Nanoparticles to increase adhesive properties of biologically secreted materials for surface affixing.

Surface adhesion in nature has been the focus of intense study over the past few years. Nevertheless, research in this field has primarily concentrated on understanding the chemical aspects of adhesion. While scientists have been able to determine some of the molecular structures present in the adhesives secreted by surface climbing or surface affixing biological systems such as mussels and barnacles, the fundamental adhesion mechanisms used by these systems are still unknown. This research paper focuses on the nano-scale morphological similarities of adhesive materials secreted from marine mussels, barnacles and ivy. We discovered that marine mussels secrete large amounts of adhesive materials in the form of nanoparticles for surface adhesion. This is in keeping with our previous work, which indicated a similar phenomenon for ivy. Both studies concur with earlier research on marine barnacles, polychaetes and sea stars. Taken together, these results indicate that nanoparticles are used by natural, biological systems to increase surface adhesion. These nanoparticle surface adhesion mechanisms have important implications in terms of engineering surface adhesive materials and devices.

Nanoparticles secreted from ivy rootlets for surface climbing.

Using atomic force microscopy, we observed ivy secretes nanoparticles through adhering disks of the ivy aerial rootlets which allow the plant to affix to a surface. We analyzed the organic composition of the secretions using high-performance liquid chromatography/mass spectrometry and were able to determine the formula of 19 compounds. This study suggests that the nanoparticles play a direct and important role for ivy surface "climbing". Weak adhesion and hydrogen bonding seem to be the forces for the climbing mechanism. This ivy secretion mechanism may inspire new methods for synthesizing nanoparticles biologically or new approaches to adhesion mechanisms for engineering applications.

A nanoengineering approach for investigation and regulation of protein immobilization.

It is known that protein attachment to surfaces depends sensitively upon the local structure and environment of the binding sites at the nanometer scale. Using nanografting and reversal nanografting, both atomic force microscopy (AFM)-based lithography techniques, protein binding sites with well-defined local environments are designed and engineered with nanometer precision. Three proteins, goat antibiotin immunoglobulin G (IgG), lysozyme, and rabbit immunoglobulin G, are immobilized onto these engineered surfaces. Strong dependence on the dimension and spatial distribution of protein binding sites are revealed in antibody recognition, covalent attachment via primary amine residues and surface-bound aldehyde groups. This investigation indicates that AFM-based nanolithography enables the production of protein nanostructures, and more importantly, protein-surface interactions at a molecular level can be regulated by changing the binding domains and their local environment at nanometer scale.

Nanografting for surface physical chemistry.

This article reveals the enabling aspects of nanografting (an atomic force microscopy-based lithography technique) in surface physical chemistry. First, we characterize self-assembled monolayers and multilayers using nanografting to place unknown molecules into a matrix with known structure or vice versa. The availability of an internal standard in situ allows the unknown structures to be imaged and quantified. The same approaches are applied to reveal the orientation and packing of biomolecules (ligands, DNA, and proteins) upon immobilization on surfaces. Second, nanografting enables systematic investigations of size-dependent mechanics at the nanometer scale by producing a series of designed nanostructures and measuring their Young's modulus in situ. Third, one can investigate systematically the influence of ligand local structure on biorecognition and protein immobilization by precisely engineering ligand nanostructures. Finally, we also demonstrate the regulation of the surface reaction mechanism, kinetics, and products via nanografting.

High-efficiency stepwise contraction and adsorption nanolithography.

A new miniaturization protocol is demonstrated using stretching and relaxation of an elastomer substrate. A designed microstructure is formed on the stretched substrate and subsequently becomes miniaturized when the substrate relaxes. More importantly, the miniaturized structures can be transferred onto a new substrate for further miniaturization or can be utilized as stamps for nanolithography of designated materials. As an example of this approach, an elastic mold was first cast from a Si mold containing periodic line arrays of 1.5-microm line width. Upon relaxation, line width is reduced to 240 nm. The new elastomer may be used as stamps for micro- and nanofabrication of materials such as proteins. The polymer surface roughness or wrinkling behavior at nanoscale is found to follow classic stability model in solid mechanics. This observation provides means to design and control the surface roughness to meet specific requirements.

Hybridization with nanostructures of single-stranded DNA.

Nanostructures of single-stranded DNA (ssDNA) were produced within alkanethiol self-assembled monolayers using nanografting, an atomic force microscopy (AFM) based lithography technique. Next, variations of the fabrication parameters, such as the concentration of ssDNA or lines per frame, allowed for the regulation of the density of ssDNA molecules within the nanostructures. The label-free hybridization of nanostructures, monitored using high-resolution AFM imaging, has proven to be highly selective and sensitive; as few as 50 molecules can be detected. The efficiency of the hybridization reaction at the nanometer scale highly depends on the ssDNA packing density within the nanostructures. This investigation provides a fundamental step toward sensitive DNA detection and construction of complex DNA architectures on surfaces.

Application of luminescent Eu:Gd2O3 nanoparticles to the visualization of protein micropatterns.

Nanoparticle phosphors made of lanthanide oxides are a promising new class of tags in biochemistry because of their large Stokes shift, sharp emission spectra, long luminescence lifetime, and good photostability. We demonstrate the application of these nanoparticles to the visualization of protein micropatterns. Luminescent europium-doped gadolinium oxide (Eu:Gd2O3) nanoparticles are synthesized by spray pyrolysis. The size distribution is from 5 to 200 nm. The particles are characterized by means of laser-induced fluorescent spectroscopy and transmission electron microscopy (TEM). The main emission peak is at 612 nm. The nanoparticles are coated with avidin through physical adsorption. biotinylated bovine serum albumin (BSA-b) is patterned on a silicon wafer using a microcontact printing technique. The wafer is then incubated in a solution of avidin-coated nanoparticles. Fluorescent microscopic images reveal that the nanoparticles are organized onto designated area, as defined by the microcontact printing process. The luminescent nanoparticles do not suffer photobleaching during the observation, which demonstrates their suitability as luminescent labels for fluorescence microscopy studies. More detailed studies are preformed using atomic-force microscopy (AFM) at a single nanoparticle level. The specific and the nonspecific binding densities of the particles are qualitatively evaluated.