Nanostructures: Mechanism of Association and Potential Uses

Molecular self-assembly offers unique directions for the fabrication of novel supramolecular structures and advanced materials. The inspiration for the development of such structures is often derived from self-assembling modules in biology, as natural systems form complex structures from simple building blocks such as amino acids, nucleic acids and lipids. Peptide-based nanostructures indicate an important route toward the production of ordered nanostructures as several studies had demonstrated their ability to form well organized assemblies. This includes cyclic peptides designed with alternating Dand Lamino acids, amphiphile peptides, peptide-conjugates and ionic self-complementary peptides. A naturally occurring self-assembly process of nano scale objects by polypeptides is that of amyloid fibril formation. These 7-10 nm fibrillar assemblies were already used for the formation of conductive nanowires. Short peptides have been used as model systems to study the molecular mechanism that leads to amyloid fibril formation. Based on the analysis of short amyloid forming fragments, it was recently suggested by our group and others that aromatic interactions may play a significant role in the process of amyloid fibrils formation in several cases. This hypothesis led to the discovery that the core recognition motif of the Alzheimer’s β-amyloid polypeptide, the diphenylalanine element, has all the molecular information needed to self assemble into a novel class of peptide nanotubes. A highly similar analog and the simplest aromatic dipeptide, the diphenylglycine, forms spherical nanometric assemblies. Both designed and peptide fragment nanostructures were suggested to have many applications in various fields including molecular electronics, tissue engineering, and material science. Biography: Meital Reches received her B.Sc. in Biology from Tel Aviv University in 2002. She joined Prof. Ehud Gazit research group at the Department of Molecular Microbiology and Biotechnology already as an undergraduate student and continued her graduate studies under his guidance in 2002. Her Ph.D. thesis focuses on self assembly of short peptides into superamolecular structures. She was awarded with the Dan David Scholarship for outstanding doctoral students and the Clore Foundation Program Doctoral

Self‐assembly of peptide nanotubes and amyloid‐like structures by charged‐termini‐capped diphenylalanine peptide analogues

We had recently demonstrated that the diphenylalanine peptide, the core recognition motif of the Alzheimers s-amyloid polypeptide, self-assembles into a novel class of peptide nanotubes. The formation of well-ordered supramolecular structures at the nanoscale by such a simple peptide was consistent with our suggestion that aromatic interactions may provide order and directionality needed for the formation of fibrillar peptide structures. Yet, we could not rule out a contribution of the charged amine and carboxyl moieties at the termini of the short peptide. In order to explore the potential role of electrostatic interaction in the assembly process we have studied a modified non-charged peptide analogue, Ac-Phe–Phe-NH2, in which the N-terminal amine was acetylated and the C-terminal carboxyl was amidated. Scanning and transmission electron microscopy analyses demonstrated that this peptide analogue self-assembles into highly-ordered tubular structures, as observed with the NH2-Phe–Phe-COOH. Also, infrared spectroscopy revealed an amide I absorbance pattern that is very similar to that of the non-modified peptide. Furthermore, an amidated NH2-Phe–Phe-NH2 peptide, which has a net positive charge, also self-assembled into ordered tubular structures. On the other hand, the amine-modified analogues Boc-Phe–Phe-COOH, Z-Phe–Phe-COOH, and Fmoc-Phe–Phe-COOH peptides formed amyloid-like structures that had a significantly smaller diameter. Taken together, the current study further supports our hypothesis regarding the role of aromatic interactions in the self-assembly of amyloid fibrils and amyloid-associated nanostructures that can be modulated by simple chemical modifications.

