Control of nanoparticle film structure for colloidal lithography

Large area protein patterning reveals nanoscale control of focal adhesion development

Focal adhesion development in cells adherent to surface bound fibronectin presented as 200, 500, or 1000 nm diameter circular patches or as homogeneous controls is studied by fluorescence and scanning electron microscopy. Fundamental cellular processes such as adhesion, spreading, focal adhesion and stress fiber formation are shown to be dependent on the spatial distribution of ligands at this scale. Large area samples enable the study of whole cell populations and opens for new potential applications.

Nanoimprinting using self-assembled ceramic nanoislands

We have combined self-assembled ceramic nanoislands with nanoimprinting to demonstrate a novel, simple, low-cost method for polymer surface patterning. The nanoislands are easy to make and inexpensive, and can produce different distinct island morphologies. With a similar stiffness to steel, the nanoislands have superior durability to silicon, glass, polydimethylsiloxane (PDMS), and other common nanoimprinting materials. The nanoislands are stable up to 1000 degrees C and resist acids, bases, and solvents. We have demonstrated nanoimprinting with PDMS, ethyleneglycol dimethacrylate, and polystyrene polymers. The combination of desirable properties, ease of making, and low cost suggests a useful nanopatterning platform for a wide array of research fields.

On the adsorption behavior of biotin-binding proteins on gold and silica

Streptavidin (SAv), avidin (Av), and neutravidin (NAv) have become widely used molecular tools in biotechnology thanks to their remarkable affinity for biotin. Their tetravalency renders these molecules particularly interesting for the functionalization of solid-liquid interfaces. Using the quartz crystal microbalance with dissipation monitoring, we systematically investigate the deposition of biotin-binding proteins to two surfaces that are popular in biotechnology: gold and silica. We find that simple physisorption of biotin-binding proteins is a viable method to confer biotin-binding functionality to gold surfaces. Both SAv and Av form dense, stable protein monolayers that retain biotin-binding activity and are largely inert to the unspecific binding of bovine serum albumin. Furthermore, we report that SAv resists adsorption to silica over a wide range of pH and ionic strength. The contrast in the binding behavior of SAv on silica and on gold suggests a simple strategy for the selective biofunctionalization of nano- or microstructured surfaces.

Parallel preparation of densely packed arrays of 150-nm gold-nanocrescent resonators in three dimensions

Metallic nanostructures show interesting optical properties due to their plasmonic resonances, and when arranged in three-dimensional (3D) arrays hold promise for optical metamaterials with negative refractive index. Towards this goal a simple, cheap, and parallel method to fabricate large-area, ordered arrays of 150-nm gold nanocrescents supporting plasmonic resonances in the near-infrared spectral range is demonstrated. In this process hexagonally ordered monolayers of monodisperse colloids are prepared by a simple floating technique, and subsequently the individual particles are size-reduced in a plasma process and used as a shadow mask with the initial lattice spacing. The resulting two-dimensional array of plasmonic resonators is coated with a transparent silica layer, which serves as a support for a second layer prepared by the identical process. The mutual orientation of the nanostructures between the individual layers can be freely adjusted, which determines the polarization-dependent absorption of the array and opens the possibility to introduce chirality in this type of 3D metamaterial. The iteration of this simple and efficient methodology yields 3D arrays with optical features as sharp as those of the individual nanocrescents, and shows strong potential for large-scale production of high-quality optical metamaterials.

Nanoprinting onto cells

Growing cells on surfaces bearing nanotopography signals makes many changes in cell gene expression and downstream changes in phenotype but the mechanisms for this have, so far, been obscure. We consider the question of whether the topography directly nanoimprints onto the cell as a component of the signal transduction system. Evidence we present from SEM, TEM and fluorescence detection of the arrangements of cytoskeletal components is consistent with the possibility that cells are nanoimprinted by the substrate. The nanoprinting does not interfere with integrin-mediated adhesion processes and may perhaps work through them. Time-lapse video studies of cells moving from areas bearing nanotopography to flat areas and vice versa suggests that the nanoimprinting takes 1-6h to appear on the cell and a similar time to disappear when the cell moves from a flat surface to a nanotopographic one and back. This nanoprinting of cells would appear to be a novel type of cell signalling.

