Donald T. Haynie

DNA nanowire fabrication

Deoxyribonucleic acid (DNA) has been a key building block in nanotechnology since the earliest work on what is now called DNA-templated self-assembly (Alivisatos et al 1996 Nature 382 609; Mirkin et al 1996 Nature 382 607; Braun et al 1998 Nature 391 775). A range of different nanoparticles and nanoclusters have been assembled on single DNA molecules for a variety of purposes (Braun et al 1998 Nature 391 775; Richter et al 2001 Appl. Phys. Lett. 78 536; Park et al 2002 Science 295 1503; Mirkin 2000 Inorg. Chem. 39 2258; Keren et al 2003 Science 302 1380). Electrically conductive silver (Braun et al 1998 Nature 391 775) and palladium (Richter et al 2001 Appl. Phys. Lett. 78 536) nanowires, for example, have been fabricated by DNA templating for the development of interconnection of nanoelectric elements, and field effect transistors have been built by assembly of a single carbon nanotube and DNA-templated nanowires (Keren et al 2003 Science 302 1380). DNA is well suited for nanowire assembly because of its size, well organized structure, and exquisite molecular-recognition-ability-specific base pairing. This property has been used to detect nucleic acids (Park et al 2002 Science 295 1503) and anthrax (Mirkin 2000 Inorg. Chem. 39 2258) with high sensitivity and specificity. Molecular recognition can also be used to localize nanowires in electronics. Various methods, for example molecular combing, electrophoretic stretching, and hydrodynamic stretching, have been developed to orient DNA molecules on a solid support. This review focuses on methods used to manipulate and metallize DNA in nanowire fabrication. A novel approach based on a single-stranded DNA template and molecular recognition is also discussed.

Protein- and peptide-based electrospun nanofibers in medical biomaterials

UNLABELLED Electrospun fibers are being studied and developed because they hold considerable promise for realizing some advantages of nanostructured materials. The fibers can be made of biocompatible and biodegradable polymers. Electrospinning has therefore attracted interest in biotechnology and medicine, and there has been rapid growth in this area in recent years. This review presents an introduction to polymer nanofiber electrospinning, focusing on the use of natural proteins and synthetic peptides. We summarize key physical properties of protein-based and peptide-based nanofiber mats, survey biomedical applications of these materials, identify key challenges, and outline future prospects for development of the technology for tissue engineering, drug delivery, wound healing, and biosensors. FROM THE CLINICAL EDITOR This review focuses on polymer nanofiber electrospinning using natural proteins and synthetic peptides. The authors describe key properties and applications of these materials, and outline future prospects for tissue engineering, drug delivery, wound healing, and biosensors based on these nanomats and nanofibers.

Cobalt metallization of DNA: toward magnetic nanowires

Co nanoparticles have been assembled in situ on a template of double-stranded deoxyribonucleic acid (DNA) to form magnetic nanowires. DNA was immobilized on freshly cleaved mica or silanized glass and oriented by molecular combing. Pd(II) ions bound to DNA were reduced to zero-valence nanoclusters, which selectively catalysed deposition of Co(0) in a dimethylamine borane (DMAB)-based reducing bath. Co nanoclusters grew only where Pd nuclei were localized on the DNA template. Material characterization by UV–vis spectroscopy (UVS), atomic force microscopy (AFM), and energy dispersive x-ray (EDX) spectroscopy revealed that the fabrication process resulted in the formation of Co nanowires microns long and 10–20 nm thick.

Antimicrobial polypeptide multilayer nanocoatings

A multilayer coating (or film) of nanometer-thick layers can be made by sequential adsorption of oppositely charged polyelectrolytes on a solid support. The method is known as layer-by-layer assembly (LBL). No special apparatus is required for LBL and nanofilms can be prepared under mild, physiological conditions. A multilayer nanofilm in which at least one of the constituent species is a polypeptide is a polypeptide multilayer nanofilm. The present work was aimed at assessing whether polypeptide multilayer nanofilms with specific antimicrobial properties could be prepared by incorporation of a known antimicrobial agent in the film structure, in this case the edible protein hen egg white lysozyme (HEWL). The chicken enzyme is widely employed as a human food preservative. An advantage of LBL in this context is that the nanofilm is fabricated directly on the surface of interest, eliminating the need to incorporate the antimicrobial in other packaging materials. Here, nanofilms were made of poly(L-glutamic acid) (PLGA), which is highly negatively charged in the mildly acidic pH range, and HEWL, which has a high net positive charge at acidic pH. We show that PLGA/HEWL nanofilms inhibit growth of the model microbe Microccocus luteus in the surrounding liquid medium. The amount of HEWL released from PLGA/HEWL films depends on the number of HEWL layers and therefore on the total quantity of HEWL in the films. This initial study provides a sketch of the scope for further development of LBL in the area of antimicrobial polypeptide multilayer films. Potential applications of such films include strategies for food preservation and coatings for implant devices.

