Colloidal assemblies on patterned silane layers

Abstract

The site-selective assembly of colloidal polymer particles onto laterally patterned silane layers was studied as a model system for the object assembly process at mesoscale dimensions. The structured silane monolayers on silicon oxide substrates were fabricated by a combination of liquid-and gas-phase deposition of different trialkoxysilanes with a photolithographic patterning technique. By using this method various types of surface functionalizations such as regions with amino functions next to areas of the bare silica surface or positively charged regions of a quaternary ammonium silane surrounded by a hydrophobic octadecylsilane film could be obtained. Furthermore, a triethoxysilane with a photoprotected amino group was synthesized, which allowed direct photopatterning after monolayer preparation, leading to free NH2 groups at the irradiated regions. The different silane monolayer patterns were used to study the surface assembly behavior of carboxylated methacrylate particles by optical and scanning electron microscopy. In dependence of the assembly conditions (different surface functionalizations, pH, and drying conditions), a selective preference of the particles for a specific surface type versus others was found. Site-specific colloid adsorption could be observed also on the photosensitive silane layers after local deprotection with light. From the photosensitive silane and positively charged ammonium silane, molecularly mixed monolayers were prepared, which allowed particle adsorption and photoactivation within the same monolayer as shown by fluorescence labeling.O ne of the major driving forces in modern technology is based on the desire for miniaturization, which leads to smaller and lighter devices and a higher number of functional units per volume element. This tendency is prevalent particularly in microelectronics, optics, and sensors. Fabrication methods for small parts and structuring techniques have been developed very far, entering now the regime of nanoscopic dimensions (1, 2). Integrating individual objects of such dimensions into more complex structures and devices, on the other hand, represents a key challenge. Especially for the interfacing of nanoscopic devices with the macroscopic world, a large number of hierarchical organization levels are required to be implemented and controlled to actually use such small devices. One strategy toward attaining this goal emerges from the application of self-organization and assembly concepts that are ubiquitously present in the biological world and used successfully in supramolecular chemistry. Based on these principles several methods for the assembly of objects into two-and three-dimensional structures have been demonstrated at length scales from several nanometers up to millimeters (3-11). Most of these methods rely on shape complementarity of the objects, the surface tension at the interface of an auxiliary liquid and the object surfaces, and specific molecular interactions between the individual objects.A refined strategy for the assembly of mesos...

Wavelength-Selective Caged Surfaces: How Many Functional Levels Are Possible?

“…4b,5 Microarrays of peptides, 4b,6 oligonucleotides, 7 and peptoids 8 have been reported. Other species such as metallic nanoparticles, 9 polymer colloids, 3h,10 fluorescent dyes, 10,11 or biotinylated proteins 4e,12 have also been patterned using caged surfaces. We have used a similar approach to photoregulate cell adhesion and to obtain micropatterns of cells on different substrates.…”

Surface Patterning with Colloidal Monolayers

“…applied patterned, charged silane monolayers [62] for the same purpose. The strong interaction that drives the assembly process unfortunately prevents a high order in the colloidal monolayer as the individual particles lack mobility to find their hexagonal environment.…”

“…All of the 26 Theory mentioned processes are able to produce defined patterns of monolayers as well by prestructuring of the substrate. [61][62][63] Figure 3.3.3. Electrostatic deposition process as demonstrated by Zhang et al [63] .…”

Fabrication of patterned surfaces by photolithographic exposure of DNA hairpins carrying a novel photolabile group

“…Hybrid top-down/bottom-up processes, which combine the precision of lithographic techniques and the parallelism of self-assembly have been actively pursued in order to create patterns on silicon surfaces functionalised with self-assembled monolayers (SAMs) [5][6][7]. However, the ability to organise biomolecules, such as DNA on surfaces, such as glass [8,9] and gold [10][11][12] is an area of increased interest.…”