Particle deposition onto charge-heterogeneous substrates

The deposition of model colloidal particles onto striped charge-heterogeneous surfaces was studied to determine the influence of surface chemical heterogeneity on the deposit morphology. The charge heterogeneity was created employing self-assembled monolayers of carboxyl- and amine-terminated alkanethiols using a soft lithographic technique. Polystyrene sulfate microspheres and fluorescent polystyrene nanoparticles were sequentially deposited onto the patterned substrate under no flow (quiescent) condition. The deposited structures and the micropatterns were imaged using a combination of phase contrast and fluorescence microscopy. The experimental particle deposition behavior was compared to predictions based on random sequential adsorption (RSA) employing a Monte Carlo technique. Comparison of radial distribution obtained from experimental data was made with the theoretical results and found to be in good agreement despite the use of a simple binary probabilistic model in the simulations. The primary conclusion from the study is that particles tend to preferentially deposit at the edges of the favorable stripes. However, the extent of this bias can be controlled by the proximity of consecutive favorable stripes (or width of the intervening unfavorable stripes) as well as the particle size relative to the stripe width. Second, a simple binary probability distribution-based Monte Carlo RSA deposition model adequately predicts the deposit structure, particularly the periodicity of the underlying patterns on the substrate. These observations suggest that the patterns could be encrypted by the deposited particles, which can subsequently be decoded, given the proper "key" or information that is based on analyzing the deposit morphology.

The influence of glancing angle deposited nano-rough platinum surfaces on the adsorption of fibrinogen and the proliferation of primary human fibroblasts

We have used the glancing angle deposition (GLAD) method as a simple and fast method to generate nano-rough surfaces for protein adsorption experiments and cell assays. The surface roughness and the detailed geometrical surface morphology of the thin films were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). As the GLAD deposition angle approaches grazing incidence, sharp and whisker-like columnar protrusions are formed. Smaller and less sharp surface features appear for the thin films synthesized at higher deposition angles. By changing the GLAD deposition angle together with the total amount of mass deposited per area on the respective surfaces, the size of the surface features can be varied on the nanoscale. Using the GLAD topographies as model surfaces, we have investigated the influence of the nano-roughness on fibrinogen adsorption and on the proliferation of primary human fibroblasts. It is found that fibrinogen, an important blood protein, preferentially adheres on the whisker-like nano-rough substrates in comparison to a flat surface. Furthermore, the proliferation of the human fibroblasts is significantly reduced on the nano-rough substrates. These results demonstrate that the GLAD technique can be used to fabricate nano-rough surface morphologies that significantly influence both protein and cellular adhesion to surfaces and are therefore well suited for biological assays.

Preparation and characterization of patchy particles

Anisotropic building blocks are necessary for the self-assembly of complex structures. Methods are reported here for the preparation and characterization of patchy particles. Spherical polymer particles were temporarily bound to a substrate, so that part of their surface is occluded during subsequent surface modification by adsorption of polyelectrolyte. The resulting surface-charge pattern was detected, and its size measured, by means of selective nanoparticle adsorption to this surface. Feasible (roll-to-roll) production rates and process yields are also discussed. In the limit explored here of a single small patch, self-aggregation of patchy particles was observed only at high salt concentration, conditions that suppress anisotropic interactions. Complementary particles however exhibited site-specific binding, to form various anisotropic aggregates.

Self-arrangement among charge-stabilized gold nanoparticles on a dithiothreitol reactivated octanedithiol monolayer

Gold surfaces and structures modified with octanedithiol were reacted with dithiothreitol prior to immersion in buffered solutions of charge stabilized gold nanoparticles. The procedure gives a dithiol layer with adequate properties for a homogeneous octanedithiol monolayer and uniform and reproducible gold nanoparticle binding. The distance between the adsorbing particles is controlled by the particle electrostatic interactions and can be carefully tuned by variation of ionic strength. To some extent, long-range ordering occurs among the adsorbed particles. This behavior is facilitated by the particles' small size compared to the Debye screening but also by the homogeneity of the surface modification. The simple character of the system makes it attractive for fabrication of controlled nanoparticle arrays where further chemical and biological modifications are required.

