Tubular nanostructures are suggested to have a wide range of applications in nanotechnology. We report our observation of the self-assembly of a very short peptide, the Alzheimer's beta-amyloid diphenylalanine structural motif, into discrete and stiff nanotubes. Reduction of ionic silver within the nanotubes, followed by enzymatic degradation of the peptide backbone, resulted in the production of discrete nanowires with a long persistence length. The same dipeptide building block, made of D-phenylalanine, resulted in the production of enzymatically stable nanotubes.
A simple dipeptide self‐assembles into a biocompatible hydrogel (see figure and inside cover). This novel biomaterial is extremely simple to prepare and has a remarkable rigidity. It is very stable under extreme conditions, can be injected, and can be shaped according to the vessel it has been assembled in. The hydrogel allows a wide variety of possible biomedical applications including tissue engineering, axonal regeneration, and controlled drug release.
Controlling the spatial organization of objects at the nanoscale is a key challenge in enabling their technological application. Biomolecular assemblies are attractive nanostructures owing to their biocompatibility, straightforward chemical modifiability, inherent molecular recognition properties and their availability for bottom-up fabrication. Aromatic peptide nanotubes are self-assembled nanostructures with unique physical and chemical stability and remarkable mechanical rigidity. Their application in the fabrication of metallic nanowires and in the improvement of the sensitivity of electrochemical biosensors have already been demonstrated. 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.
This paper describes the use of a modified x,y-plotter to generate hydrophilic channels by printing a solution of hydrophobic polymer (poly(dimethyl siloxane; 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 (3D) 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 (6.5) from samples with slightly acidic pH (8.0). The work also describes using printed devices that can be loaded using multipipettes, and printed flexible, foldable channels in paper over areas larger than 100 cm 2 . This paper describes the use of a modified desktop plotter to fabricate simple patterns of hydrophilic microchannels in paper. We defined the boundaries of the microchannels by printing a solution of poly(dimethyl siloxane) (PDMS) in hexanes onto filter paper, using an x,y-plotter as a print-engine. Because PDMS is an elastomer, the paper could be bent and folded, without destroying the integrity of the channels. The channels have a minimum width of 1 mm, and the minimum spacing between two channels can be as small as 1 mm. These dimensions are large relative to those normally encountered in microfluidic systems, but they are the right size for the basic analytical and diagnostic devices that are our primary objectives, since readout of these devices will often involve visual observations of unmagnified spots of analytes. 1 We believe that this low-cost system for printing hydrophobic polymers and other materials on paper will be useful for prototyping simple paper-based diagnostics assays.A variety of simple diagnostic tests (for example, "dip-stick" tests) rely on paper-based assays. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] Some of these tests analyze environmental conditions, 16,17 or detect illness (often in the developing world). [18][19][20] We have recently patterned paper into hydrophilic regions demarcated by hydrophobic walls using photolithography and conventional photoresists (SU-8; and poly(methyl methacrylate), or PMMA). 1 The hydrophilic regions act as microfluidic channels, in which capillary action wicks aqueous samples into the device. This design provides the basis for diagnostic systems in paper that are more complex than the simplest dip-stick assays (in the sense that multiple assays can be performed on a small array with ~5-20 μL of blood, urine, or other fluid), but simpler and more affordable than highertechnology microfluidic assays. 20 An advantage of using PDMS to pattern the p...
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