Arbitrary and Parallel Nanofabrication of 3D Metal Structures with Polymer Brush Resists

3D polymer brushes are reported for the first time as ideal resists for the alignment-free nanofabrication of complex 3D metal structures with sub-100 nm lateral resolution and sub-10 nm vertical resolution. Since 3D polymer brushes can be serially fabricated in parallel, this method is effective to generate arbitrary 3D metal structures over a large area at a high throughput.

Shape-controlled fabrication of micron-scale surface chemical gradients via electrochemically activated copper(i) "click" chemistry

We report an electrochemical method for the shape-controlled fabrication of micron-scale surface-bound chemical gradients. The approach is based on employing platinum microelectrode arrays on glass for the establishment of a Cu(i) solution gradient via local electrochemical reduction of Cu(ii) (cathodic reaction), and oxidation of the generated Cu(i) back to Cu(ii) (anodic reaction), under ambient conditions. The Cu(i) solution gradient, in the presence of an alkyne in solution and an azide monolayer on the glass surface in between the platinum electrodes, is exploited for the surface-confined gradient fabrication via the Huisgen 1,3-dipolar cycloaddition (CuAAC). Owing to the high sensitivity of the CuAAC on the Cu(i) concentration, we demonstrate here the control of the shape of the micron-scale surface gradient, in terms of steepness and surface density, as a function of the reaction conditions. The surface gradients were assessed by fluorescence microscopy and time-of-flight secondary ion mass spectrometry (Tof-SIMS). Moreover, bi-component and biomolecular gradients have been fabricated and a method for the electrochemically mediated patterning of surface chemical gradients on external azide-functionalized substrates has been developed for the implementation of bi-directional 2D surface gradients.

Preparation of amphiphilic polymer-functionalized carbon nanotubes for low-protein-adsorption surfaces and protein-resistant membranes

Multiwalled carbon nanotubes functionalized with poly(sulfone) (PSF) and poly(sulfobetaine methacrylate) (PSBMA) (MWNT-PSF/PSBMA) have been prepared through sequential atom transfer radical polymerization. The structure of MWNT-PSF/PSBMA hybrid has been characterized with FTIR, Raman spectroscopy, and high-resolution transmission electron microscopy. Incorporation of PSBMA chains to MWNTs introduces amphiphilic and protein-resistant properties to MWNT-PSF/PSBMA. Addition of 1 wt % MWNT-PSF/PSBMA to PSF films significantly improves their protein-resistant characteristic, as the composite films show a 4.4% of protein adsorption compared to poly(styrene) Petri dishes. The PSF/MWNT-PSF/PSBMA composite has been applied to prepare antifouling ultrafiltration membranes for protein separation. This work demonstrates an effective and convenient approach to prepare low-protein-adsorption surfaces and antifouling membranes.

Adjustment of the bioresistivity by electron irradiation: self-assembled monolayers of oligo(ethyleneglycol)-terminated alkanethiols with embedded cleavable group

The bioresistivity of protein-repelling films, such as e.g. oligoethyleneglycol (OEG) bearing self-assembled monolayers (SAMs), can be adjusted by electron irradiation. We have studied the effect of an embedded irradiation-sensitive functional group (so called "weak link") on the irradiation sensitivity of such films. As test systems, we used two OEG-substituted alkanethiolate SAMs with different lengths of the OEG chain and a sulfone group serving as a "weak link" moiety; this group was embedded between the OEG and alkyl chains of the target molecules. The expected cleavage of the molecular chains at the predetermined "weak link" position was found to be accompanied by direct damage of the OEG matrix, with a dominance of the latter process in the case of a long OEG chain. At the same time, in the case of short OEG chain, the insertion of sulfone group resulted in a noticeable gain in the irradiation sensitivity of the respective SAMs and, consequently, in enhanced tunability of their protein-adhesive properties. These films, along with other OEG-substituted SAMs and polymer layers with and without an embedded weak link moiety, can be used as primary matrices for the fabrication of different protein patterns by electron beam lithography.

Fabrication of mixed self-assembled monolayers designed for avidin immobilization by irradiation promoted exchange reaction

An applicability of irradiation-promoted exchange reaction (IPER) to the fabrication of mixed self-assembled monolayers (SAMs) composed of the protein-repelling matrix and the moieties bearing binding sites for specific attachment of a target protein is demonstrated. As test systems, we took mixed films of oligoethylene glycol (OEG)-substituted alkanethiols (OEG-ATs) and biotin-substituted alkanethiols (BATs) on Au{111}. Such SAMs are suitable for the specific immobilization of avidin protein and its variants. The composition of the mixed OEG-AT/BAT SAMs could be precisely controlled by varying the irradiation dose, which is important prerequisite for the fabrication of the respective patterns by electron-beam lithography. While the general trend in the immobilization of avidin onto the mixed OEG-AT/BAT SAMs prepared by IPER was found to be consistent with the earlier reports regarding the analogous films fabricated by the coassembly method, the concentration of the BAT component in the mixed SAMs needed for the maximum surface coverage of the specific protein was found to be somewhat lower, and the maximum avidin coverage somewhat higher in the case of IPER as compared to the coassembly method. We ascribe these differences to the lack of phase segregation and better separation of the individual BAT species in the OEG-AT matrix in the case of IPER.