Synchronized quartz crystal microbalance and nanoplasmonic sensing of biomolecular recognition reactions

We present a method providing synchronized measurements using the two techniques: quartz crystal microbalance with dissipation (QCM-D) monitoring and localized surface plasmon resonance (LSPR). This was achieved by letting a thin gold film perforated with short-ranged ordered plasmon-active nanoholes act as one of the electrodes of a QCM-D crystal. This enabled transmission-mode optical spectroscopy to be used to temporally resolve colorimetric changes of the LSPR active substrate induced upon biomolecular binding events. The LSPR response could thus be compared with simultaneously obtained changes in resonance frequency, Deltaf, and energy dissipation, DeltaD, of the QCM-D device. Since the LSPR technique is preferentially sensitive to changes within the voids of the nanoholes, while the QCM-D technique is preferentially sensitive to reactions on the planar region between the holes, a surface chemistry providing the same binding kinetics on both gold and silica was used. This was achieved by coating the substrate with poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), which was shown to bind in the same manner on silica and gold modified with a carboxyl-terminated thiol. In this way, the combined setup provided new information about structural changes upon PLL-g-PEG adsorption. We also demonstrate subsequent binding of NeutrAvidin and an immunoreaction utilizing biotin-modified IgG. The combined information from the synchronized measurements was also used in a new way to estimate the sensing volume of the LSPR sensor.

Simultaneous nanoplasmonic and quartz crystal microbalance sensing: analysis of biomolecular conformational changes and quantification of the bound molecular mass

This paper presents a study of supported lipid bilayer (SLB) formation and subsequent protein binding using a sensor that combines localized surface plasmon resonance (LSPR) and quartz crystal microbalance with dissipation (QCM-D) monitoring. The LSPR activity arises from silicon oxide (SiO x ) coated nanometric apertures in a thin gold film, which also serves as the active electrode of a QCM-D crystal. Both transducer principles provide signatures for the formation of a SLB upon adsorption and subsequent rupture of adsorbed lipid vesicles. However, the two techniques are sensitive over different regions of the sample: LSPR primarily inside and on the rim of the holes and QCM-D primarily on the planar areas between the holes. Although the dimension of the lipid vesicles is on the same order as the dimension of the nanoholes, it is concluded from the response of the combined system that vesicle rupture in the nanoholes and on the planar region between the holes is synchronized. Furthermore, by determining the thickness of the SLB from the QCM-D response, the characteristic decay length of the LSPR field intensity could be determined. This made it possible not only to determine the mass and refractive index of the homogeneous SLB but also to postulate a generic means to quantify the LSPR response in terms of mass-uptake also for nonhomogeneous films. This is exemplified by measuring the adsorbed lipid mass during vesicle adsorption, yielding the critical lipid vesicle coverage at which spontaneous rupture into a planar bilayer occurs. The generic applicability and versatility of the method is demonstrated from specific protein binding to a functionalized SLB. From the absolute refractive index of the protein, provided from the LSPR data alone, it was possible to determine both the effective thickness of the protein film and the molecular mass (or number) of bound protein.

Two methods to prepare nanorings/nanoholes for the fabrication of vertical nanotransistors

A self-assembled monolayer of polystyrene (PS) beads is formed on a silicon wafer by spin-coating. After drying at 80 °C, a thin film of metal/oxide is deposited. During the deposition, the PS beads are detached due to forces such as the inner stress induced by plasma sputtering deposition, mechanical vibration, and centrifugal shearing induced by substrate rotation, resulting in nanoring/nanohole formation. Further experiments demonstrate that the PS detachment can be controlled by scanning probe microscopy (SPM) tip manipulation. We believe this is a promising set of processes for fabricating nanodevice structures such as those of vertical nanotransistors, which provides high flexibility for nanocrystal characterizations and application for single-electron devices.

Ordered arrays of lead zirconium titanate nanorings

Periodic arrays of nanorings of morphotropic phase boundary lead zirconium titanate (PZT) have been successfully fabricated using a novel self-assembly technique: close-packed monolayers of latex nanospheres were deposited onto Pt-coated silicon substrates, and then plasma cleaned to form ordered arrays of isolated nanospheres, not in contact with each other. Subsequent pulsed laser deposition of PZT, high angle argon ion etching and thermal annealing created the arrays of isolated nanorings, with diameters of ∼100 nm and wall thicknesses of ∼10 nm. Energy dispersive x-ray analysis confirms that the rings are compositionally morphotropic phase boundary PZT, and high resolution transmission electron microscopy imaging of lattice fringes demonstrates some periodicities consistent with perovskite rather than pyrochlore material. The dimensions of these nanorings, and the expected 'soft' behaviour of the ferroelectric material from which they are made, means that they offer the most likely opportunity to date for observing whether or not vortex arrangements of electrical dipoles, analogous to those seen in ferromagnetic nanostructures, actually exist.