Measurement of the traction force of biological cells by digital holography

The traction force produced by biological cells has been visualized as distortions in flexible substrata. We have utilized quantitative phase microscopy by digital holography (DH-QPM) to study the wrinkling of a silicone rubber film by motile fibroblasts. Surface deformation and the cellular traction force have been measured from phase profiles in a direct and straightforward manner. DH-QPM is shown to provide highly efficient and versatile means for quantitatively analyzing cellular motility.

Four-dimensional motility tracking of biological cells by digital holographic microscopy

Abstract. Three-dimensional profiling and tracking by digital holography microscopy (DHM) provide label-free and quantitative analysis of the characteristics and dynamic processes of objects, since DHM can record real-time data for microscale objects and produce a single hologram containing all the information about their three-dimensional structures. Here, we have utilized DHM to visualize suspended microspheres and microfibers in three dimensions, and record the four-dimensional trajectories of free-swimming cells in the absence of mechanical focus adjustment. The displacement of microfibers due to interactions with cells in three spatial dimensions has been measured as a function of time at subsecond and micrometer levels in a direct and straightforward manner. It has thus been shown that DHM is a highly efficient and versatile means for quantitative tracking and analysis of cell motility.

FDTD simulation of exposure of biological material to electromagnetic nanopulses

Ultra-wideband (UWB) electromagnetic pulses of nanosecond duration, or nanopulses, are of considerable interest to the communications industry and are being explored for various applications in biotechnology and medicine. The propagation of a nanopulse through biological matter has been computed using the finite difference-time domain (FDTD) method. The approach required the reparametrization of existing Cole-Cole model-based descriptions of dielectric properties of biological matter in terms of the Debye model without loss of accuracy. Several tissue types have been considered. Results show that the electromagnetic field inside biological tissue depends on incident pulse rise time and width. Rise time dominates pulse behaviour inside tissue as conductivity increases. It has also been found that the amount of energy deposited by 20 kV m(-1) nanopulses is insufficient to change the temperature of the exposed material for pulse repetition rates of 1 MHz or less, consistent with recent experimental results.

Fine tuning of physical properties of designed polypeptide multilayer films by control of pH.

Adjustment of pH can alter the ensemble of three‐dimensional structures of a polypeptide in solution by changing the distribution of charge and Coulombic interactions. The role of pH in layer‐by‐layer self‐assembly (LbL) of designed 32mer peptides containing the amino acid cysteine has been investigated using a combination of physical methods. Results show that pH can have a substantial influence on the mass of adsorbed peptide, surface roughness, and film density over a range of 1.5 pH units. Peptide film thickness depends on the number of layers, as with “conventional” polyelectrolytes. Film density and morphology, however, vary more with pH than does thickness, translating into a change in density on the order of 70% over the pH range 7.4–8.9. Results of this work provide insight on the physical basis of LbL and suggest that peptides are a promising class of polyelectrolytes for the creation of designer thin films for applications in biotechnology and other areas.

Design of peptides for thin films, coatings and microcapsules for applications in biotechnology

A highly-interdisciplinary approach has been developed for minimizing the immunogenicity of films, coatings, microcapsules and other nano-structured materials fabricated from designed polypeptide chains. It is to base the amino-acid sequences on solvent-exposed regions in the folded states of proteins from the same organism. Each such region that meets defined criteria with respect to charge is called a sequence motif. The approach becomes more specifically tailored for intravenous applications by requiring an employed sequence motif to correspond to a known blood protein. An algorithm has been developed to identify sequence motifs in protein-encoding regions of a genome. This work is focused on sequence motifs of charge per unit length >0.5 at neutral pH. It has been found that the number of unique sequence motifs meeting this criterion in available human genome data is maximal for motifs of approx. 7 residues in length. We have designed polypeptides on the basis of computational analysis and shown that they can be used to fabricate nano-structured thin films by electrostatic layer-by-layer assembly (ELBL). The results of this work are discussed with a view to possible applications in biotechnology, notably development of biocompatible coatings and microcapsules.

Molecular physiology of the tensin brotherhood of integrin adaptor proteins

Numerous proteins have been identified as constituents of the adhesome, the totality of molecular components in the supramolecular assemblies known as focal adhesions, fibrillar adhesions and other kinds of adhesive contact. The transmembrane receptor proteins called integrins are pivotal adhesome members, providing a physical link between the extracellular matrix (ECM) and the actin cytoskeleton. Tensins are ever more widely investigated intracellular adhesome constituents. Involved in cell attachment and migration, cytoskeleton reorganization, signal transduction and other processes relevant to cancer research, tensins have recently been linked to functional properties of deleted in liver cancer 1 (DLC1) and a mitogen‐activated protein kinases (MAPK), to cell migration in breast cancer, and to metastasis suppression in the kidney. Tensins are close relatives of phosphatase homolog/tensin homolog (PTEN), an extensively studied tumor suppressor. Such findings are recasting the earlier vision of tensin (TNS) as an actin‐filament (F‐actin) capping protein in a different light. This critical review aims to summarize current knowledge on tensins and thus to highlight key points concerning the expression, structure, function, and evolution of the various members of the TNS brotherhood. Insight is sought by comparisons with homologous proteins. Some historical points are added for perspective. Proteins 2014; 82:1113–1127.