Amyloidogenic hexapeptide fragment of medin: homology to functional islet amyloid polypeptide fragments

Medin is the main constituent of aortic medial amyloid that occurs in virtually all individuals older than sixty. It is derived from a proteolytic fragment of lactadherin, a mammary epithelial cell expressed glycoprotein that is secreted as part of the milk fat globule membrane. It was previously demonstrated that an octapeptide fragment of medin (NH2-NFGSVQFV-COOH) forms typical well-ordered amyloid fibrils. To obtain further insights into the molecular determinants that mediate this process by such a short peptide fragment, we examined the amyloidogenic potential of its truncated forms and analogues. Our results clearly indicated that a truncated fragment of medin, the hexapeptide, NFGSVQ can form typical amyloid fibrils. A shorter pentapeptide fragment, NFGSV, self-assembled into a gel structure that exhibited a network of fibrous structures. The amyloid forming NFGSVQ hexapeptide is noticeably similar to the short amyloidogenic peptide fragments of the islet amyloid polypeptide (IAPP), NFGAIL and NFLVH. Moreover, the substitution of the phenylalanine residue with either alanine or isoleucine significantly reduced the amyloidogenic potential of the peptide fragment. Taken together, the results are consistent with the assumed role of stacking interactions in the self-assembly processes that lead to the formation of amyloid fibrils. The results are discussed in the context of models for the mechanism of fibril formation and ways to design inhibitors.

Integrating peptide nanotubes in micro-fabrication processes

Self-assembled peptide nanotubes are unique, newly developed nano-structures which exhibit many exciting properties that may establish them as preferred nano-technological building blocks, especially for nano-fluidics, biological sensing and self-assembly applications. Integrating peptide nanotube materials in standard micro-fabrication processes is inhibited by some of their specific characteristics, which make them susceptible to some of the chemicals used in standard lithography. Here, we present an adjusted photo-lithography compatible scheme that allows the integration of these novel new nano-materials in batch processing techniques. Specifically, a scheme for creating nano-fluidic channels using peptide nanotubes, as well as contacting nanotubes to electrodes, is demonstrated. In addition, some of the incompatible fabrication methods are delineated. The modified micro-fabrication processes described here can be extended to other types of sensitive nano-materials.

Bio-inspired antifouling approaches: the quest towards non-toxic and non-biocidal materials

Biofouling is an undesirable process in which organisms and their by-products encrust a surface. Antifouling solutions are of great importance since biofouling has negative effects on numerous species, ecosystems, and areas including water treatment facilities, health-care systems, and marine devices. Many useful solutions have been developed in the last few decades. However, with the emergence of environmental issues, the search for new promising non-toxic materials has expanded. One approach tries to mimic natural antifouling surfaces and relies on mechanisms of action derived from nature. Since these materials are based on natural systems, they are mostly biocompatible and more efficient against complex fouling. In this review, we cover the latest advances in the field of antifouling materials. We specifically focus on biomaterials that are based on the chemical and physical behavior of biological systems.

Probing the interaction of individual amino acids with inorganic surfaces using atomic force spectroscopy.

This article describes single-molecule force spectroscopy measurements of the interaction between individual amino acid residues and inorganic surfaces in an aqueous solution. In each measurement, there is an amino acid residue, lysine, glutamate, phenylalanine, leucine, or glutamine, and each represents a class of amino acids (positively or negatively charged, aromatic, nonpolar, and polar). Force-distance curves measured the interaction of the individual amino acid bound to a silicon atomic force microscope (AFM) tip with a silcon substrate, cut from a single-crystal wafer, or mica. Using this method, we were able to measure low adhesion forces (below 300 pN) and could clearly determine the strength of interactions between the individual amino acid residues and the inorganic substrate. In addition, we observed how changes in the pH and ionic strength of the solution affected the adsorption of the residues to the substrates. Our results pinpoint the important role of hydrophobic interactions among the amino acids and the substrate, where hydrophobic phenylalanine exhibited the strongest adhesion to a silicon substrate. Additionally, electrostatic interactions also contributed to the adsorption of amino acid residues to inorganic substrates. A change in the pH or ionic strength values of the buffer altered the strength of interactions among the amino acids and the substrate. We concluded that the interplay between the hydrophobic forces and electrostatic interactions will determine the strength of adsorption among the amino acids and the surface. Overall, these results contribute to our understanding of the interaction at the organic-inorganic interface. These results may have implications for our perception of the specificity of peptide binding to inorganic surfaces. Consequently, it would possibly lead to a better design of composite materials and devices.