Influence of nanotopography on phospholipid bilayer formation on silicon dioxide

We have investigated the effect of well-defined nanoscale topography on the 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid vesicle adsorption and supported phospholipid bilayer (SPB) formation on SiO2 surfaces using a quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). Unilamellar lipid vesicles with two different sizes, 30 and 100 nm, were adsorbed on pitted surfaces with two different pit diameters, 110 and 190 nm, as produced by colloidal lithography, and the behavior was compared to results obtained on flat surfaces. In all cases, complete bilayer formation was observed after a critical coverage of adsorbed vesicles had been reached. However, the kinetics of the vesicle-to-bilayer transformation, including the critical coverage, was significantly altered by surface topography for both vesicle sizes. Surface topography hampered the overall bilayer formation kinetics for the smaller vesicles, but promoted SPB formation for the larger vesicles. Depending on vesicle size, we propose two modifications of the precursor-mediated vesicle-to-bilayer transformation mechanism used to describe supported lipid bilayer formation on the corresponding flat surface. Our results may have important implications for various lipid-membrane-based applications using rough or topographically structured surfaces.

Transport effects in the oxygen reduction reaction on nanostructured, planar glassy carbon supported Pt/GC model electrodes

The role of transport and re-adsorption processes on the oxygen reduction reaction (ORR), and in particular on its selectivity was studied using nanostructured model electrodes consisting of arrays of Pt nanostructures of well-defined size and separation on a planar glassy carbon (GC) substrate. The electrochemical measurements were performed under controlled transport conditions in a double-disk electrode thin-layer flow-cell configuration; the model electrodes were fabricated by colloidal lithography techniques, yielding Pt nanostructures of well defined and controlled size and density (diameter: 140 or 85 nm, height: 20 or 10 nm, separation: from 1-2 to more than 10 diameters). The nanostructured model electrodes were characterized by scanning electron microscopy and electrochemical probing of the active surface area (via the hydrogen adsorption charge). The electrocatalytic measurements revealed a pronounced variation of the hydrogen peroxide yield, which increases by up to two orders of magnitude with increasing separation and decreasing size of the Pt nanostructures. Similar, though less pronounced effects were observed upon varying the electrolyte flow and thus the mass transport characteristics. These effects are discussed in a reaction model which includes (i) direct reduction to H(2)O on the Pt surface and (ii) additional H(2)O(2) formation and desorption on both Pt and carbon surfaces and subsequent partial re-adsorption and further reduction of the H(2)O(2) molecules on the Pt surface.

From particle self-assembly to functionalized sub-micron protein patterns

Biologically relevant nanopatterns are useful platforms to address fundamental questions, for example, regarding protein-protein and cell-protein interactions. For the creation of nanopatterns, complex and expensive instrumentation is often needed. We present a simple but versatile patterning method using a combination of particle and subsequent molecular self-assembly to produce ordered structures in the micron and sub-micron range. Polystyrene particles were, in a first step, assembled via dip-coating or dried in a drying cell. Silicon wafers and glass slides coated with SiO(2) and a top layer of 11 nm of TiO(2) were used as substrates. Large hexagonally ordered particle monolayers were formed with high reproducibility. These were subsequently shrunk in a controlled manner by exposure to a O(2)/N(2) plasma and subsequently used as etching masks to transfer the particle pattern onto the substrate, creating TiO(2) features in an SiO(2) background. After removing the mask the oxide contrast was translated in three simple dip-and-rinse steps into a biochemical contrast of protein-coated features in an inert background. In short, alkane phosphates were first selectively adsorbed to the TiO(2) features. Then the SiO(2) background was backfilled using poly(L-lysine)-graft-poly(ethylene glycol) and finally streptavidin was adsorbed to the hydrophobic alkane phosphate SAMs, allowing subsequent binding and hybridization of biotinylated DNA.

