Multiscale patterning of nanocomposite polyelectrolyte/nanoparticle films using inkjet printing and AFM scratching

The fabrication of structured polymer/nanoparticle composite films through a combination of additive, subtractive and self-assembly methodologies is investigated. Consumer grade inkjet printing hardware is employed to deposit cationic polyelectrolytes on (i) hydrophilic and (ii) hydrophobised glass substrates. The hydrophobisation process controls the spreading of the droplets and hence the lateral size of printed features. The printed cationic polyelectrolyte regions are used as a template to direct the self-assembly of negatively charged gold nanoparticles onto the surface. Micro-scale features are created in the polyelectrolyte/nanoparticle films using AFM scratching to selectively displace material. The effect of substrate wettability on film morphology is discussed

Accurate micron-scale modification of AFM cantilevers

Atomic force microscopy has provided the modern researcher with the ability to perform accurate force measurements between a probe and a surface. The data obtained can be used in the development of biosensors, surfactants, and materials with enhanced properties, to name only a few applications. The atomic force microscope (AFM) is undoubtedly suited for making repeated force measurements. Standard AFM cantilevers can be modified through the attachment of a colloid probe such as silica, and employed in the analysis of forces between surfaces. Resin-based or glass bond adhesives are suitable for probe bonding, as they are insoluble in water once set. However, such adhesives often require heating to reduce their viscosity, which makes the procedure quite difficult to carry out. The particle is usually attached to the apex of the cantilever, so that measurements can be performed with optimum force resolution. Particle attachment is traditionally carried out under an optical microscope using thin wire as a guide. However, there is no guarantee that the colloid particle has been accurately positioned on the apex of the cantilever

Bio-nanopatterning of Surfaces

Bio-nanopatterning of surfaces is a very active interdisciplinary field of research at the interface between biotechnology and nanotechnology. Precise patterning of biomolecules on surfaces with nanometre resolution has great potential in many medical and biological applications ranging from molecular diagnostics to advanced platforms for fundamental studies of molecular and cell biology. Bio-nanopatterning technology has advanced at a rapid pace in the last few years with a variety of patterning methodologies being developed for immobilising biomolecules such as DNA, peptides, proteins and viruses at the nanoscale on a broad range of substrates. In this review, the status of research and development are described, with particular focus on the recent advances on the use of nanolithographic techniques as tools for biomolecule immobilisation at the nanoscale. Present strengths and weaknesses, as well future challenges on the different nanolithographic bio-nanopatterning approaches are discussed

Room temperature thermally evaporated thin Au film on Si suitable for application of thiol self-assembled monolayers in MEMS/NEMS sensors

Gold is a standard surface for attachment of thiol-based self-assembled monolayers (SAMs). To achieve uniform defect free SAM coatings, which are essential for bio/chemical sensing applications, the gold surface must have low roughness, and be highly orientated. These requirements are normally achieved by either heating during Au deposition or post deposition Au surface annealing. This paper shows that room temperature deposited gold, can afford equivalent gold surfaces, if the gold deposition parameters are carefully controlled. This observation is an important result as heating (or annealing) of the deposited gold can have a detrimental effect on the mechanical properties of the silicon on which the gold is deposited used in microsensors. The paper presents the investigation of the morphology and crystalline structure of Au film prepared by thermal evaporation at room temperature on silicon. The effect of gold deposition rate is studied, and it is shown that by increasing the deposition rate from 0.02 nm s-1 to 0.14 nm s-1 the gold surface RMS roughness decreases, whereas the grain size of the deposited gold is seen to follow a step function decreasing suddenly between 0.06 and 0.10 nm s-1. The XRD intensity of the preferentially [111] orientated gold crystallites is also seen to increase as the deposition rate increases up to a deposition rate of 0.14 nm s-1. Formation and characterization of 1-dodecanethiol on these Au coated samples is also studied using contact angle. It is shown that by increasing the Au deposition rate the contact angle hysteresis (CAH) decreases until it plateaus, for a deposition rate greater than 0.14 nm s-1, where the CAH is smaller than 9 degrees which is an indication of homogeneous SAM formation, on a smooth surface

Switching specific biomolecular interactions on surfaces under complex biological conditions

Herein, electrically switchable mixed self-assembled monolayers based on oligopeptides have been developed and investigated for their suitability in achieving control over biomolecular interactions in the presence of complex biological conditions. Our model system, a biotinylated oligopeptide tethered to gold within a background of tri(ethylene glycol) undecanethiol, is ubiquitous in both switching specific protein interactions in highly fouling media while still offering the non-specific protein-resistance to the surface. Furthermore, the work demonstrated that the performance of the switching on the electro-switchable oligopeptide is sensitive to the characteristics of the media, and in particular, its protein concentration and buffer composition, and thus such aspects should be considered and addressed to assure maximum switching performance. This study lays the foundation for developing more realistic dynamic extracellular matrix models and is certainly applicable in a wide variety of biological and medical applications

Engineering the mechanical and physical properties of organic–inorganic composite microcapsules

AbstractDouble-shell composite microcapsule with a ripened CaCO3 nanoparticle outer shell and melamine formaldehyde (MF)/copolymer inner shell shows advantages in adjustable permeability and mechanical strength, comparing with single shell microcapsules. Here, we have systematically studied the effects of certain formulation parameters on the properties of the double-shell composite microcapsules, i.e. the MF cross-linking time and the concentration of the aqueous CaCl2 and Na2CO3 used for the ripening process of CaCO3 nanoparticles. The properties of the microcapsules such as average diameter, wall thickness, degree of wall formation formed by the ripened CaCO3 nanoparticles, nominal rupture stress and leakiness were characterized

Electrically-driven modulation of surface-grafted RGD peptides for manipulation of cell adhesion

Reported herein is a switchable surface that relies on electrically-induced conformational changes within surface-grafted arginine–glycine–aspartate (RGD) oligopeptides as the means of modulating cell adhesion

Combined Experimental and Computational Study of Polyaromatic Hydrocarbon Aggregation:Isolating the Effect of Attached Functional Groups

To establish, and isolate, the influence of different chemical functional groups on the aggregation of polyaromatic hydrocarbons, a series of triphenylene-based compounds were investigated using a combined experimental and computational approach. Containing alkoxy side chains of varying lengths or amide appendages, both with and without a terminating carboxylic acid, their aggregation structures, sizes, and kinetics in toluene were studied over several length scales, using a combination of dynamic light scattering and diffusion-ordered nuclear magnetic resonance spectroscopy, complemented with molecular dynamics simulations. There is a strong correlation between molecular architecture and aggregation mechanisms: the addition of polar functional groups and heteroatoms resulted in compounds that are more prone to aggregation and form large, micrometer-sized clusters, while the increased steric hindrance imposed by alkoxy side chains led to stable nanometer-sized aggregates. These conclusions underline the strong structure-function relationship of polyaromatic hydrocarbons, such as asphaltenes, examined here over multiple length scales in a single solvent. We also demonstrate the importance of using complementary techniques to study the aggregation process of polyaromatic hydrocarbons that could form aggregates of various sizes over different time scales