Macroporous silicon templated from silicon nanocrystallite and functionalized SiH reactive group for grafting organic monolayer

Fabrication and adhesion of a bio-inspired microarray: capillarity-induced casting using porous silicon mold

Inspired by the setal microstructure found on the gecko's toe-pads, a highly dense array of high-aspect-ratio (HAR) artificial setae has been developed with a novel mold-casting technique using a porous silicon (PSi) template. To overcome the high fluid resistance in the HAR capillary pores, the PSi template surface is modified with a monolayer coating of dimethylsilane. The coating exhibits similar chemical composition and surface energy to the precursor of the poly(dimethylsiloxane) (PDMS) replica. The compatibility between the template and the replica addresses the major challenge of molding HAR microstructures, resulting in high-resolution replicas of artificial PDMS microsetae with complicated geometry resembling a real gecko's setae. The artificial setae are characterized by a mean radius of 1.3 μm, an aspect ratio of 35.1, and a density of ~4.7 × 105 per mm2. Results from adhesion characterizations reveal that with increasing preload, the shear adhesion of micro-setae continually increases while the normal adhesion decreases. The unique adhesion performance is caused by both van der Waals forces and the elastic resistance of PDMS setae. With further structural optimizations and the addition of an actuation mechanism, artificial setal arrays might eventually demonstrate the fascinating adhesion performances of the gecko for mimetic devices such as wall-climbing devices.

GaN nanowire functionalized with atomic layer deposition techniques for enhanced immobilization of biomolecules

We report the use of atomic layer deposition (ALD) coating as a nanobiosensor functionalization strategy for enhanced surface immobilization that may enable higher detection sensitivity. Three kinds of ALD coating films, Al(2)O(3), TiO(2), and SiO(2), were grown on the gallium nitride nanowire (GaN NW) surfaces and characterized with high-resolution transmission electron microscopy (HRTEM) and vacuum Fourier transform infrared spectroscopy (FTIR). Results from HRTEM showed that the thicknesses of ALD-Al(2)O(3), ALD-TiO(2) and ALD-SiO(2) coatings were 4-5 nm, 5-6 nm, and 12-14 nm, respectively. Results from FTIR showed that the OH contents of these coatings were, respectively, ∼6.9, ∼7.4, and ∼9.3 times that of piranha-treated GaN NW. Furthermore, to compare protein attachments on the different surfaces, poly(ethylene glycol) (PEG)-biotin was grafted on the OH-functionalized GaN NW surfaces through active Si-Cl functional groups. Streptavidin protein molecules were then attached to the biotin ends via specific binding. The immobilized streptavidin molecules were examined with scanning electron microscopy, HRTEM, and fluorescent imaging. Results from HRTEM and energy-dispersive X-ray revealed that the nitrogen concentrations on the three ALD coatings were significantly higher than that on the piranha-treated surface. Results from fluorescent imaging further showed that the protein attachments on the Al(2)O(3), TiO(2), and SiO(2) ALD coatings were, respectively, 6.4, 7.8, and 9.8 times that of piranha-treated surface. This study demonstrates that ALD coating can be used as a functionalization strategy for nanobiosensors because it is capable of creating functional groups with much higher density compared to widely used acid modifications, and among the three ALD coatings, ALD-SiO(2) yielded the most promising results in OH content and protein attachment.