Supported lipid bilayer formation and lipid-membrane-mediated biorecognition reactions studied with a new nanoplasmonic sensor template

This paper presents the use of the localized surface plasmon resonance (LSPR) sensor concept to probe the formation of macroscopic and laterally mobile supported lipid bilayers (SLBs) on SiOx-encapsulated nanohole-containing Au and Ag films. A comparison between Au- and Ag-based sensor templates demonstrates a higher sensitivity for Au-based templates with respect to both bulk and interfacial refractive index (RI) changes in aqueous solution. The lateral mobility of SLBs formed on the SiOx-encapsulated nanohole templates was analyzed using fluorescence recovery after photobleaching (FRAP), demonstrating essentially complete (>96%) recovery, but a reduction in diffusivity of about 35% compared with SLBs formed on flat SiOx substrates. Furthermore, upon SLB formation, the temporal variation in extinction peak position of the LSPR active templates display a characteristic shape, illustrating what, to the best of our knowledge, is the first example where the nanoplasmonic concept is shown capable of probing biomacromolecular structural changes without the introduction of labels. With a signal-to-noise ratio better than 5 x 10(2) upon protein binding to the cell-membrane mimics, the sensor concept is also proven competitive with state-of-the-art label-free sensors.

Viscoelastic modeling of highly hydrated laminin layers at homogeneous and nanostructured surfaces: quantification of protein layer properties using QCM-D and SPR

The adsorption of proteins at material surfaces is important in applications such as biomaterials, drug delivery, and diagnostics. The interaction of cells with artificial surfaces is mediated through adsorbed proteins, where the type of protein, amount, orientation, and conformation are of consequence for the cell response. Laminin, an important cell adhesive protein that is central in developmental biology, is studied by a combination of quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance (SPR) to characterize the adsorption of laminin on surfaces of different surface chemistries. The combination of these two techniques allows for the determination of the thickness and effective density of the protein layer as well as the adsorbed mass and viscoelastic properties. We also evaluate the capacity of QCM-D to be used as a quantitative technique on a nanostructured surface, where protein is adsorbed specifically in a nanopattern exploiting PLL-g-PEG as a protein-resistant background. We show that laminin forms a highly hydrated protein layer with different characteristics depending on the underlying substrate. Using a combination of QCM-D and atomic force microscopy (AFM) data from nanostructured surfaces, we model laminin and antibody binding to nanometer-scale patches. A higher amount of laminin was found to adsorb in a thicker layer of a lower effective density in nanopatches compared to equivalent homogeneous surfaces. These results suggest that modeling of QCM-D data of soft viscoelastic layers arranged in nanopatterns may be applied where an independent measure of the "dry" mass is known.

Simulation study of random sequential adsorption of mixtures on a triangular lattice

Random sequential adsorption of binary mixtures of extended objects on a two-dimensional triangular lattice is studied numerically by means of Monte Carlo simulations. The depositing objects are formed by self-avoiding random walks on the lattice. We concentrate here on the influence of the symmetry properties of the shapes on the kinetics of the deposition processes in two-component mixtures. Approach to the jamming limit in the case of mixtures is found to be exponential, of the form: theta(t) approximately theta jam - Deltatheta exp(- t/sigma), and the values of the parameter sigma are determined by the order of symmetry of the less symmetric object in the mixture. Depending on the local geometry of the objects making the mixture, jamming coverage of a mixture can be either greater than both single-component jamming coverages or it can be in between these values. Results of the simulations for various fractional concentrations of the objects in the mixture are also presented.

Human fibroblast and human bone marrow cell response to lithographically nanopatterned adhesive domains on protein rejecting substrates

The separate influence of topographical and chemical cues on cell attachment and spreading are well documented; however, that of duel-cue substrates is less so. In this study graft copolymers that sterically stabilize biological surfaces were employed alongside nanotopographical features fabricated by colloidal lithography. This resulted in the production of a range of substrates whereby the effect of chemistry and or topography on both on human fibroblast and bone marrow cell adhesion and spreading could be observed. The current studies indicate an enhancement of cell response as a consequence of modifications in material topography, whereas the current selected chemical cues inhibited cell function. Critically, in combination, topography modulated the effects of chemical environment.

Nanostructured Pt/GC model electrodes prepared by the deposition of metal-salt-loaded micelles

Novel, nanostructured, carbon-supported Pt model electrodes with homogeneously distributed Pt nanoparticles of uniform size were fabricated and analyzed with respect to their electrochemical properties. For this purpose, Pt-salt-loaded micelles were deposited on a glassy carbon substrate and subsequently exposed to an oxygen plasma and a H2 atmosphere for removal of the polymer carriers and reduction of the Pt salt. The morphology of the resulting nanoparticles and their electrochemical/electrocatalytic properties were characterized by high-resolution scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and differential electrochemical mass spectrometry for CO electrooxidation. The data demonstrate that this method is generally suited to the production of nanostructured model electrodes with well-defined and independently adjustable particle size and interparticle distance distributions, which are specifically suited for quantitative studies of transport processes in electrocatalytic reactions.

