A new
cysteine-based methacrylic monomer (CysMA) was conveniently
synthesized via selective thia-Michael addition of a commercially
available methacrylate-acrylate precursor in aqueous solution without
recourse to protecting group chemistry. Poly(cysteine methacrylate)
(PCysMA) brushes were grown from the surface of silicon wafers by
atom-transfer radical polymerization. Brush thicknesses of ca. 27
nm were achieved within 270 min at 20 °C. Each CysMA residue
comprises a primary amine and a carboxylic acid. Surface zeta potential
and atomic force microscopy (AFM) studies of the pH-responsive PCysMA
brushes confirm that they are highly extended either below pH 2 or
above pH 9.5, since they possess either cationic or anionic character,
respectively. At intermediate pH, PCysMA brushes are zwitterionic.
At physiological pH, they exhibit excellent resistance to biofouling
and negligible cytotoxicity. PCysMA brushes undergo photodegradation:
AFM topographical imaging indicates significant mass loss from the
brush layer, while XPS studies confirm that exposure to UV radiation
produces surface aldehyde sites that can be subsequently derivatized
with amines. UV exposure using a photomask yielded sharp, well-defined
micropatterned PCysMA brushes functionalized with aldehyde groups
that enable conjugation to green fluorescent protein (GFP). Nanopatterned
PCysMA brushes were obtained using interference lithography, and confocal
microscopy again confirmed the selective conjugation of GFP. Finally,
PCysMA undergoes complex base-catalyzed degradation in alkaline solution,
leading to the elimination of several small molecules. However, good
long-term chemical stability was observed when PCysMA brushes were
immersed in aqueous solution at physiological pH.
The silver-nucleoside complex [Ag(i)-(N3-cytidine)2]+, 1, self-assembles to form a supramolecular metal-mediated base-pair array highly analogous to those seen in metallo-DNA.
Advances in bottom-up material design have been significantly progressed through DNA-based approaches. However, the routine integration of semiconducting properties, particularly long-range electrical conduction, into the basic topological motif of DNA remains challenging. Here, we demonstrate this with a coordination polymer derived from 6-thioguanosine (6-TG-H), a sulfur-containing analog of a natural nucleoside. The complexation reaction with Au(I) ions spontaneously assembles luminescent one-dimensional helical chains, characterized as {AuI(μ-6-TG)}n, extending many μm in length that are structurally analogous to natural DNA. Uniquely, for such a material, this gold-thiolate can be transformed into a wire-like conducting form by oxidative doping. We also show that this self-assembly reaction is compatible with a 6-TG-modified DNA duplex and provides a straightforward method by which to integrate semiconducting sequences, site-specifically, into the framework of DNA materials, transforming their properties in a fundamental and technologically useful manner.
Zwitterionic materials display antifouling promise, but their potential in marine anti-biofouling is still largely unexplored. This study evaluates the effectiveness of incorporating small quantities (0-20% on a molar basis) of zwitterions as sulfobetaine methacrylate (SBMA) or carboxybetaine methacrylate (CBMA) into lauryl methacrylate-based coatings whose relatively hydrophobic nature encourages adhesion of the diatom Navicula incerta, a common microfouling organism responsible for the formation of 'slime'. This approach allows potential enhancements in antifouling afforded by zwitterion incorporation to be easily quantified. The results suggest that the incorporation of CBMA does provide a relatively minor enhancement in fouling-release performance, in contrast to SBMA which does not display any enhancement. Studies with coatings incorporating mixtures of varying ratios of the cationic monomer [2-(methacryloyloxy)ethyl]trimethylammonium chloride and the anionic monomer (3-sulfopropyl)methacrylate, which offer a potentially lower cost approach to the incorporation of anionic and cationic charge, suggest these monomers impart little significant effect on biofouling.
The photocatalytic self-cleaning characteristics of titania facilitate the fabrication of re-useable templates for protein nanopatterning. Titania nanostructures were fabricated over square centimeter areas by interferometric lithography (IL) and nanoimprint lithography (NIL). Using a Lloyd's mirror two-beam interferometer, self-assembled monolayers of alkylphosphonates adsorbed on the native oxide of a Ti film were patterned by photocatalytic nanolithography. In regions exposed to a maximum in the interferogram, the monolayer was removed by photocatalytic oxidation. In regions exposed to an intensity minimum, the monolayer remained intact. After
We
show that sequential protein deposition is possible by photodeprotection
of films formed from a tetraethylene-glycol functionalized nitrophenylethoxycarbonyl-protected
aminopropyltriethoxysilane (NPEOC-APTES). Exposure to near-UV irradiation
removes the protein-resistant protecting group, and allows protein
adsorption onto the resulting aminated surface. The protein resistance
was tested using proteins with fluorescent labels and microspectroscopy
of two-component structures formed by micro- and nanopatterning and
deposition of yellow and green fluorescent proteins (YFP/GFP). Nonspecific
adsorption onto regions where the protecting group remained intact
was negligible. Multiple component patterns were also formed by near-field
methods. Because reading and writing can be decoupled in a near-field
microscope, it is possible to carry out sequential patterning steps
at a single location involving different proteins. Up to four different
proteins were formed into geometric patterns using near-field lithography.
Interferometric lithography facilitates the organization of proteins
over square cm areas. Two-component patterns consisting of 150 nm
streptavidin dots formed within an orthogonal grid of bars of GFP
at a period of ca. 500 nm could just be resolved by fluorescence microscopy.
We demonstrate that interferometric lithography offers a fast, simple route to nanostructured self-assembled monolayers of alkylphosphonates on the native oxide of titanium. Exposure at 244 nm using a Lloyd's mirror interferometer caused the spatially periodic photocatalytic degradation of the adsorbates, yielding nanopatterns that extended over square centimetre areas. Exposed regions were re-functionalised by a second, contrasting alkylphosphonate, and the resulting patterns were used as templates for the assembly of molecular nanostructures; we demonstrate the fabrication of lines of polymer nanoparticles 46 nm wide. Nanopatterned monolayers were also employed as resists for etching of the metal film. Wires were formed with widths that could be varied between 46 and 126 nm simply by changing the exposure time. Square arrays of Ti dots as small as 35 nm (λ/7) were fabricated using two orthogonal exposures followed by wet etching.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.