The Ethical and Social Dimensions of Chemistry: Reflections, Considerations, and Clarifications.

"Ethics in Chemistry" is a huge topic with various viewpoints and arguments on what it actually is and what compliance to ethical guidelines and participation in ethical discourse imply, covering principles of science and research ethics, profession ethics, and technology ethics. Overview and clarity are lost easily. The authors-members of the recently formed EuCheMS working party "Ethics in Chemistry"-present an attempt to collect and sort the ethically relevant aspects and challenges that chemists see themselves confronted with. Based on this list, strategies for ethical action are outlined. On the one hand, there are those issues that are a matter of compliance to existing guidelines and standards. On the other hand, there are those conflicts that arise at the intersection of science, technology and society and that need engaged chemists participating in the larger discourse for sustainability. This Editorial attempts to point out why this is important and what chemists can do in particular.

Fabrication of a carbon-nanotube-based field-effect transistor by microcontact printing.

The fabrication of a field-effect transistor with both channel material and source and drain electrodes made from carbon nanotubes (CNTs) through patterned deposition of CNT films by microcontact printing is described. Surfactant-dispersed single-walled CNTs are first separated into semiconducting and metallic fractions by gel filtration. The semiconducting and metallic CNTs are then sequentially transferred by dendrimer-coated polydimethylsiloxane stamps onto dendrimer-coated silicon wafers following a printing protocol optimized for this purpose. The resulting CNT micropatterns are visualized by atomic force microscopy. Semiconducting as well as metallic CNTs preserve their characteristic electronic properties within the transferred films. A device composed of a rather thick (ca. 5 nm) and densely patterned film of metallic CNTs cross-printed on top of a thinner (ca. 1.5 nm) and less dense film of semiconducting CNTs shows the typical properties of a field-effect transistor with the metallic CNT stripes as electrodes, the semiconductive CNT stripes as channel material, and the silicon substrate as gate electrode.

Click chemistry by microcontact printing on self-assembled monolayers: a structure-reactivity study by fluorescence microscopy.

Microcontact printing (µCP) has developed into a powerful tool to functionalize surfaces with patterned molecular monolayers. µCP can also be used to induce a chemical reaction between a molecular ink and a self-assembled monolayer (SAM) in the nanoscale confinement between stamp and substrate. In this paper, we investigate the Huisgen 1,3-dipolar cycloaddition, the Diels-Alder cycloaddition and the thiol-ene/yne reaction induced by µCP. A range of fluorescent alkyne inks were printed on azide SAMs and fluorescence microscopy was used to monitor the extent of the 1,3-dipolar cycloaddition on a glass substrate. The rate of cycloaddition depends on the reactivity of the alkyne and on the presence of Cu(I). The cycloaddition is accelerated by Cu(I) but it also proceeds readily in the absence of Cu(I). In addition, a range of fluorescent diene inks were printed on alkene SAMs on glass. In this case, fluorescence microscopy was used to monitor the rate of the Diels-Alder cycloaddition as well as its retro-reaction. Finally, fluorescent thiol inks were printed on alkene SAMs on glass, and fluorescent alkenes and alkynes were printed on thiol SAMs. It is shown that reactions by µCP follow structure-reactivity relationships similar to solution reactions. Under optimized conditions all reactions lead to dense microarrays of addition products within minutes of printing time.

Bacterial motility and clustering guided by microcontact printing.

Type IV pili are bacterial nanomotors that mediate two opposing behaviors on surfaces, spreading and clustering. Here we show that the velocity of motile Neisseria gonorrhoeae depends quantitatively on the fluidity of the phospholipid membrane surface. Using microcontact printing, we confined the surface motility to nonfluid islands within a fluid lipid membrane. On an array of islands, the transition from spreading to clustering was analyzed in real time and at the single cell level, showing that it was triggered by the number of bacteria (7.5 +/- 0.3) for small islands and by the surface density (56 +/- 2%) when the size of the island exceeded 25 microm(2).