Colloidal lithography and current fabrication techniques producing in-plane nanotopography for biological applications

Substrate topography plays a vital role in cell and tissue structure and function in situ, where nanometric features, for example, the detail on single collagen fibrils, influence cell behaviour and resultant tissue formation. In vitro investigations demonstrate that nanotopography can be used to control cell reactions to a material surface, indicating its potential application in tissue engineering and implant fabrication. Developments in the catalyst, optical, medical and electronics industries have resulted in the production of nanopatterned surfaces using a variety of methods. The general protocols for nanomanufacturing require high resolution and low cost for fabricating devices. With respect to biological investigations, nanotopographies should occur across a large surface area (ensuring repeatability of experiments and patterning of implant surfaces), be reproducible (allowing for consistency in experiments), and preferably, accessible (limiting the requirement for specialist equipment). Colloidal lithography techniques fit these criteria, where nanoparticles can be utilized in combination with a functionalized substrate to produce in-plane nanotopographies. Subsequent lithographic processing of colloidal substrates utilizing, for example, reactive ion etching allows the production of modified colloidal-derived nanotopographies. In addition to two-dimensional in-plane nanofabrication, functionalized structures can be dip coated in colloidal sols, imparting nanotopographical cues to cells within a three-dimensional environment.

Study of Staphylococcus aureus adhesion on a novel nanostructured surface by chemiluminometry

In recent years the progress in the field of nanotechnologies has offered new possibilities to control the superficial features of implant materials down to a nanoscale level. Several studies have therefore tried to explore the effects of nanostructured biomaterial surfaces on the behavior of eukaryotic cells. However, nanotopography could exert an influence also on the behavior of prokaryotic cells, with relevant implications concerning the susceptibility of implant surfaces to infection. Aim of this study was to examine the behavior of Staphylococcus aureus on polyethylene terephthalate (PET) surfaces either cylindrically nanostructured (PET-N) or flat ion-etched (PET-F), and on tissue culture-grade polystyrene (PS). Microbial adherence was assessed by chemiluminometry under 4 different conditions: (a) bacteria suspended in MEM medium, (b) bacteria in MEM supplemented with 10% fetal bovine serum (FBS), (c) test surfaces preconditioned in FBS, and (d) post-exposure of colonised surfaces to serum-supplemented MEM. Under all circumstances, PET-F and PET-N specimens showed identical bacterial adhesion properties. In the absence of serum, all 3 test materials showed a very high adhesivity to microbial cells and both PET surfaces exhibited greater adhesion than PS. On the contrary, the presence of 10% serum in solution significantly affected cell behavior: the number of microbial cells on all surfaces was drastically reduced, and the adhesion properties of PET surfaces with respect to PS were reversed, with PET being less adhesive. Overall, the specific cylindrical nanostructures created on PET did not significantly influence microbial behavior. Ongoing studies are verifying whether other nanotopographies with different geometry could have more substantial effects.

Nanomechanotransduction and Interphase Nuclear Organization influence on genomic control

The ability of cells to alter their genomic regulation in response to mechanical conditioning or through changes in morphology and the organization of the interphase nuclei are key questions in cell biology. Here, two nanotopographies have been used as a model surfaces to change cell morphology in order to investigate spatial genomic changes within the nuclei of fibroblasts. Initially, centromeres for chromosome pairs were labeled and the average distance on different substrates calculated. Further to this, Affymetrix whole genome GeneChips were used to rank genomic changes in response to topography and plot the whereabouts on the chromosomes these changes were occurring. It was seen that as cell spreading was changed, so were the positions along the chromosomes that gene regulations were being observed. We hypothesize that as changes in cell and thus nuclear morphology occur, that this may alter the probability of transcription through opening or closing areas of the chromosomes to transcription factors.

Nano Patterned Surfaces for Biomaterial Applications

Bionanotechnology has seen much interest in the past few years. The development in new nanotechnologies and the transfer of such to biomedical applications has been received with large expectations. Here we will describe some of the most common techniques to prepare surfaces with nanometric sized features and how they have been applied to control cell behavior. The focus, however, will be on electron beam lithography and its use in biological applications. We will show that such highly ordered surfaces exhibit low adhesive properties for cells. Also, such topographies change the wetting properties to be either more hydrophilic or hydrophobic depending on the surface energy of the flat surface. Today, little research has found its way to the commercial market. This is mainly down to the ability to make large areas or large quantities of nano patterned materials. We will describe a few methods by which we think it would be possible to mass produce nano topographically patterned surfaces.

