nanoquebec 2006-11-14 08:37
Step-By-Step Surface Assembly
[b]Atomic force microscope attaches reactive polymer chain to a surface, one reaction at a time[/b]T;S$bG.o:v
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[color=green]Duwez' surface assembly reaction[/color]
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Molecular manufacturing's ultimate goal of assembling molecular machines atom by atom may be a long way off, but a research team in Europe has come a step closer to assembling structures molecule by molecule. In an elegant meeting of chemistry and mechanics at the single-molecule level, Anne-Sophie Duwez, a materials scientist at Belgium's University of Liège, and colleagues use an atomic force microscope (AFM) to covalently attach individual molecules to a surface, making and breaking each bond individually (Nat. Nanotechnol., DOI: 10.1038/nnano.2006.92).
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"The ultimate physical limit in the design and fabrication of organic surfaces can be reached using this approach," according to Duwez.R5Y(Sg4~7ty6b
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To achieve their mechanosynthesis, Duwez' group grafts poly-N-succinimidyl acrylate onto a gold-coated AFM tip. They then carefully bring this modified AFM tip into contact with a silicon surface functionalized with primary amines. A nucleophilic amine attacks a reactive carbonyl on the polymer, forming an amide linkage that effectively glues the polymer to the surface. Retracting the AFM tip breaks the weakest bond in the system, the Au-C bond that binds the polymer to the tip, leaving the polymer stuck to the surface.
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The deposited polymer's remaining succinimide groups can then react with other nucleophilic compounds, Duwez says. They can, for example, "serve as anchoring groups for the one-step immobilization of biological molecules." Delivering and positioning individual biological compounds, she says, would enable the investigation of biological recognition processes.4zW(G'su6x
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For high-throughput and massive parallel-patterning applications, the technique can't compete with recent advances in dip-pen nanolithography (C&EN, Oct. 2, page 13), Duwez notes. "Targeted molecule delivery is a delicate experiment based on the interplay between mechanical forces and a chemical reaction at the single-molecule level," she says. "The main advantage of our approach over dip-pen nanolithography is the resolution. The exact number of delivered molecules can be controlled."
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Ultimately, Duwez would like to create versatile AFM tips that work like molecular grippers able to build a complex structure, molecule by molecule.S [&mv:q"_+x!n
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Chemical & Engineering News
zhongguo 2007-09-29 08:50
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