Functional Spacers Research Articles

Formation of photoresponsive gold nanoparticle networks via click chemistry

To tailor highly-functionalized gold nanoparticle (GNP) networks, we investigated the GNP network formation with functionalized spacer group via click chemistry. This is based on its high reactivity and mild reaction conditions. The feature of this protocol is the easy approach to versatile GNP functionalization on the basis of the excellent accessibility and good stability of functional dialkyne derivatives. We achieved the successful formation of GNP networks by reacting azide-appended GNPs and various dialkyne derivatives, supported by infrared absorption spectroscopy and transmission electron microscopy analyses. These GNP networks readily showed the unique physical properties similar to those of classical GNP networks prepared by ligand exchange reaction of bidentate functional spacers. Typically, the GNP network with the azobenzene unit as a functional spacer (GNP3) showed reversible photoinduced formation of three-dimensional aggregates followed by its isomerization in the network.

Selective Attachment of Mammalian Cells and Polystyrene Microbeads to Functional Amine Patterns Defined by Perfluoroalkyl Silane Surfaces

Surface modification technologies have been widely utilized for the investigation of the effect of surface properties on selective attachment of cells and cell functions. Recently, hydrophobic surfaces modified with organosilanes such as dichlorodimethyl silane and perfluoroalkyl silane have been shown to form a resistant barrier for cell attachment owing to their low surface energy. Moreover, they provide a chemically inert background and prevent the cross-contamination of liquid droplets on different spots. These characteristics have the potential to be utilized in the application of spot synthesis and array-type cell-based assays. To date, there have been a few reports on the formation of amine patterns defined by hydrophobic silane layers for the spatial organization of cells. However, several problems, such as the use of the limited types of organosilane for the cell-adhesive patterns, complicated deep UV irradiation for the patterning, and possible contamination of patterns from organosilane coupling still remain to be overcome. Therefore, it is necessary to develop a new patterning technique that extends the versatile surface chemistry and eliminates the contamination problem. Here, we present a novel and simple surface modification method for preparing amine-spacer patterns defined by perfluoroalkyl silane layers and their feasibility for the directed attachment of human retinal pigment epithelial cell line (ARPE-19) and functional polystyrene microbeads. In particular, we have devoted special efforts to solving the contamination problem, which is generated from the conventional photolithography and organosilane coupling method. As illustrated in Figure 1, our strategy is based on the two-step silanization with a simple photoresist (PR) process and then subsequent diamine coupling. To simplify the PR lift-off process, we have designed a home-made rubber stamp for PR printing directly on the substrate in a short time without any further treatment. Formation of isocyanate layers using isocyanatopropyl triethoxysilane (IPTS) on the substrates makes it possible to introduce a variety of amino functional spacers on the surface via urea linkages. In this study, we employed hydrophilic diamine spacers such as 4,7,10-trioxa-1,13-tridecanediamine (TEGdiamine) and Jeffamine ED-600 (PEGdiamine) for the creation of amino-terminal groups that can serve as charged domains promoting cell adhesion, as well as the starting point for the versatile surface modification. Here, we investigated two methods for preparing the fundamental amine-spacer patterns defined by the perfluoroalkyl silane. As illustrated in Figure 1 (Method 1), the PR was patterned on the acid-treated glass substrate by stamping. Thereafter, perfluoroalkyl silane layers (1H,1H,2H,2H-perfluorodecylmethyldichlorosilane, 17F) were formed on the exposed glass surface of the patterned substrates. Subsequently, after the removal of the PR on the substrates with acetone, the substrates were reacted with IPTS to produce patterned reactive sites. However, we found that the 17F layers were contaminated by IPTS coupling and the following amination process, so that substrates were no longer resistant to cell adhesion. In general, functional silane compounds having

Alkanethiolate Self-Assembled Monolayers as Functional Spacers to Resist Protein Adsorption upon Au-Coated Nerve Microelectrode

Alkanethiolate self-assembled monolayers (SAMs) of varied chain lengths were adsorbed upon Au-coated nerve microelectrodes and employed as protein-resistant spacers. The microelectrode spiraled as a cuff type can be used for restoring motor function via electrical stimulation on the peripheral nerve system; however, an increase of electrode impedance might occur during implantation. In this work, a thin-film SAMs treatment upon Au/polyimide (PI) surface of the microelectrode provided a hydrophobic characteristic, which retarded protein adsorption at the initial stage and subsequent pileup (or thickening) process. The protein-resistant effect exhibited comparable SAMs of different chain lengths adsorbed upon Au/PI surfaces. The increase of electrode impedance as a function of protein deposition time was mainly correlated with the addition of reactance that was associated with the pileup thickness of the deposited protein. Particularly, the SAMs-modified surface was capable to detach a significant portion of the accumulated protein from the protein-deposited SAMs/Au/PI, whereas the protein-deposited layers exhibited firm adhesion upon Au/PI surface. It is therefore very promising to apply thin-film SAMs adsorbed upon Au-coated surface for bioinvasive devices that have the need of functional electrical stimulations or sensing nerve signals during chronic implantation.

Poly(triacetylene)s: A New Class of Linearly π-Conjugated Oligomers and Polymers with an All-carbon Backbone

Linearly π-conjugated polymers are intensively investigated in both academia and industry for a diversity of advanced materials applications. Polyacetylenes (PAs) and poly(diacetylene)s (PDAs) were among the earliest investigated linearly π-conjugated polymers possessing an all-carbon backbone. They actually represent the first members in an entire progression of linear all-carbon polymers which starts with polyacetylene and ultimately extends to carbyne. Here, we describe the discovery and systematic investigation of poly(triacetylene)s (PTAs), the third class of compounds in this progression. We report both the preparation of longer-chain polydisperse PTA polymers as well as the synthesis, characterization, and physical study of monodisperse oligomers with record lengths extending up to 18 nm. We show how molecular properties evolve into the saturation range with increasing oligomeric length and report several direct determinations of the effective conjugation length (ECL), i.e. the oligomeric length at which saturation of molecular properties occurs. Finally, we present a new class of hybrid oligomers and polymers, with a diversity of chromophores inserted as functional spacers into the PTA backbone for further enhancement of optoelectronic properties.