Hole-enhanced Raman scattering

Stokes and anti-Stokes non-resonant hole-enhanced Raman scattering (HERS) spectra with high signal-to-noise ratio (S/N) are reported for the first time for aqueous phase R6G molecules adsorbed onto random nanoholes in thin gold films. Compared to conventional surface-enhanced Raman scattering from nanometric gold colloid particles, HERS exhibits higher strength gain, exceptional reproducibility, simple and reliable substrate preparation, and excellent mechanical stability. By correlating the hole density with Raman scattering gain, we determined optimum HERS gain for 50 nm diameter holes at approximately 100 holes/microm(2). Providing a Raman substrate with uniform "hot spots", we expect that HERS will make the quantitative Raman analysis of biological molecules possible.

Large area protein nanopatterning for biological applications

Large area nanopatterns of functional proteins are demonstrated. A new approach to analyze atomic force microscopy height histograms is used to quantify protein and antibody binding to nanoscale patches. Arrays of nanopatches, each containing less than 40 laminin molecules, are shown to be highly functional binding close to 1 monoclonal anti-laminin IgG (site by IKVAV sequence) or 3-4 polyclonal anti-laminin IgG's per surface bound laminin. Complementary quartz crystal microbalance measurements indicate higher functionality at nanopatches than on homogeneous surfaces.

Improving the Instrumental Resolution of Sensors Based on Localized Surface Plasmon Resonance

The colorimetric variations induced upon changes in interfacial refractive index of nanoscale noble metal structures exhibiting localized surface plasmon resonance (LSPR) provides a convenient means of label-free, affinity-based detection of biomolecular recognition reactions. However, despite being similar in nature to conventional SPR, LSPR has so far suffered from significantly lower data quality in terms of its signal-to-noise ratio (S/N) in typical biomolecular recognition analysis. In this work, generic data analysis algorithms and a simple experimental setup that provide a S/N upon protein binding that is comparable to that of state-of-the art SPR systems are presented. Specifically, it is demonstrated how temporal variations (rate approximately 0.5 Hz) in parameters proportional to the resonance peak position can be recorded simultaneously, yielding a peak position precision of <5 x 10(-4) nm and an extinction noise level of <5 x 10(-6) absorbance units (Abs). This, in turn, is shown to provide a S/N of approximately 2000 (equivalent to a detection limit of <0.1 ng/cm(2)) for typical protein binding reactions. Furthermore, the importance of utilizing changes in both peak position and magnitude is highlighted by comparing different LSPR active noble metal architectures that respond differently to bulk and interfacial refractive index changes.

Multiscale-linking simulation of irreversible colloidal deposition in the presence of DLVO interactions

An efficient multiscale-linking algorithm, based on the self-consistent integration of Brownian dynamics simulation of particle trajectories with the solution of the continuum-level conservation equation for particle concentration subject to an adaptive Neumann boundary condition that accounts for the blocking effect of deposition, is developed. The algorithm has been already validated in the case of deposition of noninteracting hard spheres [R.V. Magan, R. Sureshkumar, Multiscale Model. Simul. 2 (2004) 475]. In this study, the above algorithm is extended to incorporate particle interactions modeled by the DLVO theory. The simulations are used to identify a time scale at which the deposition process transitions from a power-law to an asymptotic regime. Detailed characterization of the two regimes is provided for a wide range of ionic strength, particle surface charge density, bulk volume fraction, and substrate potential values. The radial distribution functions obtained for various ionic strengths can be collapsed into a master curve when the radial distance is normalized with respect to a characteristic length scale of inter-particle repulsion. Moreover, simulation results suggest a rescaled, uniformly valid soft random sequential adsorption (RSA) model. Simulation results for the kinetics and monolayers structure compare favorably with experimental data, without the use of adjustable parameters. Comparison with other dynamic simulation techniques shows that while their predictions are qualitatively similar, notable quantitative differences exist especially for small ionic strengths.

Methods for Fabrication of Nanoscale Topography for Tissue Engineering Scaffolds

Observations of how controlling the microenvironment of cell cultures can lead to changes in a variety of parameters has lead investigators to begin studying how the nano-environment of a culture can affects cells. Cells have many structures at the nanoscale such as filipodia and cytoskeletal and membrane proteins that interact with the environment surrounding them. By using techniques that can control the nano-environment presented to a cell, investigators are beginning to be able to mimic the nanoscale topographical features presented to cells by extracellular matrix proteins such as collagen, which has precise and repeating nano-topography. The belief is that these nanoscale surface features are important to creating more natural cell growth and function. A number of techniques are currently being used to create nanoscale topographies for cell scaffolding. These techniques fall into two main categories: techniques that create ordered topographies and those that create unordered topographies. Electron Beam lithography and photo-lithography are two standard techniques for creating ordered features. Polymer demixing, phase separation, colloidal lithography and chemical etching are most typically used for creating unordered surface patterns. This review will give an overview of these techniques and cite observations from experiments carried out using them.

Nanofabrication of Polymer Surfaces Utilizing Colloidal Lithography and Ion Etching

In this paper, we utilize colloidal lithography based on electrostatic self-assembly of polystyrene colloidal particles onto a polymer surface as a nanoscale mask. The pattern is then transferred to the surface by ion beam etching. Each particle acts as an individual mask, resulting in an array of identical structure. Ion beam exposure etches away the unmasked surface between the particles, so the particle mask pattern can be transferred into the polymer surface. This method allows to nanofabricate bulk polymeric surfaces with systematic variation in relief, structure sizes, and aspect ratios. It is a fast, simple, and reliable method to fabricated different polymeric surfaces even on large area samples (> 1 cm2). The structural variation is achieved by use of different conditions during the self-assembly of the mask (e.g., different particles sizes) or different ion etching conditions during the pattern transfer (e.g., ion energy, ion flux, ion incident angle, etching time, gas environment).

Osteoprogenitor response to semi-ordered and random nanotopographies

In bone tissue engineering, it is desirable to use materials to control the differentiation of mesenchymal stem cell populations in order to gain direct bone apposition to implant materials. It has been known for a number of years that microtopography can alter cell adhesion, proliferation and gene expression. More recently, the literature reveals that nanotopography is also of importance. Here, the reaction of primary human osteoprogenitor cell populations to nanotopographies down to 10 nm in size is considered. The topographies were originally produced by colloidal lithography and polymer demixing on silicon and then embossed (through an intermediate nickel shim) into polymethylmethacrylate. The biological testing considered cell morphology (image analysis of cell spreading and scanning electron microscopy), cell cytoskleton and adhesion formation (fluorescent staining of actin, tubulin, vimentin and vinculin) and then subsequent cell growth and differentiation (fluorescent staining of osteocalcin and osteopontin). The results demonstrated that the nanotopographies stimulated the osteoprogenitor cell differentiation towards an osteoblastic phenotype.

Plasmonic sensing characteristics of single nanometric holes

The optical response of isolated holes in 20 nm thin gold is probed as a function of alkanethiol CH(3)(CH2)x SH (x epsilon in 1-15) and protein adsorption using dark-field spectroscopy. We establish that the plasmon excitations of single and short-range ordered 60 nm holes exhibit similar E-field decay lengths delta approximately 10-20 nm and that a single hole can be used to resolve the successive adsorption of a protein (biotin-BSA) and its interaction partner (neutravidin). The data confirm the localized character of the hole plasmon and demonstrate that its applicability for bio/chemosensing is similar to that of particle plasmons.

Nanowell-array surfaces prepared by argon plasma etching through a nanopore alumina mask

A method for preparing a glass surface containing an ordered array of nanowells is described. These nanowell arrays are prepared via a plasma-etch method using a nanopore alumina film as the etch mask. A replica of the pore structure of the alumina mask is etched into the glass. We demonstrate that chemical information in the form of negatively charged latex nanoparticles can be selectively stored within these nanowells and not indiscriminately deposited on the surface surrounding the nanowells. To accomplish this, the chemistry of the glass surfaces within these nanowells (walls and bottoms) must be different from the chemistry of the surface surrounding the nanowells. Two different procedures were developed to make the inside vs. surrounding surface chemistries different. Atomic force microscopy (AFM) was used to image the nanowells and, via friction-force measurements, to prove that the inner nanowell surfaces can be made chemically different from the surface surrounding the nanowells.